FULL-ELECTRON CALCULATION OF α-LaNi5H0.5 and β-LaNi5H3

在全电子水平上,基于广义梯度近似密度泛函和全势线性缀加平面波方法,计算出了LaNi5储氢合金固溶相α-LaNi5H0.5与中间相β-LaNi5H3的晶体结构、态密度和电荷密度等特征.在α相区域中,通过对5种不同间隙位置的能量计算得到12n位最稳定;点阵常数a随着H原子增多而增大,而c基本为一常数.在α→β相区域中,a值随着H原子的增多进一步增大,而c值增大相对较小.计算值与实验结果一致.     

Preparation of colloidal Sb_2O_5 and its stability

1　INTRODUCTIONColloidalantimony pentoxideisanewinorganicflameretardant .Itcanbeusedinrubber,plastics,fiber ,textile ,carpet,paint ,paperandprintedcircuitboardbe causeofitsflameretardingabilityandotherexcellentpropertiessuchashighdispersion ,lowcoloringintensityandhighheat stability[15] .Althoughmoreandmoreap plicationsofcolloidalantimonypentoxidearefoundintheindustry,therearelackofdetailedstudiesonprepara tionandstabilityofcolloidalantimonypentoxideex ceptsomepatentsabouttechnologicalproc…     

Orientation relationship and interfacial structure between ζ-Ti5Si3 precipitates and γ-TiAl intermetallics

The orientation relationship (OR) and the interface structure between Ti₅Si₃ precipitates and the γ-TiAl phase have been investigated systematically. The habit plane of Ti₅Si₃ in TiAl was determined to be (0001)_ζ6(111)_γ. However, there is no low-index direction of the two phases parallel to each other in the plane. This “abnormal” OR has been predicted precisely from a recently developed geometrical method, in which the overlap of reciprocal lattice points of two adjoining crystals is utilized to obtain the optimum OR. In spite of the significant difference in crystal structure between TiAl and Ti₅Si₃, the interface was found to be semi-coherent with good matching and has the largest possible displacement shift complete lattice corresponding to the bicrystal. The energy of the interface is also discussed. The translational state between the two lattices and the chemistry of the terminating plane of Ti₅Si₃ have been determined by using high-resolution transmission electron microscopy.     

Hydrothermal synthesis and magnetic property of NaV_2O_5 nanorods

1　ＩＮＴＲＯＤＵＣＴＩＯＮＲｅｃｅｎｔｌｙ ,ｏｎｅ ｄｉｍｅｎｓｉｏｎａｌ (1Ｄ )ｎａｎｏｓｔｒｃｔｕｒｅｍａｔｅｒｉａｌｓａｒｅｔｈｅｆｏｃｕｓｏｆｃｏｎｓｉｄｅｒａｂｌｅｉｎｔｅｒｅｓｔ ,ｓｉｎｃｅｔｈｅｓｅｍａｔｅｒｉａｌｓｓｈｏｗｄｉｆｆｅｒｅｎｔｐｈｙｓｉｃａｌａｎｄｃｈｅｍｉｃａｌｐｒｏｐｅｒｔｉｅｓｔｏｔｈｅｉｒｂｕｌｋｃｏｕｎｔｅｒｐａｒｔｓ[1] .Ｂｕｔｗｅｌｌ ｄｅｆｉｎｅｄｓｔｒｕｃｔｕｒｅｓｏｆｔｈｉｓｓｃａｌｅａｒｅｄｉｆｆｉｃｕｌｔｔｏｏｂｔａｉｎｂｅｃａｕｓｅｎｅｉｔｈ…     

Theoretical analysis of β-LaNi5Hx（5≤x≤8）： structure and energetics

The calculations of total energy, band structure, and electronic density of states and Mulliken population analysis of β-LaNi5Hx（5≤x≤8） were performed by adopting the method of total energy based on the density functional theory. The augmented plane wave function was selected as the basis set in combination with ultra-soft pseudo-potential technology. The influence of the amount of H absorbed in alloys was discussed in terms of geometry, electronic structure and thermodynamic derived from calculated results. The results show that the amount of H absorbed and the preferred site occupation of the absorbed hydrogen atoms were controlled by the position of H- bands and the energy gap between H-bands and conduction bands. The β-phase hydrides of LaNi5 are most stable when hydrogen atom capacity coating in the range of 6 ～ 7.     

