- Ei，ESCI收录期刊
- 中国科学引文数据库(CSCD)核心期刊
- 中文核心期刊
- 文摘与引文数据库(Scopus)
- 剑桥科学文摘(CSA)
Supercapacitors are a new type of energy storage element that has been rapidly developed in recent years. The most important factor that determines the performance of supercapacitors is electrode materials. The development of low-cost, high-performance electrode materials is an important research direction for current supercapacitors. Metal-organic frameworks (MOFs) are a class of porous materials. The applications of MOFs in the supercapacitor have attracted more and more researchers due to their diverse composition and structure, large specific surface area, controllable structure and adjustable pore size. Recent researching application progress of pristine MOFs, MOFs-derived(porous carbon, metal oxides, porous carbon/metal oxides) and MOFs-composite materials for supercapacitors was summarized in this paper. The MOFs with different structural characteristics and their specific performance in the field of electrochemical energy storage were discussed. MOFs based supercapacitors are demonstrated to play an important role in the field of new energy storage and conversion. Finally, the current challenges, future trends and prospects of MOFs in the field of ultracapacitors were pointed out.
High voltage Li- and Mn-rich layered oxide (LMRO) electrodes with different amount of conductive carbon black Super P were investigated to explore the effect of carbon black on electrochemical performance of the electrode and scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) were utilized to study the internal reason why the amount of Super P affects the performance of the electrode. The results show that the performance of cycle stability and high-rate capability of LMRO electrodes exhibit the tendency of increasing first and then decreasing with increase of Super P content, while the optimum performance of electrodes is obtained at 5% (mass fraction, the same below). With the increase of Super P content, electronic contact between LMRO particles and Super P particles can be improved, electrically conductive network can be constructed, resistance between electrode components can be decreased, and electrode polarization can be reduced. However, when the content is higher than 5%, Super P particles are easily agglomerated, which is undesirable for further improving the conductivity of electrode.
Multiwalled carbon nanotubes(MWCNTs) were fluorinated to get the material of MWCNTs fluoride with different atomic ratio. The ratio of fluorine and carbon was 0.28(CF0.28), 0.56(CF0.56) and 0.78(CF0.78) respectively. The fluoride MWCNTs were used as cathode active material to coat on aluminum foil, lithium metal foil as counter electrode in Li/CFx batteries. The structures and properties were characterized by thermal gravimetric analyzer(TGA), scanning electron microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD), and X-ray photoelectron spectroscopy(XPS). The electrochemical performance was tested by galvanostatic discharge test. The results show that the battery with CF0.78 has the best electrochemical performance. At the current density of 39mA/g, the battery displays high discharge specific capacity of 724mAh/g and appears with a more stable platform for the discharge process. At the current discharge rate of 0.05C, the utilization of three kinds of MWCNTs fluoride electrodes is 73.4%, 89.6%, 92.9%. When the discharge rate is 2C, batteries with three different MWCNTs fluoride have discharge specific capacity attenuation rate of 68.8%, 34.1%, and 39.6%. It indicates that the discharge specific capacity attenuation rate can be mitigated to a certain extent with the improved level of fluoridation. Although the discharge capacity attenuation rate of CF0.78 is higher than that of CF0.56, CF0.78 has the most stable discharge curve at the same discharge rate.
Na0.5Bi0.48Sr0.02Ti0.98Mg0.02O2.97 compound was synthesized by solid-state reaction. AC impedance and internal friction spectroscopy were employed to study the electrical performance and oxgyen ion diffusion in the Sr, Mg-co-doped Na0.5Bi0.5TiO3 compounds. The grain conductivity of Na0.5Bi0.48Sr0.02Ti0.98Mg0.02O2.97 sample can reach 5.31×10-4 S/cm at 593 K, an order of magnitude higher than that of the Na0.5Bi0.5TiO3 compound at the same temperature and exceeding the grain conductivity of Na0.5Bi0.5Ti0.98Mg0.02O2.98 sample at 673K. An internal friction relaxation peak was observed. The relaxation parameters can be calculated, E=0.85eV and τ0=7.4×10-14s. Judging from the relaxation parameters and structural analysis, the Sr2+ dopant can amplify the specific free volume. Compared with the Na0.5Bi0.5Ti0.98Mg0.02O2.98 sample, the substantial increase of the grain conductivity for Na0.5Bi0.48Sr0.02Ti0.98Mg0.02O2.97 sample may be derived from the larger specific free volume, higher mobile oxygen vacancy content and better oxygen vacancy mobility.
