Structure and electronic properties of the Watson–Crick base pairs: Role of hydrogen bonding

The hydrogen bonding patterns in the adenine–thymine (A–T) and guanine–cytosine (G–C) base pairs for B-DNA has been studied using the density functional theory. The H-bond for the crystal geometry is found to differ considerably from the geometry optimized structures for the free base pairs with larger deviation for the G–C pair compared to the A–T pair. Furthermore, the H-bonding patterns are found to be highly non-local and co-operative. For the N···HN bond in the G–C pair, the proton hops in between two symmetric double-well potentials localized on the donor and the acceptor, due to cancellation of the local polarizations of the top and down NH···O and O···HN bonds, respectively. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) gap (HOMO–LUMO gap) for the free bases decreases with increase in the strength of the H-bonds in between the base pairs with larger decrease for the G–C pair. The adiabatic electron affinity (AEA) for the free bases which are found to be all negative become positive on the formation of the H-bonds and more so for the G–C pair.     

Physicochemical properties of 1,3-dimethyl-2-imidazolinone−ZnCl2 solvated ionic liquid and its application in zinc electrodeposition

Zinc chloride (ZnCl₂) was dissolved in the 1,3-dimethyl-2-imidazolinone (DMI) solvent, and the metallic zinc coatings were obtained by electrodeposition in room-temperature ambient air. The conductivity (σ), viscosity (η), and density (ρ) of the DMI?ZnCl₂ solvated ionic liquid at various temperatures (T) were measured and fitted. Furthermore, cyclic voltammetry was used to study the electrochemical behavior of Zn(II) in the DMI?ZnCl₂ solvated ionic liquid, indicating that the reduction of Zn(II) on the tungsten electrode was a one-step two-electron transfer irreversible process. XRD and SEM?EDS analysis of the cathode product confirmed that the deposited coating was metallic zinc. Finally, the effects of deposition potential, temperature and duration on the morphology of zinc coatings were investigated. The results showed that a dense and uniform zinc coating was obtained by potentiostatic electro- deposition at ?2 V (vs Pt) and 353 K for 1 h.     

Synthesis and characterization of polyaniline–maleic acid salt

Polyaniline–maleic acid (PANI–MAc) salts have been prepared at various maleic acid concentrations. The salts are characterized by using infrared (IR), UV/VIS Spectroscopy, thermogravimetric analysis and conductivity measurements. Blends of PANI–MAc were made with styrene–butyl acrylate (ST–BuA) copolymer and percolation threshold determined.     

Solubility and rheological characterization of polyaniline base in N-methyl-2-pyrrolidinone and N,N′-dimethylpropylene urea

The thermodynamic ‘goodness’ of N-methyl-2-pyrrolidinone (NMP) and N,N′-dimethylpropylene urea (DMPU) as solvents for polyaniline (PANI) (emeraldine base) were compared by studying the dilute solution viscometry of solutions of PANI in NMP and DMPU. The intrinsic viscosity of PANI polymer in NMP was found to be 0.71 dl g⁻¹, whereas the same polymer in DMPU had an intrinsic viscosity of 0.77 dl g⁻¹, which indicates that DMPU is a ‘better’ solvent for PANI. The rheology and rheological stability of solutions of PANI in NMP and DMPU were studied by cone and plate rheometry. A 10% PANI solution in NMP gelled within 60 min, whereas a 17.5% solution in DMPU did not show any change in its viscosity for as long as 400 min. Solutions of PANI (10–17.5%) in DMPU displayed prominent shear thinning behaviour at lower shear rates (below 3 s⁻¹ and Newtonian behaviour at higher shear rates (3–15 s⁻¹). A solution of 10% PANI in NMP showed a similar prominent shear thinning followed by a gradual decrease in viscosity with an increase in shear rates, presumably due to breaking of the ‘weak’ thixotropic gel.     

