应用CBR确定面心立方金属的表面弹性参量

首先从能量变分出发基于同时考虑应变梯度效应和表面效应的跨尺度力学理论,推导出表面能和表面弹性本构等基本关系,然后基于简单的准连续Cauchy-Born法则(CBR)建立一种确定表面能密度以及表面弹性参量的方法.进一步以面心立方(face-centre-cubic,FCC)金属为例,系统地获得了常用FCC金属表面弹性参量的数值,结果与他人应用分子动力学计算得到的结果相吻合.

带微裂纹物体的有效断裂韧性

按照等效介质的思想，引进有效表面能密度的概念，建立了带微裂纹物体有效断裂韧性的公式．具体计算了微裂纹群分别平行和垂直于宏观裂纹两种情况的减韧比．表明微裂纹群在产生应力屏蔽（或反屏蔽）效应的同时，也降低了材料的有效断裂韧性，减小了对宏观裂纹的扩展阻力．

考虑损伤时材料的断裂应力

工程结构的损伤分析、寿命预测及材料细观损伤机理与材料的强韧化研究 ,具有十分重要的工程意义 ,并具有广阔的发展前景。本文研究考虑损伤时材料的断裂应力 ,推导出了在表面能密度有限的情况下 。

Experimental study on mechanism of influence of laser energy density on surface quality of Ti-6Al-4V alloy in selective laser melting

This experiment obtained different laser energy density(LED) by changing SLM molding process parameters.The surface morphology, surface quality, and microstructure of as-fabricated samples were studied. The effects of scanning speed, hatching space, and laser power on surface quality were analyzed, and the optimal LED range for surface quality was determined. The results show that pores and spherical particles appear on the sample’s surface when low LED is applied, while there are lamellar structures on the sides of the samples. Cracks appear on the sample’s surface,and the splash phenomenon increases when a high LED is taken. At the same time, a large amount of unmelted powder adhered to the side of the sample. The surface quality is the best when the LED is 150-170 J/mm^(3). The preferred hatch space is currently 0.05-0.09 mm, the laser power is 200-350 W, and the average surface roughness value is(15.1±3) μm.The average surface hardness reaches HV404±HV3, higher than the forging standard range of HV340-HV395.Increasing the LED within the experiment range can increase the surface hardness, yet an excessively high LED will not further increase the surface hardness. The microstructure is composed of needle-like α’-phases with a length of about 20μm, in a crisscross ‘N’ shape, when the LED is low. The β-phase grain boundary is not obvious, and the secondaryphase volume fraction is high;when the LED is high, the α’-phase of the microstructure is in the form of coarse slats, and the secondary-phase is composed of a small amount of secondary α’-phase, the tertiary α’-phase and the fourth α’-phase disappear, and the volume fraction of the secondary-phase becomes low.

Quantum-mechanical study of effect of lattice defects on surface properties and copper activation of sphalerite surface

The electronic properties of sphalerite(110)surface bearing Fe,Mn and Cd impurities were calculated using density-functional theory,and the effects of impurities on the copper activation of sphalerite were investigated.Calculated results indicate that both Fe and Mn impurities narrow the band gap of sphalerite surface and lead to the Fermi level shifting to conduction band.Impurity levels composed of Fe 3d and Mn 3d orbital appearing in band gap are beneficial to electrons transfer from the valence band to the conduction band and promote the surface conductivity and the electrochemical activity.The results show that Fe and Mn impurities cannot be replaced by Cu atom,which reduces the exchange sites(Zn)for Cu atom,hence Fe-and Mn-bearing sphalerites are hard to be activated by copper.Cd impurity has little effect on electronic structure of sphalerite surface;however,Cd atom is easily replaced by Cu atom,and this is the reason why the Cd-bearing sphalerite can be easily floated.