Relationship between cooling rate and electrochemical performance of melt-spun AB_5 alloy

1　INTRODUCTIONNi/MHsecondarybatterieshaverapidlybeendevelopedandgraduallysubstitutedforNi/Cdbatter iesintherecentdecadeduetoitshighspecificenergydensityandhavingnopoisonouselementcadmium .TheactivematerialofnegativeelectrodewidelyusedinNi/MHsecondarybatteriesisAB5 typehydrogenstoragealloynowadays .However ,itisstillneededtoimprovethecomprehensive propertiesofAB5 typehydrogenstoragealloyforprolongingtheservicelifeofNi/MHbatteries .Anormalmethodtoimprovethecomprehensivepropertiesofthe…     

Electron beam welding of Re and BT5-1 titanium alloy

Based on the binary alloy phase diagram of Re-Ti, the weldability of Re and BT5-1 titanium alloy was analyzed. Using two methods of direct electron beam welding （EBW-D） and intergradafion electron beam welding （EBW-I）, Re and BT5-1 was welded. Experimental results show that the joint figuration of EBW-D between Re and BT5-1 is not fine, and the joint is inclined to brittleness rupture. The joint figuration of EBW-I between Re and BT5-1 is fine. No cracking and other disfigures occur in the intergradation joint. The element distribution of Re, Me, and Ti in the weld metal is progressional diversification.     

Ordered phases and texture in spray-formed Fe–5 wt%Si

Fe–Si alloys have excellent soft magnetic properties, especially around 12 at.% Si. However, their industrial applications are limited because they lack the ductility required in rolling operations for the fabrication of thin sheets, thus leading to cracking. The brittleness of high silicon alloys is caused by order–disorder reactions at low temperatures. This work involved an analysis of the effect of heat treatment on the crystalline structure of thin sheets of Fe–5 wt%Si alloy obtained in a two-step fabrication route: (1) spray forming of Fe–3.5%Si + 2.0%Sip composite and (2) rolling and heat treatment of the composite to dissolve the silicon and homogenize its content across the thickness of sheet samples. Structural and microstructural analyses indicated the success in fabricating thin sheets of Fe–5 wt%Si alloys with such strategy. The presence of the ordered B2 phase had an important effect on the texture development and therefore on the magnetic properties of these alloys.     

Microstructure and mechanical properties of spot welded Al–5·5Mg–0·3Cu alloy

Abstract

The influences of spot welding on the microstructure and mechanical properties of an Al–5·5Mg–O·3Cu alloy have been investigated. Results showed that dendrites were formed with porosity and cracks in the nugget. Grain boundary melting occurred in the heat affected zone and wide grain boundaries appeared. The alloy exhibited low hardness in the nugget centre. Tensile cracks propagated at the edge of the nugget and mixed rupture with dimples and intergranular fracture occurred. Fatigue fracture initiated at the edge of the nugget and propagated perpendicularly to the tensile axis. Transgranular fracture with striations was also observed.     

