- 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)
The AZ91D magnesium alloy samples were scanned by millisecond pulse Nd:YAG laser under high pure argon protection. The surface morphology, microstructure and composition of the treated magnesium alloy were studied by X-ray diffraction, optical microscopy, scanning electron microscopy, atomic force microscopy. In addition, the corrosion surface which was corroded using simulated body fluid and the mass fraction of 3.5%NaCl solution was observed and material corrosion rate was calculated. The results show that, at the same corrosion time, compared with the untreated samples, the surface corrosion resistance is improved by the enrichment of Al at the irradiated surface by the joint effect of the combination of refined homogeneous microstructure of α-Mg phase and β-Mg17Al12 phase and the selective vaporization and the chemical composition of base metal in the laser-treated AZ91D alloy; the solidification equation is obtained by calculating the relation between the size of the dendrite cell and the cooling rate in laser melting zone.
The precipitation behavior and distribution of second phase particles in conventional grain-oriented silicon steel during manufacturing process were observed by field emission scanning electron microscopy, and the average particle size, the areal particle density, and the Zener factor were statistically analyzed. The results show that the samples mainly contain two kinds of precipitates:A class is the (Cu, Mn)S composite precipitates with the average size of 1μm; B class is the Cu2S precipitates with the size of 10-30nm, the key inhibition effect is produced by Cu2S. Hot rolling leads to a large amount of fine second phase particles precipitation, which has the minimum average particle size and the highest areal density; in the manufacturing process before high temperature annealing, the average particle size is increasing and the areal density is decreasing; in the process of high temperature annealing, with the decrease of volume fraction of precipitates, the inhibition ability exhibits reducing trend, obvious aggregation occurs at 960℃, secondary recrystallization will happen when Zener factor A decreases below the critical value of 0.19nm-1, and the residual particles will not produce valid inhibition effect.
The wetting of TA2 pure Ti by two industrial grade Al alloys (i.e., 6061 Al and 4043 Al alloys) was studied by using the modified sessile drop method at 600, 650, 700℃ under high vacuum. The results show Al/Ti system is a typical reactive wetting, the small amount of alloying element Si in the Al alloys can cause significant enrichment at liquid/solid interface and satisfy thermodynamic condition; the formation of the Si-rich phase (Ti7Al5Si12) strangling material exchange at triple line zone; Ti7Al5Si12 decomposition and Al3Ti formation can remove the oxide film and promote wetting; the spreading dynamics can be described by reaction product control model, further the whole wetting behavior can be divided into two stages:the first stage for the nonlinear spreading and the second stage forthe linear spreading; the activation energies which are 56kJ/mol, 47kJ/mol for nonlinear stages of 6061 Al and 4043 Al alloys, and 112kJ/mol for linear stage of 6061 Al alloys, respectively, Ti7Al5Si12 decomposition is corresponding to the nonlinear spreading.
To study the thermal aging of nuclear primary pipe material 316LN stainless steel weld, accelerated thermal aging experiment was performed at 400℃ for 15000h. Microstructure evolution of weld after aging was investigated by TEM and HREM. Impact properties of weld thermally aged at different time was measured by Charpy impact test. Meanwhile, taking Charpy impact energy as the standard of thermal aging embrittlement, the thermal kinetics formula was obtained by the fitting method. Finally, the Charpy impact properties of the weld during 60 years of service at the actual operation temperature were estimated by the thermal kinetics formula. The results indicate that the spinodal decomposition occurs in the ferrite of the weld after thermal aging at 400℃ for 1000h, results in α (Fe-rich) and α'(Cr-rich) phases, and meanwhile, the G-phase is precipitated in the ferrite; the spinodal decomposition and the G-phase precipitation lead to the decrease in the impact energy of weld as time prolongs; the prediction results show that the Charpy impact energy of weld decreases quickly in the early 25 years, and then undergoes a slow decrease during the subsequent operation process.
Graft copolymers of PLA-g-MAH, PLA-g-GMA and PLA-co-MAH/GMA were prepared by means of melt grafting. The structure of the graft copolymers were characterized by FTIR.Wood flour/PLA composites were prepared by injection molding with three kinds of graft copolymers as compatibilizers, and the fractured morphology of composites was investigated by scanning electron microscope (SEM). Results show that there is no obvious phase interface between wood flour and PLA, which indicating the interfacial compatibility of wood flour/PLA composites is improved after adding different graft copolymers. The determination results of mechanical properties, processing flowability and dynamic rheological property of composites prepared with different graft copolymers reveal that, compared to the composite without compatibilizer, the tensile strength and impact strength of wood flour/PLA composites are increased by 9.54% and 7.23% respectively, and the equilibrium torque, shear heat, storage modulus and complex viscosity are all increased after adding maleic anhydride/glycidyl methacrylate cografted polylactic acid.