Pseudopotential Density-Functional Calculations for Structures of Small CarbonClusters CN （N=2-8）

We introduce a first-principles density-functional theory,i.e.the finite-difference pseudopotential density- functional theory in real space and the Langevin molecular dynamics annealing technique,to the descriptions of structures and some properties of small carbon clusters(C_N,N=2～8).It is shown that the odd-numbered clusters have linear structures and most of the even-numbered clusters prefer cyclic structures.

HIGH EMISSION PERFORMANCE IMPREGNATED DISPENSER CATHODE

In order to obtain higher emission performance than that of a traditional M-type cathode, we have developed a new type impregnated dispenser cathode. The new cathode is impregnated with a new active substance with molar ratio of 26BaO·29SrO·8Sc2O3 ·7CaO·Al2O3 . This paper introduces the emission performance, surface active material, and work function of the new cathode. At 1100℃B , the DC current density and pulse current density are 30.6±1.0 A/cm2 and 171.6±2.8 A/cm2 , respectively, 2.1 and 5.4 times of that of an M-type cathode. The work function of the new cathode is 1.668± 0.002 eV. High concentration O-Al-Sc-Sr-Ba and O-Al-Sc-Ba are found in the pores and at pore edges, respectively. By comparing the emission performances and surface characteristics of as-polished and as-cleaned cathodes, it is proposed that, the emission around pore ends forms the major part of the total emission for the new cathodes.

Ultrathin Ni(OH)2 layer coupling with graphene for fast electron/ion transport in supercapacitor

Integration of fast electrochemical double-layer capacitance and large pseudocapacitance is a practical way to improve the overall capability of supercapacitor,yet remains challenging.Herein,an effective cyanogel synthetic strategy was demonstrated to prepare ultrathin Ni(OH)2 nanosheets coupling with conductive reduced graphene oxide(rGO)(rGO-Ni(OH)2)at ambient condition.Ultrathin Ni(OH)2 nanosheet with 3–4 layers of edge-sharing octahedral MO6 maximally exposes the active surface of Faradic reaction and promotes the ion diffusion,while the conductive rGO sheet boosts the electron transport during the reaction.Even at 30 A g−1,the optimal sample can deliver a specific capacitance of 1119.52 F g−1,and maintain 82.3%after 2000 cycles,demonstrating much higher electrochemical capability than bare Ni(OH)2 nanosheets.A maximum specific energy of 44.3 W h kg^−1(148.5 W kg^−1)is obtained,when assembled in a two-electrode system rGO-Ni(OH)2//rGO.This study provides an insight into efficient construction of two dimensional hybrid electrodes with high performance for the new-generation energy storage system.

Origin of the electrocatalytic oxygen evolution activity of nickel phosphides: in-situ electrochemical oxidation and Cr doping to achieve high performance

Zinc-air batteries(ZnABs) with high theoretical capacity and environmental benignity are the most promising candidates for next-generation electronics. However, their large-scale applications are greatly hindered due to the lack of high-efficient and cost-effective electrocatalysts. Transition metal phosphides(TMPs) have been reported as promising electrocatalysts. Notably,(Ni_(1-x)Cr_(x))_(2) P(0≤x≤0.15) is an unstable electrocatalyst, which undergoes in-situ electrochemical oxidation during the initial oxygen evolution reaction(OER) and even in the activation cycles, and is eventually converted to Cr-NiOOH serving as the actual OER active sites with high efficiency. Density functional theory(DFT) simulations and experimental results elucidate that the OER performance could be significantly promoted by the synergistic effect of surface engineering and electronic modulations by Cr doping and in-situ phase transformation. The constructed rechargeable ZnABs could stably cycle for more than 208 h at 5 m A cm^(-2), while the voltage degradation is negligible. Furthermore, the developed catalytic materials could be assembled into flexible and all-solid-state Zn ABs to power wearable electronics with high performance.