Nano-infiltration and transient eutectic (NITE) process is a new method for fabricating silicon carbide fiber reinforced silicon carbide based (SiCf/SiC) composites, which has the advantages of short production cycle, simple process and low production cost. The material made by NITE process is with compact matrix, low porosity, and free of residual silicon, therefore, it is suitable for high temperature and long service environments at 1400℃ and above. At present, Japan, the United States and other countries have carried out in-depth research on this technology based on the mature third-generation silicon carbide fiber, and applied the composites in fields such as nuclear energy industrial heat exchangers and aero-engine combustor liners. In this paper, the basic concepts, the manufacturing process, the mechanical properties of SiCf/SiC composites and component verification and prospects of NITE process were reviewed, in order to provide the reference to a certain degree for the domestic development of this process.
The computational material science based on molecular dynamics method is critical for the investigation of the micro-nano scale plastic deformation, which helps to clarify the competition relationship between different plastic deformation mechanisms of magnesium alloys.The mechanism of slip, twinning and grain boundary sliding in magnesium alloys was summarized; the basic principles of molecular dynamics and the potential functions commonly applied to the hexagonal close-packed structure metals were briefly introduced. Moreover, the research progress of plastic deformation mechanism of Mg alloys based on the molecular dynamics was mainly analyzed. Based on the main problems mentioned above, it was pointed out that the development of high-precision potential function for magnesium alloy multiple systems and how to achieve the relationship of multiple scales will be the focused directions in the further research.
Mechanical metamaterial composed of chiral honeycomb structure is high performance engineering materials developed in recent years. They have the advantages of light weight, high specific stiffness, negative Poisson's ratio, adjustable structural parameters and stable mechanical properties. It not only can realize the dual mechanical functions of in-plane deformation and out-of-plane load-bearing, but also has excellent engineering application performance such as vibration isolation and sound absorption and noise reduction and control of elastic wave propagation. It has great potential in the fields of intelligent structure, vehicle, ship, aerospace and so on. Two mechanical aspects of its elastic properties and impact resistance were reviewed.First, the progress of theoretical analysis and research on the elastic properties such as the surface poplar modulus, negative Poisson's ratio, and elastic properties of external shear modulus of mechanical metamaterials were reviewed and commented. Further, in the aspect of impact resistance, the overall deformation and impact resistance of the existing chiral honeycomb mechanical metamaterials under impact load were reviewed based on perspectives of model establishment and finite element analysis. Finally, it was pointed out that in the further research of elasticity and impact properties, the mechanical model of internal ligament deformation and force transmission can be further established and the energy absorption mechanism of the impact process to be further explored so as to provide the reference for the optimization design of the internal structure of ligaments and node rings in this type of metamaterial.
based on the "octahedral structure model" of three-dimensional reticulated porous materials, the mathematical deductions are introduced one by one for the mathematical relations of their basic physical and mechanical properties in this paper. the present review on these deductions covers the unidirectional tension and the multidirectional tension/compression of porous materials, as well as the conductivity and the fatigue property. emphasis is placed on describing the equivalent circuit of the inner structure of porous materials, and the force action model both of quasi-rigid body and deformed body structure of porous materials under unidirectional tension. on this basis, the compressive strength is discussed, and the biaxial tension and triaxial tension/compression are mathematically deducted and analyzed. according to this octahedron model, the mathematical relations of mechanical properties can be also obtained from the deduction of unidirectional tension and compression, for porous materials under loading of non-direct tension and compression.
A series of copolymers (P(AA-co-MPC)) with acrylic acid (AA) and 2-methacryloy-loxyethyl phosphorylcholine (MPC) monomers were synthesized via RAFT polymerization. Then the magnetic iron oxide nanoparticles were modified by these synthesized copolymers through chemical coprecipitation method. Copolymers and the nanoparticles were characterized by 1H NMR, FTIR, GPC, TG, TEM, XRD, Zeta potential and particle size analyser, and Squid-VSM magnetic measure system. The results show that the P(AA-co-MPC) with narrow molecular mass distribution is successfully synthesized by RAFT polymerization and the surface of the magnetic iron oxide nanoparticles is modified by these copolymers. The modified magnetic iron oxide nanoparticles by copolymer synthesized with the monomer molar ratio of AA:MPC of 1:1 exhibit the best dispersion, the smallest hydrodynamic particle size (36.54±4.00) nm, the narrowest particle size distribution and the highest Zeta potential (-30.98±1.25) mV. The saturation magnetization is 65.57A·m2·kg-1. The nanoparticles show superparamagnetism, with no residual magnetism and zero coercive force.