Carbon fiber is composed of crystallite and amorphous carbon. The X-ray diffraction (XRD) and Raman spectroscopy were used to investigate the influencing mechanism of the microstructure of crystallites of polyacrylonitrile (PAN)-based carbon fibers on tensile strength. The results show that the crystallinity, the degree of graphitization, the degree of crystallites structural disorder and the crystallite size have obvious effects on tensile strength. The larger the crystallinity and the degree of graphitization, the larger the tensile strength; the smaller the degree of crystallites structural disorder, the larger the tensile strength; the larger the crystallite size, the smaller the tensile strength. Comparing T300 with T700, the increment of tensile strength, which is caused by the increase of the crystallinity and the degree of graphitization, and the decrease of the degree of crystallites structural disorder, is larger than the decrement of tensile strength, which is caused by the increase of the crystallite size. Therefore, the tensile strength of T700 is larger than that of T300, and the same with that the tensile strength of T800 is larger than that of T700. When M35J is compared with M40J, the increment of tensile strength, which is caused by the increase of the crystallinity and the degree of graphitization, and the decrease of the degree of crystallites structural disorder, is smaller than the decrement of tensile strength, which is caused by the increase of the crystallite size. Therefore, the tensile strength of M40J is smaller than that of M35J, and the same with that the tensile strength of M46J is smaller than that of M40J. In M35J, M40J and M46J, the bigger crystallite size is a crucial factor that affects the tensile strength.
Short glass fiber reinforced polyamide 10T (SGF/PA10T) composites were prepared by melt blending method, and the thermal-oxidative aging properties of SGF/PA10T composites at 240℃ were characterized by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis(DMA), FT-IR and mechanical properties test. The results show that the crystallization onset temperature of SGF/PA10T increases, the interfacial interaction between glass fiber and PA10T matrix is weakened, and damping capacity decreases during the thermal-oxygen aging process. With the increase of thermal-oxygen aging time, the glass transition temperature increases first and then decreases. Arrhenius equation was used to determine the glass transition activation energy of SGF/PA10T, and the results show that the mobility of molecular chain is changed and PA10T molecular chains are slight cross-linked in preliminary aging stage. At the same time, the thermal-oxygen can significantly reduce the mechanical properties of SGF/PA10T composites, after age at 240℃ for 50d, the tensile strength, flexural strength and impact strength retention rates are 18.4%, 9.8% and 37.7% respectively.
The influence of thermal-oxidative aging on flexural property of carbon fiber bismaleimide resin composites was investigated via three point flexural test. The mass loss behavior, fracture morphology, dynamic mechanical property and IR spectrum of the composites were analyzed at different aging time. The results show that with the increase of aging time, the mass loss rate at 100℃ aging temperature gradually tends to stabilize and the mass loss rate at 180℃ aging temperature gradually increases. There is only physical aging at 100℃ aging temperature and no new substance is generated; but at the aging temperature 180℃, the chemical aging occurs and results in thermal aging and oxidation reactions, causing the degradation of matrix and interface properties. The influence of thermal-oxidative aging on flexural strength of composites is greater than flexural modulus.
C/C-SiC composites were prepared by the combined process of chemical vapor infiltration (CVI) and gaseous silicon infiltration (GSI) using C/C green body with the density of 1.0g/cm3. Effect of CVI C/C-SiC intermediate composites' density on the phase composition, microstructure and mechanical properties of CVI-GSI C/C-SiC composites was studied. The results show that as the CVI C/C-SiC intermediate composites' density increases, the residual C content increases and residual Si content decreases in the CVI-GSI C/C-SiC composites, the SiC content increases first and then decreases, and the density of CVI-GSI C/C-SiC composites increases first and then decreases; as the CVI C/C-SiC in termediate composites' density is increased from 1.27g/cm3 to 1.63g/cm3, the mechanical properties of CVI-GSI C/C-SiC composites increase at first, which then decrease with the further increasing of CVI-C/C-SiC composites' density. Specifically, when the CVI C/C-SiC composites density is 1.42g/cm3, the prepared CVI-GSI C/C-SiC composites has the best mechanical properties, with flexure strength, flexure modulus and fracture toughness of 247.50MPa, 25.63GPa and 10.08MPa·m1/2, respectively.
