作者机构：
[毛聪; 张健; 龙春光; 华熳煜] Key Lab. of Lightweight and Reliability Technol. for Eng. Vehicle, Edu. Department of Hunan Province, Institute of Automobile and Mechanical Engineering, Changsha University of Science and Technology, Changsha 410114, China;[周惦武] State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, Changsha 410082, China;[张健] Hunan Provincial Key Laboratory of Materials Protection for Electric Power and Transportation, School of Chemistry and Biological Engineering, Changsha University of Science and Technology, Changsha 410004, China
通讯机构：
Key Lab. of Lightweight and Reliability Technol. for Eng. Vehicle, Edu. Department of Hunan Province, Institute of Automobile and Mechanical Engineering, Changsha University of Science and Technology, China
摘要：
Nanofluid minimum quantity lubrication (MQL) method was used in the grinding process to replace conventional fluid grinding for overcoming ecological and economical problems. Although previous researchers have studied the lubricating and cooling performance of nanofluid MQL grinding, a systematical analysis of the effect of nanofluid parameters on grinding performance has not been done yet. In this study, nanofluid surface grinding experiment with MQL method under different nanofluid parameters was accomplished. The grinding properties, such as grinding force, grinding force ratio, grinding temperature, and ground surface roughness were investigated. It is found that the lubricating and cooling performance in the grinding zone are improved with the increase of the nanoparticle concentration. Therefore, nanofluid MQL grinding with higher concentration nanoparticle has lower grinding force, grinding temperature, and surface roughness in comparison with lower concentration nanoparticle. When the diameter of nanoparticle increases, tangential grinding force decreases slightly, and the peak grinding temperature is similar. However, the surface finish is deteriorated with the increase of the diameter of nanoparticle. The experimental results also show that the lubricating performance of water-based nanofluid is worse than that of oil-based nanofluid, but the cooling effect is just reverse.
关键词：
Metal hydrides;Electronic properties;Enthalpy;Thermodynamic properties
摘要：
The energetic and electronic properties of MgH2 co-doped with Ti and F are investigated using first-principles calculations based on density functional theory. The calculation results show that incorporation of Ti combined with F atoms into MgH2 lattice is energetically favorable relative to single incorporation of Ti atom. After dehydrogenation, the co-doped Ti and F in MgH2 preferably generate TiH2 and MgF2, respectively. Comparatively, the combined effect of Ti and F in improving the dehydrogenation properties of MgH2 is superior to that of pure Ti. These results provide a reasonable explanation for experimental observations. Analysis of electronic structures suggests the enhanced dehydrogenation properties of doped MgH2 can be attributed to the weakened bonding interactions between Mg and H due to foreign species doping.
摘要：
Method of transit priority signal control of isolated intersection is researched in the paper for an intersection at east door south road and spring breeze road in Shenzheng. In which, the delay of each passenger is used as new index to evaluate the control effect. The results show that the method of transit priority signal control of isolated intersection is better than the before, which could reduce the delay and give expression to the ideal "people first".
关键词：
Ab initio calculation;Dehydrogenation property;Electronic structure;Hydrogen storage materials;Stability
摘要：
Mg3MNi2 (M = Al, Ti, Mn) ternary intermetallic compounds with cubic structure are a new type of potential hydrogen storage alloys. Using ab initio density functional theory (DFT) calculations, the energetics and electronic structures of Mg3MNi2 (M = Al, Ti, Mn) compounds are systematically investigated. The optimized structural parameters including lattice constants and internal atomic positions are close to experimental data determined from X-ray powder diffraction. The calculated results of formation enthalpy ΔHform show that the stabilities of cubic Mg3MNi2 (M = Al, Ti, Mn) compound, compared with hexagonal Mg2Ni, increase in the order of Mg3MnNi2, Mg2Ni, Mg3TiNi2 and Mg3AlNi2, whereas the stabilities of their saturated Mg3MNi2H3 (M = Al, Ti, Mn) hydrides, compared with monoclinic Mg2NiH4, decrease in the order of Mg2NiH4, Mg3AlNi2H3, Mg3TiNi2H3 and Mg3MnNi2H3. Further calculations of hydrogen desorption enthalpy ΔHdes indicate that these cubic Mg3MNi2 (M = Al, Ti, Mn) compounds possess promising dehydrogenation properties for their relatively lower ΔHdes values. Among of them, the dehydrogenation ability of Mg3TiNi2 is the most pronounced. Analysis of electronic structures suggests that the strong covalent bonding interactions between Ni and M within cubic Mg3MNi2 (M = Al, Ti, Mn) are dominant and directly control the structural stabilities of these compounds.