Solder joint geometry of tin-lead alloy and its application in electronic packaging

1lNTR0DUCTIONInmaterialsscienceandengineering,manyphenomenaandpropertiesdepend0ntheshapeofinterfacesandsurfaces,stabilityandassociat-edpotentials.Inthefields0felectronicpackag-ingandsurfacemounttechnology,thehighden-sityandhighreliabilityarethecurrentneedsandthefuturetrends.Thereliabilityandthemanu-facturingprocessoftin-lead(SnPb)basedso1derjointaretheessentialproblemsofelectronicpackagingindustry.Previous....ar.h..[1'2]haveprovedthatthesolderjointgeometryplaysanimportantroleinsolderjoint…     

Macro—and microstructural changes in hydrogenated TiMn2 and Ta

Binary TiMn2 alloys with various compositions were arc melted in an Ar atmosphere.These alloys consist of TiMn2 and a small amount of TiMn depending on alloy composition.Annealed Ti-59.4%Mn exhibits the greatest capacity for hydrogen absorption and the smallest degradation of capacity during repeated hydrogen absorption and desorption.No apparent macro-and microstructural chanes are observed in Ti-59.4%Mn by repeated hydrogenation of 30cycles.At Mn content higher than 59.4%Mn,the formation of nano-sized Ti-hydride and the lattice expansion due to retained interstitial hydrogen were confirmed in repeatedly hydrogenated alloys.Pulverized powders were refined in all the alloys with increasing the number of repeated hydrogenation cycles.Many onion-like cracks are introduced in annealed pure Ta with 100℃m equi-axed grains by holding at 1473K followed by furnace cooling to room temperature in a hydrogen atmosphere,but no crack is observed after holding at 1473K in a hydrogen atmosphere followed by furnace cooling in an Ar atmosphere.It is concluded that the surface activation is attained in a hydrogen atmosphere at 1473K and multiple cracking occurs by absorbing a large amount of hydrogen at lower temperature.Volume expansion and dislocations generated by hydrogenation and hydride formation are responsible for multiple cracking.Hydrogen-induced multiple cracking in Ta occurs in the following sequence:hydrogen absorption,lattice expansion,hydride formation,and crack nucleation and propagation.Powder fabrication of Ta by hydrogenation is discussed in comparison with the hydrogen pulverization of intermetallic alloys.     

Modelling the thermal oxidation of ternary alloys—compositional changes in the alloy and the development of oxide phases

A coupled thermodynamic–kinetic oxidation model is presented that describes the thermal oxidation of a single-phase ternary alloy. For given oxide-layer growth kinetics, the model computes composition–depth profiles in the alloy, as well as the amount of each oxide phase developed as a function of oxidation time, including the formation of multiple oxide phases during the initial stage of fast oxidation. Application of the model to the thermal oxidation of a γ-Ni–27Cr–9Al (at.%) alloy at 1373 K and a partial oxygen pressure (p_O2) of 2×10⁴ Pa showed that the phase constitution of the developing oxide layer is predominantly governed by the growth rate and duration of the initial oxidation stage, whereas the eventual, steady-state interface composition of the alloy is mainly determined by the parabolic oxide-layer growth rate.     

Dislocation configurations and stress-corrosion properties of alloys in the nickel—chromium—iron system

Abstract

Stress-corrosion tests have been performed in sodium chloride at 300° on commercially produced and laboratory-made nickel alloysand austenitic steels. It has been found that resistance to transgranular stress corrosion cracking depends upon the (Ni + Cr) content. Commercial high-Ni alloys are resistant, as are relatively pure Ni–Cr–Fe alloys with (Ni + Cr) ≥ 50% wt. The resistance of alloys with approximately 20% Cr and 20—40% Ni is markedly influenced by other alloying elements, for example, silicon and molybdenum.

Electron microscope studies indicate that resistance to cracking can be approximately correlated with the extent to which dislocation ‘tangling’ occurs at a particular deformation. Planar dislocation arrays appear to be a necessary, though not sufficient,condition for susceptibility. It is thought that the observed dislocation arrangements can be understood without recourse to hypotheses of ordering in these alloys. The influence of some alloying elements, e.g. chromium and silicon, cannot be interpreted simply in terms of their influenceon dislocation arrangements. The favourable effectof these elementson resistance to stress-corrosion cracking is probably associated withtheir ability to increase the protective properties of surface oxide films and thus to inhibit the crack initiation process.     

Preparation of cobalt-modified magnetite and its magnetic properties

Magnetite was modified by reaction with alkaline solution containing Co^2 and Fe^2 to obtain a cobalt ferrite layer on the surface of particles. The influences of modification conditions on the properties were investigated. The as-prepared particles were characterized by X-ray diffraction(XRD) and transmission electron microscope(TEM). The results show that pH value influences the particles composition directly, the desirable CoFe2O4 is obtained as pH value is 12. The coercivity of particles increases with the increase of cobalt content, and the cobalt efficiency reaches a maximum value at cobalt content of 2.71% (mass fraction). With cobalt modification, the magnetite particles have the similar lattice constant and structure to that without cobalt modification, and the squareness ratio is almost 0.5. The increase of the coercivity is attributed to the uniaxial magnetic anisotropy and magnetocrystalline anisotropy of cobalt-ferrite itself.     