The low-velocity impact and compression after impact (CAI) properties of three-dimensional (3D) five-directional carbon fiber/epoxy resin braided composites were experimentally investigated. Specimens prepared with different braiding angles were tested at the same impact energy level. Residual post-impact mechanical properties of the different configurations were characterized by compression after impact tests. Results show that the specimens with bigger braiding angle sustain higher peak loads, and smaller impact damage area, mainly attributes to a more compact space construction. The CAI strength and damage mechanism are found to be mainly dependent on the axial support of the braiding fiber tows. With the increase of braiding angle, the CAI strength decreases, and the damage mode of the composites is changed from transverse fracture to shear failure.
Carbon nanotubes(CNTs) with uniform diameters and big length-diameter ratio were formedboth on the surface and the inner pores of nickel foam by microwave-assisted heating method, using nickel foam treated with HCl as catalyst precursor and auxiliary heating material, phenanthrene as the carbon source. The micro morphology and microstructure were characterized by SEM and XRD methods. Effect of the structure of nickel foam, concentration of HCl and micro-assisted heating time on the preparation of CNTs was studied, the mechanism for CNTs growth was also recommended. The results show that, when the concentration of HCl is 6mol·L-1, microwave-assisted heating time is 30s, the diameter of CNTs is around 30nm, the length is up to micrometer.
ZrW2O8 powders were prepared by sol-gel method with PVP as the additive. The effect of PVP on the morphology was studied and negative thermal expansion property of ZrW2O8 powders was also investigated. The precursor of ZrW2O8 was analysized by thermogravimetric and differential scanning calorimetry (TG-DSC). The structure and morphology of the resulting powder were characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. The results show that the resulting powder is single cubic α-ZrW2O8 phase. The addition of PVP can effectively change the morphology of the powder, with the increasing amount of PVP, morphology of the particles changes from irregular aggregates to rod-like, fan-shaped and short rod particles. The results of in-situ X-ray diffraction measurement indicate that ZrW2O8 powder prepared with the addition of PVP has good negative thermal expansion property.
To improve the poor thermal stability and electrolyte wettability of polyolefin-based separators, a high performance zeolite-based separator was prepared by a sintering process using zeolite particles, silica sol and ethylenediamine tetraacetic acid. The results show that compared with PE separator, the as-prepared zeolite separator exhibits well-developed microstructure superior thermal resistance and excellent liquid electrolyte wettability; the present separator has almost no thermal shrinkage after the heat treatment at 160℃ for 0.5h, while PE separator shows 100% thermal shrinkage under the same condition. Moreover, the electrolyte contact angle of zeolite separator is about 0±, while that of PE separator reaches 35°. Based on the above advantages, the zeolite separator shows better electrochemical performances, such as the discharge C-rate capability and cycling performance, as compared to the commercialized PE separator.
Integrating graphene into micro-and nano-devices is a critical step for its application in many fields. Graphene-a type of two-dimensional nanomaterials was assembled by dielectrophoresis(DEP) and the influence of the DEP process parameters including the magnitude of the applied voltage, the concentration of the graphene suspension, and the duration of the electric field was investigated. Results show that the quantity of the assembled graphene increases with increasing these parameter values, and the concentration of the graphene suspension is the most significant factor. I-V curve of the assembled graphene presents a good linearity and the electrical resistance of the samples ranges from several kΩ to several hundred kΩ, depending on the quantity of the assembled graphene. This indicates that there exists a high contact resistance between graphene and metal electrodes. The contact resistance of graphene can be reduced efficiently by local joule heating, and the contact resistance is reduced at its most by 47.91% when the applied voltage is 3.6V.
The precursor of titanium dioxide nanotubes(TiO2-NTs) was obtained by alkaline hydrothermal approach, which was supported by graphene oxide to form titanium dioxide nanotubes/reduced graphene oxide composite(TiO2-NTs/rGO). The composite was characterized by X-ray diffraction(XRD), transmission electron microscope (TEM) and electrochemical measurements. The results show that the crystalline phase of TiO2-NTs in composite is TiO2(B) with diameter of about 25-30nm. Compared with pure TiO2-NTs, the rate performance and cycle life of composite are improved remarkablely by loading on graphene. When discharged at the rate of 1C(335mA/g), the initial discharge capacity of TiO2-NTs/rGO and TiO2-NTs are 258.5mAh/g and 214.9mAh/g, respectively. The charge transfer resistance of composite is smaller than pure TiO2-NTs characterized by electrochemical impedance spectroscopy.