CdSe/TiO2 heterojunction thin films were prepared by electrodeposition of CdSe nanoparticles on TiO2 nanotube arrays(TNTs). The effect of annealing temperature of TNTs (200, 350, 450, 600℃) on photoelectrochemical properties of CdSe/TiO2 heterojunctions thin films was discussed. The microstructure, crystal structure and photoelectric chemical properties of the samples were characterized by SEM, XRD, UV-Vis, electrochemical test and other methods. The results show that the cubic CdSe nanoparticles are uniformly deposited on the nozzles and walls of TNTs. When TNTs is amorphous without annealing or with annealing at 200℃, CdSe nanoparticles deposited on TNTs appear with less quantity and smaller size. The photoelectrochemical properties of CdSe/TiO2 heterojunctions thin films is very poor, and photocurrent density value almost reaches zero. As the annealing temperature increasing to 350℃, anatase phase is observed in TNTs. Consequently, CdSe nanoparticles show more quantity and lager size. Furthermore, the photoelectrochemical performance improves. The photocurrent density reaches the maximum value 4.05mA/cm2 at the annealing temperature of 450℃. However, when the annealing temperature continually increases to 600℃, rutile phase is formed in TNTs, CdSe nanoparticles become small and few and the photoelectrochemical performance decreases.
Titanium dioxide/graphene (TiO2/G) composite conductive materials were prepared by modified hydrothermal method. The effects of hydrothermal temperature and the amount of graphene on the electrical conductivity of the composites were investigated. The structure, microstructure and conductivity of the composites were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and so on, and the optimum hydrothermal temperature and the optimum doping amount of graphene were determined. The results show that the electrical conductivity of TiO2/G is the best when the content of graphene is 5% (mass fraction), the hydrothermal temperature is 160℃, and its resistivity is 13.46Ω·cm. The nano TiO2 in the composite is a spherical anatase phase with a diameter of about 100-200nm, and it is grown uniformly on the lamellar surface of graphene. Among them, the nano TiO2 is grown on the graphene layers, which effectively prevents the agglomeration of the graphene layer, which is beneficial to the formation of conductive network between the graphene layers, improves the efficiency of electron migration, and endows the titanium dioxide composites with excellent electrical conductivity.
KH-SiO2 was obtained by using 3-glycid-oxypropyl-trimethoxy-silane (KH-560) to modify nano-silica (nano-SiO2). KH-SiO2/PES/BMI-F51 multi-phase composite was prepared, the phenolic epoxy resin (F51) and bismaleimide (BMI) as the matrix, 4%(mass fraction, the same below) polyethe-rsulfone (PES) as toughening agent and different contents (0.5%-2.5%) of KH-SiO2 as modifier. The results of Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM) and transmission electron microscope (TEM) show that the surface modification of nano-SiO2 is favourable, the agglomeration tendency of nanoparticles is weakened, the size is decreased and the specific surface area is increased. Dielectric properties test displays that the dielectric constant of the material is decreased first and then increased with the increase of doping amount of KH-SiO2. There is no significant change in dielectric loss tangent, and the volume resistivity and breakdown strength are increased first and then decreased. The dielectric constant and dielectric loss tangent of composite reach 4.55 and 0.0029 at 10Hz, respectively, when the doping amount of KH-SiO2 is 1.5%. The volume resistivity and breakdown strength are 1.74×1014Ω·m and 29.11kV/mm, respectively, which are 68.9% and 35.9% higher than that of resin matrix.
The carbon fiber/epoxy resin composites were prepared by the resin transfer molding (RTM) process. Effect of resin toughness and carbon fiber type on the high speed impact properties was investigated using the air cannon impact test. The effect of high speed impact damage on the residual compressive property of the composites was studied by the compression performance test of the samples which were impacted at high speed. The results demonstrate that the resin toughness can greatly reduce the internal damage degree of composite materials subjected to high speed impact, and can improve the anti-high speed impact property and residual compressive property of the composites. Also, the anti-high speed impact property of T700S carbon fiber reinforced composites is superior to that of the T800H carbon fiber reinforced composites. The results also indicate that failure modes are highly dependent on the impact velocity. Specifically, when the impact velocity is low, the composites appear a circular pit on the impact surface while the back surface appears a convex protrusion. Also, when the impact velocity is high, a circular hole is formed on the impact surface of composites, and the tearing fracture along the fiber direction is observed on the back surface.