Role of the structural state of a copper–beryllium alloy in the formation of its tribotechnical properties

The influence of the structural state of a copper–beryllium alloy on its resistance to friction fracture under adhesion interaction and abrasive wear has been investigated. It has been shown that the elastic interphase deformations that cause the tension of the crystal lattice of the particles of precipitated phase brings about a decrease in the wear resistance of the alloy at a retained high hardness. The relaxation of interphase deformations during the aging process leads to a significant increase in the wear resistance of the alloy, despite the reduction its hardness.     

Effect of Y on structure and properties of copper and its alloy

The possibility of substituting 72.5Cu-22.7Zn-3.4Al brass for phosphorus bronze in some case that is now extensively used for elastic component, and purifying the scrap copper for recycling metal was investigated. By adding a little amount of rare earth Y into scrap copper and 72.5Cu-22.7Zn-3.4Al brass to research their structure and characteristics, especially the electric conductivity for scrap copper and HV for the brass were researched. The results show that the tensile strength, elongation and electric conductivity （IACS） of 0.38 mm strip of scrap copper with 0.04% Y, are 213.8 MPa, 23% and 98.5% that suit for the elastic components. The tensile strength, elongation and HV of 0.25mm strip of the brass with 0.03% Y are 665.1MPa, 2.86% and 226 that satisfy the usage requirement for the elastic components. Meanwhile, the cost is cheaper than phosphorous bronze because of implying 22.7% zinc in the brass, which has the actual application value.     

ZrNi–H2: microstructural analysis of the thermodynamically controlled hydride phase growth,and electronic properties

The ZrNi–H₂ phase diagram indicates the presence of two stable hydrides: a triclinic monohydride ZrNiH and an orthorhombic trihydride ZrNiH₃ [1]. In this paper, we present the results of some thermodynamic, microstructural and electronic properties of the ZrNi–H₂ system. A strict control of the thermodynamic variables (P, T) during the hydride phase growth allowed us to prepare two samples of overall composition ZrNiH_0.70 and ZrNiH_2.5. In a first step, the microstructure evolutions induced by hydrogen absorption are investigated during the activation process. The intermetallic and hydrided compounds are studied by energy dispersive X-ray spectroscopy (EDXS) and X-ray diffraction (XRD) methods. The nature of defects generated in ZrNi and its hydrides compounds are observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Ab-initio electronic structure calculations have been performed. They clearly show the importance of chemical effects besides geometrical factors in explaining the preferential site occupancy of hydrogen atoms in the ZrNiH phase.     

Synthesis of Ti2AlC by hot pressing and its mechanical and electrical properties

Ti2AlC bulk material was synthesized by hot pressing of mixture powders of TiC, Ti, Al and active carbon. The phase compositions of resultant product at different temperature were detected by X-ray diffractometer. The microstructures of the samples were observed by SEM. Finally, the mechanical properties and thermal properties of the sample at 1 400 ℃ were measured. The results show that high purity Ti2AlC material with little Ti3AlC2 can be synthesized by hot pressing 0.5TIC/1.5Ti/1.0A1/0.5C at 1 400 ℃. Ti2AlC exhibits high mechanical properties and metallic electrical properties. Its fractm＇e toughness is 7.0 MPa·m^1/2, its flexural strength is 384 MPa at room temperature, and its electrical conductivity is 2.56 × 10^6 Ω^-1·m^-1 at room temperature.     