The reduced graphene oxides(rGO) loaded-nano ZnS nanoparticles were fabricated by microwave heating method and by ion exchanged reaction reduced graphene oxides(rGO) loaded-nano ZnS/CuS heterostructures were obtained. The structure, morphology were characterized via scanning electron microscopy(SEM), transmission electron microscopy(TEM) and X-ray diffraction pattern(XRD). The effect of the mass fraction of graphene oxides, sulfur source and microwave heating time on the morphology and photocatalyitc performance were discussed. The results show that graphene uniformly loaded-nano ZnS/CuS heterostructures are obtained on the condition of graphene mass fraction of 10%, thioacetamide acting as sulfur source, microwave heating time is 30min. rGO-loaded nano ZnS/CuS heterostructures nanoparticles enhance photocatalytic performance with 81.2% decomposition of MO in 150min under visible light, demonstrating the excellent photocatalytic performance. The high visible photocatalytic performances are attributed to photoinduced interfacial charge transfer in the nano heterostructures and their further separation and transfer by rGO.
The direct foaming method combined with gelcasting was employed to prepare mullite ceramic foam. Triacetin, polyimide and hydroxypropyl cellulose were creatively proposed as gelling agent for gelcasting process, respectively. The influence of gelling agent on rheological properties and the correlation rule with the curing time were studied. The results show that different kinds of gelling agent have different influence on rheological properties. It is considered that the rheological properties have significant influence on the curing time. Ameliorating the thixotropy, improving the rate of viscosity growth, and enlarging the linear viscoelastic domain of foam slurry are conducive to shorten the curing time of foam slurry. Among these three gelling agents, the triacetin obtains the optimal effects, the initial curing time and curing time of foam slurry is both shortest.
Graphene is an ideal material for energy storage application as its excellent mechanical and physical properties. 3D printed graphene materials will be widely applied in energy storage field for its precisely controllable structure and it is easy to realize large-scale preparation. In this paper, the progress of 3D printed graphene materials synthesis technology and its application in energy storage field were reviewed. The viscosity and printability of graphene ink are key factors for realizing graphene 3D printing. Scalable preparation of graphene ink with facile process, controllable concentration and additive free will be the research focus of graphene 3D printing technologies in the future. The integrated printing of graphene energy storage devices such as graphene supercapacitor, lithium-sulfur battery and lithium ion battery is the development direction in this area.
Cyclodextrin (CD) molecules have a toroidal shape with a hydrophobic inner cavity and a hydrophilic exterior. The hydrophobic inner cavity can enable CD molecules to show high molecular selectivity and enrichment capability, and the hydrophilic exterior can make CD have high solubility in various solvents. On the other hand, because of the large theoretical surface areas and excellent electrochemical properties of carbon nanomaterials, they have important potential applications in electroanalytical chemistry. However, pure carbon nanomaterials usually are insoluble in solvents. Thus, it's of great significance to functionalize carbon nanomaterials with CD:CD not only improves the dispersity of carbon nanomaterials, but also enables high molecular selectivity and enrichment capacity, and hence shows extremely high electroanalytical capability. This review shows the methods and mechanism for preparing CD functionalized carbon nanomaterials (carbon nanotube, graphene, hollow carbon sphere, etc.) and their applications in electroanalytical chemistry. Finally, some critical challenges and prospects in this field were also briefly discussed.
Environment-friendly non-copper coated solid wire is the main developing trend for gas shielded solid wires, whereas wear of contact tube limits their wide application. The effect of nano-modified coatings and welding process parameters on wear of contact tube for non-copper coated solid wires was reviewed. It was found that the wear of contact tube can be reduced due to the formation of tribo-films on the rubbing surfaces of welding wires against contact tube; it is feasible to decrease contact tube wear when non-copper coated solid wires are coated with nano-modified lubricants, thereby displaying excellent lubricating and thermal or electrical conduction characteristics. The wear of contact tube increases with the increase of welding current. The wear of contact tube is worse in direct-current electrode positive (DCEP) than in direct-current electrode negative (DCEN). Arc ablation and electrical erosion are the dominant wear mechanisms of contact tube.
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