Thermal expansion anisotropy and site occupation of the pseudo-binary molybdenum vanadium silicide Mo5Si3–V5Si3

The coefficients of thermal expansion (CTEs) and atomic site occupation factors were measured for the pseudo-binary molybdenum–vanadium silicide Mo₅Si₃–V₅Si₃. The ratios of the CTEs in the crystallographic c and a directions range from 2.0 for Mo₅Si₃ to 1.2 for Mo₂V₃Si₃. The metal atoms can occupy chain sites (in the crystallographic c-direction), and non-chain sites. The relatively small V atoms prefer the chain sites in Mo₅Si₃, whereas the relatively large Mo atoms prefer the non-chain sites in V₅Si₃. These site-occupation characteristics reduce the thermal expansion in the c-direction and thereby the CTE anisotropy. Ab initio calculations for Mo₄VSi₃ suggest that, energetically, V prefers the chain sites, while the measurements show that V occupies also non-chain sites. Extrapolation of the experimental results assuming the site-occupation used in the calculations agrees with the theoretical result that the thermal expansion of Mo₄VSi₃ is isotropic.     

TEM Morphology and FCP Rate of Ti-5Al-2Mo-3Zr Alloy

The transmission electron microscopic morphology of the phases and fatigue crack propagation(FCP)rate ofTi-5Al-2Mo-3Zr alloy were investigated in this study.Mierostructiure of the alloy consists of α and β phases after furnace-andair-cooling,and interracial phase appears at the boundaries between these two phases.After water quenching,the microstructureconsists primary α and h.c.p.martensite α'which assumes acicular.There are a lot of twins within the α'plates.No retained βphase exists after quenching from any temperature.During aging,β particles precipitated along the boundaries and inside themartensite plates with Burgers orientation relationship.The fatigue crack propagation rate(low frequency)is not sensitive to themicrostructure,tensile strength and rolling direction.Analysis of the fractography shows that main cracks propagatedserpentinely and secondary cracks existed everywhere.In high stress intensity range,the resistance to FCP of the alloy is betterthan that of Ti-6Al-4V.     

Microstructure and transformation behavior of Ni50Ti45Ta5 shape memory alloy

1　INTRODUCTIONTheNiTishapememoryalloy (SMA )iscur rentlyatopicofnotableinterestinmedicine .Itpro videsauniqueopportunitytomakenovelsurgicalim plantsandinstrumentsforminimallyinvasive ,vascu larandorthopedicsurgery .Recently ,NiTiimplantshavebeendevelopedforcardiovascularandgastroin testinalsurgery[13] .ThehighnickelcontentofNiTi(5 4%bymass)cancauseproblemsinbiocompati bilitybecauseoftoxiceffectsofnickel[4 ] .Moreover ,thelowX rayvisibilityofNiTiSMAhaslimitedsomemedicalapplications …     

Crack Initiation and Propagation Evaluation for Sn–5Sb Solder Under Low-Cycle Fatigue

In this study, a crack initiation and propagation behavior of Sn–5Sb lead-free solder under low-cycle fatigue is discussed. Cyclic push–pull loading tests with a single-hole specimen have been conducted at 313 K to investigate the crack initiation and propagation behavior of Sn-5Sb solder which has a higher melting point temperature than that of Sn–Ag–Cu solders. A fatigue life ratio correlates with the crack length within a small scatter. Crack initiates at the early stage,and almost all the life period is crack propagation process independent of strain range and strain rate. The crack propagation rate depends on the strain range and the strain rate. The adaptation of J-integral value for Sn–5Sb solder is also discussed. J-integral value is a suitable parameter for crack propagation rate evaluation.     

Low-temperature performance and high-rate discharge capability of AB5-type non-stoichiometric hydrogen storage alloy

Low-temperature performance and high-rate discharge capability of AB5-type non-stoichiometric hydrogen storage are studied. X-ray diffraction（XRD）, pressure-composition-temperature（PCT） curves and electrochemical impedance spectroscopy（EIS） are applied to characterize the electrochemical properties of ABx （x=4.8, 4.9, 5.0, 5.1, 5.2） alloys. The results show that the non-stoichiometric alloys exhibit better electrochemical properties compared with that of the AB5 alloy.     