The surface conditions of the two different T800 carbon fibers by the wetting (T800HB) and the dry jet-wetting spinning processes (T800SC) were characterized and analyzed by scanning electron microscope (SEM), atomic force microscope (AFM), X-ray photoelectron spectroscope (XPS) and contacting-angle measuring instrument. The mechanical properties of their multifilaments, NOL rings and unidirectional laminates were evaluated by universal material testing machine. Results show that the surface of T800HB by wetting process is rougher, while the surface of T800SC by dry jet-wetting process is more chemical-active. Both chemical interaction and mechanical engagement between fiber and resin matrix result in the similar interlaminar shear strength (ILSS) of T800HB and T800SC. However, when the composite is damaged, the interfacial bonding of T800HB/resin seems tighter dominated by the mechanical engagement, leading to brittle fracture feature of T800HB reinforced composite, while T800SC reinforced composite exhibits ductile fracture feature with weaker interfacial bonding. In addition, the tensile strength of filament of T800SC is higher than that of T800HB. Accordingly, the tensile strength of NOL ring and unidirectional laminate composite of T800SC are higher than those of T800HB. Therefore, in combination of mechanical properties of carbon fibers by two kinds of spinning processes and their reinforced composites, as well as their fracture features, compared with T800HB, T800SC is more suitable to be the reinforcement of the composite fabricated by filament winding process.
In order to reduce the aircraft mass via high-temperature composite structures, and to extend the application of domestic T800 carbon fiber reinforced cyanate ester composites system, the sizing was analyzed, and the cyanate ester formulation was designed for the carbon fiber based on the sizing analysis. Meanwhile, the mechanical properties and heat resistance of the domestic T800 carbon fiber/cyanate ester composites were studied, and the effect of matrix on the composites interface was studied. The results indicate that the sizing of domestic T800 carbon fibers contain epoxy functional groups. With the formula optimized cyanate ester resin, the domestic T800 carbon fiber composite has greater mechanical property with the retention rate exceeding 74.8% at room-temperature with humidity, the retention of mechanical property is more than 57% at 200℃, and the glass transition temperature is 226℃. The composite exhibits excellent thermal mechanical and interfacial properties.
The influence of the particle size distribution on the strength of the coated Al2O3 parts was studied, through the size and distribution of the sintered neck. The powder was heated in situ by a UV laser, and the relationship between the sintered neck waist diameter and the particle diameter was obtained under an image measuring apparatus. A particle packing model was established, and the distribution of the sintered neck was corresponding to the particle coordination point, then the projected area ratio of the sintered neck that was broken in a certain section was calculated. As for the coated Al2O3 powder with the resin content of 2%(mass fraction), the results indicate that the sintered neck waist diameter increases from 40μm to 100μm as the particle diameter increases from 75μm to 375μm. The packing simulation results show that the projected area ratio decreases from 0.2557 to 0.0823, as the particle diameter increases from 75-107μm to 300-375μm, which is consistent with the experimentally measured tensile strength of the coated Al2O3 powder. The 70/100, 100/140 mesh powder are mixed to simulate based on the mass ratios of 0:10, 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, 10:0. The projected area ratio decreases from 0.1772 to 0.1264 and the porosity increases from 0.4511 to 0.4633. Considering the tensile strength and gas permeability, the optimization result is that the ratio is 7:3, the projected area ratio is 0.1481 and the porosity is 0.4596.
Isothermal constant strain thermal compression test was carried out by Gleeble-3500 thermal simulation test machine. Based on the experimental data, the flow behavior of Ti-22Al-24Nb-0.5Y alloy was studied. The factors affecting the flow stress of the alloy were analyzed by orthogonal test, and a constitutive model based on BP neural network was established. The results show that the main factors affecting the flow stress of the alloy successively are the strain rate, deformation temperature and strain. The flow stress of Ti-22Al-24Nb-0.5Y alloy in hot deformation is more sensitive to the strain rate and the deformation temperature. The deformation of the alloy is characterized by flow softening at low deformation temperature and high strain rate, but the deformation tends to steady flow with high deformation temperature and low strain rate. The high temperature constitutive model of alloy established by BP neural network has high accuracy. The correlation coefficient reaches 0.9949, the average relative error is 3.23%, the predictive value with the deviation within 10% data points reaches up to 98.79%, and the prediction model can be used as a constitutive relation for the finite element simulation in Ti2AlNb based alloy plastic forming process.