作者机构：
[张健; 龙春光; 邵毅敏] Institute of Automobile and Mechanical Engineering, Changsha University of Science and Technology, Changsha 410114, China;[黄雅妮; 彭平] College of Materials Science and Engineering, Hunan University, Changsha 410082, China;[周惦武] State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, Changsha 410082, China
通讯机构：
[Zhang, J.] I;Institute of Automobile and Mechanical Engineering, Changsha University of Science and Technology, China
作者机构：
[邵毅敏; 张健; 华熳煜] Institute of Automobile and Mechanical Engineering, Changsha University of Science and Technology, Changsha 410114, China;[周惦武] State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, Changsha 410082, China;[黄雅妮; 彭平] College of Materials Science and Engineering, Hunan University, Changsha 410082, China
通讯机构：
Institute of Automobile and Mechanical Engineering, Changsha University of Science and Technology, China
摘要：
Mg2NiH4, with fast sorption kinetics, is considered to be a promising hydrogen storage material. However, its hydrogen desorption enthalpy is too high for practical applications. In this paper, first-principles calculations based on density functional theory (DFT) were performed to systematically study the effects of Al doping on dehydrogenation properties of Mg2NiH4, and the underlying dehydrogenation mechanism was investigated. The energetic calculations reveal that partial component substitution of Mg by Al results in a stabilization of the alloy Mg2Ni and a destabilization of the hydride Mg2NiH4, which significantly alters the hydrogen desorption enthalpy ΔHdes for the reaction Mg2NiH4 → Mg2Ni + 2H2. A desirable enthalpy value of ∼0.4 eV/H2 for application can be obtained for a doping level of x ≥ 0.35 in Mg2−xAlxNi alloy. The stability calculations by considering possible decompositions indicate that the Al-doped Mg2Ni and Mg2NiH4 exhibit thermodynamically unstable with respect to phase segregation, which explains well the experimental results that these doped materials are multiphase systems. The dehydrogenation reaction of Al-doped Mg2NiH4 is energetically favorable to perform from a metastable hydrogenated state to a multiphase dehydrogenated state composed of Mg2Ni and Mg3AlNi2 as well as NiAl intermetallics. Further analysis of density of states (DOS) suggests the improving of dehydrogenation properties of Al-doped Mg2NiH4 can be attributed to the weakened Mg–Ni and Ni–H interactions and the decreasing bonding electrons number below Fermi level. The mechanistic understanding gained from this study can be applied to the selection and optimization of dopants for designing better hydrogen storage materials.
摘要：
Compared to surface grinding, wire-electrodischarge machining (WEDM) is competitive because WEDM allows the machining of any type of conductive material, regardless of its hardness. Nevertheless, WEDM is not preferred for final machining due to the existence of the process-induced damaged layers. In this study, the damaged layers formed in hardened AISI 52100 steel by surface grinding and WEDM are researched and compared. It is found that the damaged layers for both grinding and WEDM are composed of the white layer and dark layer, and the white layer possesses a highly refined grain structure compared to the bulk material. The retained austenite content of the ground white layer is lower than that of the unmachined material, while WEDM white layer has much high retained austenite volume fraction. The microhardness of the ground white layer is higher than that of the WEDM one. High residual tensile stresses are observed in the ground surface, and slight compressive stresses are observed just below the surface. WEDM generates residual tensile stresses in the surface. It is also found that mechanical deformation plays an important role in ground damaged layers compared to WEDM ones, where thermal effects are more dominant.
关键词：
hydrogen storage materials;density functional theory;electronic structure;enthalpy of formation
摘要：
Mg<inf>2</inf>FeH<inf>6</inf>, which has the highest volumetric hydrogen density, is considered a promising hydrogen storage material. Within the framework of the density functional theory, the crystal structure, physical properties, electronic structure and formation capacity of Mg <inf>2</inf>FeH<inf>6</inf> complex hydride have been investigated. The optimized structural parameters correspond closely with the experimental data from X-ray and neutron powder diffraction measurements. A detailed study of the electronic structures, including the energy band, density of states (DOS) and charge density distribution, reveals the orbital hybridization and bonding characteristics within this hydride. It was shown that Mg<inf>2</inf>FeH <inf>6</inf> is a semiconductor with the energy gap of ca. 2.3347 eV, and that a mixed ionic-covalent bond between Fe and H in FeH<inf>6</inf> complexes is embedded in the matrix of Mg<sup>2+</sup> cations. The calculated formation enthalpies of Mg<inf>2</inf>FeH<inf>6</inf> , based on the possible synthesis routes, indicate that optimum conditions are achieved if this hydride is fabricated from pure elements, and that the preparation of other compounds would lead to inferior synthesis.