Thermal expansion anomaly and magnetic properties of Nd2AlFe11Mn5 compound

1 Introduction Materials with negative thermal expansion have many important applications as constituents of composite materials designed to reduce their overall thermal expansion. In 1991, ANDREEV and his co-workers investigated the properties of rare ea…     

Stability of CaNi5Hx stored at temperatures between 20 and 150°C

The stability of CaNi₅H_x stored at different temperatures was studied as a function of time. In general AB₅ metal hydrides are known to be metastable with a tendency to disproportionate at elevated temperatures. In the present study samples of CaNi₅ were stored in the hydrided state (as CaNi₅H_∼4.7) at temperatures between 20 and 150°C. After different periods of time, up to 120 days, the hydrogen absorption capacity was measured electrochemically. Significant capacity decays were observed at temperatures of 40°C and higher. The capacity decay with storage time tended to stop at a level of 147 mAh/g corresponding to 1.83 hydrogen atoms per calcium atom. X-ray diffraction revealed that the CaCu₅ structure was preserved after the degradation. A mathematical model for the decay is proposed.     

Effects of deformation on microstructures and properties of submicron crystalline Cu-5%Cr alloy

Warm extrusion of submicron crystalline Cu-5%Cr from 100 ℃ to 600 ℃ was investigated. The effects of different extrusion ratios and different extrusion temperatures on microstructures and properties of submicron crystalline Cu-5%Cr were studied. The microstructures of the extruded Cu-5%Cr were characterized by backscattered electron irnages（BSE） and transmission electron microscopy（TEM）. The mechanical properties of the extruded Cu-5%Cr were measured by means of microhardness and tension test. The results show that, the deformation, dynamic recovery and dynamic recrystallization of the extruded Cu-5%Cr are mainly produced in Cu matrix. The higher extrusion ratio leads to more uniform microstructure and finer Cu grains. When being extruded in the range of 100-600 ℃, dynamic recovery of Cu is the dominant process, and dynamic recrystallization of Cu occurred above 300 ℃ is far from end. The most part of microstructure of as-extruded Cu-5%Cr is subcrystaUines produced by dynamic recovery, only a few recrystallines exist, and the average size of these grains is not larger than 400 nm. With extrusion temperature rising, the tensile strength and microhardness of Cu-5%Cr decrease, and elongation increases gradually.     

Effect of particle size and agglomeration of TiO2 on synthesis and electrochemical properties of Li4Ti5O12

The effects of the initial condition of synthesis on electrochemical properties of Li4Ti5O12 were studied with the comparison among starting and final materials by SEM, XRD and electrochemical analysis methods. The influence of the solvents for mixing the starting material on the products was investigated. The results show that nano-sized Li4TisOlz powder obtained by nano-sized TiO2 with ethanolamine as solvent shows more excellent electrochemical performance. More than 95%, 91%, 85% and 71% of the nominal capacity is achieved respectively at 0.5C, 1C, 2C and 4C rate without excellent capacity fading after more than 30 cycles.     

Oxidation behavior of temary Fe- 15Cu-5Al and Fe-85Cu-5Al alloys in pure oxygen at 900℃

The oxidation of two two-phase ternary Fe-Cu-Al alloys containing about 5%（mole fraction） aluminium, one Fe-rich and one Cu-rich, has been studied at 900 ℃ in 1~105 Pa pure oxygen. The Fe-rich Fe-15Cu-5Al alloy presents two quasi-parabolic stages, with a large decrease of the parabolic rate constant after about 50min. The presence of 5% Al greatly reduces the oxidation rate of this alloy with respect to a binary Fe-Cu alloy of similar composition by forming an external protective Al203 layer, which is present near the scale/alloy interface. Due to the high stress-growth effect, this thin Al203 layer cannot completely prevent further oxidation of the alloy underneath. On the contrary, the Cu-rich Fe-85Cu-5Al alloy presents a single parabolic stage and forms a thick and porous external scale, coupled to the internal oxidation of Fe and Al. As a result, the oxidation of Cu-rich alloy at 900 ℃ is much faster than that of the Fe-rich alloy.