The crystal plasticity finite element simulation and experiment were used to study the orientation flow and strain stored energy accumulation of different initial texture components during cold rolling in non-oriented silicon steel. The results show that strong α and γ as well as weak λ deformation textures are formed after cold rolling. The recrystallization texture consists of γ, α, η and λ components, whose orientation densities are dependent on cold rolling reduction. With the increase of cold rolling reduction, λ recrystallization texture increases gradually, η recrystallization texture increases first and then decreases, γ recrystallization texture decreases first and then increases, while α recrystallization texture is weakened slightly. The strain stored energy during cold rolling has a significant dependence on initial grain orientation that the initial γ orientation has a similar or evidently higher strain stored energy accumulation rate below or above 50% reduction compared with initial α orientation, while λ keeps the lowest strain stored energy accumulation rate during cold rolling. Particularly, the different initial orientations rotating to an identical deformed orientation may cause an obvious difference in strain stored energy accumulation rate. The development of recrystallization texture in non-oriented silicon steel is determined by orientation flow and strain stored energy accumulation in various texture components during cold rolling.
A new high density alloy NiW750 was developed, which was based on the faced-center cubic solid solution structure and aging strengthening mechanism. Microstructure of the alloy was observed by SEM and TEM. The material characteristics under dynamic compressing loading were investigated by using the split Hopkinson pressure bar test. The comparison among the NiW750, ultra high strength steel G50 and tungsten 93WNiFe was also conducted.The results show that the NiW750 high density alloy has the best comprehensive properties among three materials. After aging at 750℃/5h, the tensile strength of NiW750 can achieve up to 1746MPa, while the impact toughness (akU) can achieve 113J/cm2. Under the condition of dynamic loading, the material shows strain rate hardening effect obviously as its dynamic flow stress can reach about 2250MPa. The adiabatic shear bands are formed within specimens in the direction of 45° to the central axis with a bandwidth of 80-150μm at the strain rate of about 5500s-1 and a wide transition zone, so as to avoid the premature emergence of the shear fracture.
The effect of surface roughness based on PS-PVD process on the structure of YSZ ceramic coating was studied. The influence mechanism of surface roughness on gas-phase deposition and structure formation of ceramic coating was discussed. YSZ ceramic coating was prepared by PS-PVD process on K417G superalloy prefabricated with NiCoCrAlYTa bond coating. The morphology and structural characteristics of PS-PVD YSZ coating were analyzed by means of SEM, roughness detector and 3D surface topography instrument. Substrate surface roughness has a great influence on PS-PVD coating structure. When the surface roughness of the substrate is Ra ≤ 2μm, 2μm < Ra < 6μm, and Ra ≥ 6μm, respectively, the coating roughness is in the range of 3.5-5, 6-10μm and 10-15μm, respectively. The diameter of cauliflower head increases with the increase of the surface roughness of substrate. The dP=38.5μm, d280S=25.5μm, d60S=38.7μm, d24S=102μm and dS=137μm. In the process of PS-PVD gas-phase deposition, surface roughness mainly affects the growth and formation of coating differential structures through shadow effect. With the increase of substrate surface roughness, YSZ ceramic coating is affected by shadow effect and the size of cauliflower head and the gap width between columnar structures are increased, forming a relatively loose structure.
The influence of cast steel shot-peening on the tensile properties of the second generation single crystal superalloy DD6 under 500, 600, 650℃ was investigated by SEM, X-ray and TEM. The results show that the shot-peening has no influence on the tensile strength of DD6 alloy at 500, 600, 650℃, and the yield strength is slightly increased, while the elongation and the shrinkage of cross section are remarkably decreased. The shot-peening DD6 alloy is ruptured after the flow stress rising to the highest point, and the cross section of fracture samples presents circle shape. The stress-strain curves of non-shot-peening DD6 alloy exhibit double stages feature, and the cross section of fracture samples presents ellipse shape.
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