Activated pyrolysed bacterial cellulose as electrodes for supercapacitors

In this paper, the bacterial celluloses(BCs) were pyrolysed in nitrogen and then activated by KOH to form a porous three- dimension-network electrode material for supercapacitor applications. Activated pyrolysed bacterial cellulose(APBC) samples with enlarged specific surface area and enhanced specific capacitances were obtained. In order to optimize electrochemical properties, APBC samples with different alkali-to-carbon ratios of 1, 2 and 3 were tested in two electrodes symmetrical capacitors. The optimized APBC sample holds the highest specific capacitance of 241.8 F/g, and the energy density of which is 5 times higher than that of PBC even at a current density of 5 A/g. This work presents a successful practice of preparing electrode material from environment-friendly biomass, bacterial cellulose.

Revealing the interface-rectifying functions of a Li-cyanonaphthalene prelithiation system for SiO electrode

Chemical prelithiation is regarded as a crucial method for improving the initial Coulombic efficiency(ICE)of Li-storage anodes.Herein,a substituent-engineered Li-cyanonaphthalene chemical prelithiation system is designed to simultaneously enhance the ICE and construct a multifunctional interfacial film for SiO electrodes.X-ray photoelectron spectroscopy(XPS),electron energy-loss spectroscopy(EELS),nuclear magnetic resonance(NMR)spectroscopy and atomic force microscopy(AFM)prove that the Licyanonaphthalene prelithiation reagent facilitates the formation of a rectified solid electrolyte interface(SEI)film in two ways:(1)generation of a gradient SEI film with an organic outer layer(dense Ncontaining organics,ROCO_(2)Li)and an inorganic LiF-enriched inner layer;(2)homogenization of the horizontal distribution of the composition,mechanical properties and surface potential.As a result,the prelithiated SiO electrode exhibits an ICE above 100%,enhanced CEs during cycling,better cycle stability and inhibition of lithium dendrite formation in the overcharged state.Notably,the prelithiated hard carbon/SiO(9:1)‖LHCoO_(2) cell displays an enhancement in the energy density of 62.3%.

In-depth study on aminolysis of poly(ε-caprolactone): Back to the fundamentals

The aminolysis can effectively introduce primary amine （- quent surface fiiofunctionalization reactions. However, less NH2） groups onto polyester materials, enabling a variety of subse- attention has been paid to the basic knowledge of aminolysis reac- tion in terms of reaction kinetics and its influences on materials properties. In this study, taking the widely used poly（e-caprolactone） （PCL） as a typical example, the influences of diamines and solvent property on the surface -NH2 density are firstly assessed by using X-ray photoelectron spectroscopy （XPS） and colorimetric analysis. Results show that smaller dia- mine molecules and nonpolar alcohols could accelerate the reaction. The reaction kinetics with 1,6-hexanediamine is further investigated as a function of temperature, reaction time, and diamine concentration. During the initial stage, the reaction shows a 1^st order kinetics with the diamine concentration and has an activation energy of 54.5 kJ/mol. Ionization state of the -NH2 groups on the PCL surface is determined, revealing that the pKa of -NH3^＋ （〈5） is much lower than that of the corresponding diamine molecules in solution. After aminolysis, surface hydrophilicity of PCL membrane is significantly enhanced, while surface elastic modulus and average molecular weight are decreased to some extent, and others such as weight, surface mor- phology and bulk mechanical strength are not apparently changed. The introduced -NH2 groups are found to be largely lost at 37 ℃, but can be mostly maintained at low temperature.

Hole effective mass in strained Si (111)

The directional, averaged, and density-of-states effective masses of holes have been calculated for strained Si/(111)Si1-xGex. The results for the directional effective mass show that the effect of strain makes the constant energy surface of "heavy" holes more obvious warping than that in relaxed Si. The [111] and [110] directional effective masses of "heavy" holes decrease significantly under strain. It is found that the averaged effective mass of "heavy" holes decreases with increasing Ge fraction, while that of "light" holes increases. The traditional concepts of heavy and light holes become insignificant when Ge fraction is close to 0.4. The strain effect monotonically reduces the density-of-states effective mass at 218, 300 and 393 K, respectively.