Density functional study for structure and electronic properties of FeS_2(100)

1　INTRODUCTIONThereactivityoftheFeS2 (pyrite)surfaceisofparticularimportantintheengineeringapplications ,includingsulfidemineralsflotation[1] ,bioleachingoflow gradechalcopyrite containingore[2 ] ,coal pro cessing ,hydrometallurgy ,environmentalengineer ing ,geochemistry ,andphotovoltaiccell,etc[3] .Es pecially ,anunderstandingofhow pyritesurfacesin teractwithflotationreagentmoleculeswillaidinthedesignofmoreeffectiveflotationsuppressants ,whichwouldeffectivelyseparatethedesirableoresfrom…     

Mechano-activated surface modification of calcium carbonate in wet stirred mill and its properties

Surface modification of calcium carbonate particles using sodium stearate（SDS） as a modification agent incorporated with the simultaneous wet ultra-fine grinding in the laboratory stirred mill was investigated. The physical properties and application properties of modified calcium carbonate were measured and evaluated. The action mechanism between SDS and calcium carbonate in the modification was studied by infi＇ared spectrometry（IR） and X-ray photoelectron energy spectroscopy（XPS）. The results indicate that the crushing mechanic force intensity can obviously influence the modification effect of calcium carbonate because of mechano-chemical effect. The hydrophilic surface of calcium carbonate is turned into hydrophobic after modification. The properties of polyethylene（PE） filled by modified calcium carbonate powder is markedly improved. And the adsorption of SDS could occur by chemical reaction with calcium carbonate surface.     

Microstructure of sepiolite and its adsorbing properties to dodecanol

The acid treatment process, testing methods, microstrcture of sepiolite mineral materials and their adsorbing properties to dodecanol were studied respectively. The results show that by acid treatment to raw sepiolite thinner fibre clusters and single fibres turn up, the pore volume and the number of micropore and mesopore in sepiolite all increase, and adsorbing properties of modified sepiolite to dodecanol are improved significantly. In the combined materials of dodecanol and sepiolite prepared under the best condition, the proportion ofdodecanol is 67.96%, and then it is much higher than the result calculated from traditional BET method.     

Application of nanotechnology in a silver／graphite contact material and optimization of its physical and mechanical properties

By applying nanotechnology, a new type of silver/graphite (AgC) electrical contact was fabricated and charac-terized. The AgC coating powders were obtained through high-energy ball milling and reducer liquid spraying-coating method. The as-prepared powders were examined by transmission electron microscope (TEM), scanning electron micro-scope (SEM), and X-my diffraction (XRD). The results show that the thickness of graphite flakes milled for 10 h is about 50-60 nm and the AgC coating powders exhibit flocculent structure with quite free and homogeneous intemal micropores.XRD implies that the average crystalline size of silver in coating powders is about 50 rim. The mechanical and physical properties of this newly developed AgC contact made from the above-mentioned nanocrystalline powders by traditional powder metallurgy technique were measured. Compared with its counterparts made from other techniques, the properties of this new AgC contact have been optimized. High surface energy and high-energy interfaces of the nanocrystalline AgC coating powders provide powerful driving force for sintering densification. Moreover, the flocculent structure of the pow-ders is also an important factor to acquire fine density ratio.     

Free ferrite in pearlitic ductile iron—morphology and its influence on mechanical properties

The present research focuses on the study of the precipitation of free ferrite in ductile iron during cooling through the intercritical temperature range. The main objectives are to recognize the morphology of the free ferrite precipitated in pearlitic ductile iron alloyed with Cu and Mn, and to evaluate the mechanical properties resulting from different microstructures. The microstructures investigated were generated by normalising heat treatments from regular and low austenitising temperatures. The results indicate that different free ferrite morphologies are produced depending on the thermal cycles carried out. As-cast samples present bull's eye morphology, while austenite grain boundary precipitation dominates in recrystallised structures. Low austenitising temperature normalising causes, in the alloys studied, the formation of a fine network of free ferrite precipitated within the pearlitic matrix at the recrystallised austenite grain boundaries. Low austenitising temperature normalising markedly improved the mechanical properties of ductile iron, surpassing the elongation of conventional normalising, and retaining similar levels of hardness and strength. This treatment has been found useful to counterbalance low ductility induced by intercellular carbide precipitation.     

Charge transfer driven surface segregation of gold atoms in 13-atom Au–Ag nanoalloys and its relevance to their structural,optical and electronic properties

The structural, optical and electronic properties of 13-atom Ag–Au nanoalloys are determined by a combination of global optimization using semi-empirical potentials and density functional theory calculations. A family of Au surface-segregated structures are found for core–shell Ag_nAu_13−n (n = 1, 2, 3, 5, 7, 8, 9, 12) and hollow Ag_nAu_13−n (n = 4, 6, 10, 11) clusters, whose stability is enhanced by directional charge transfer. The atomic ordering in core–shell structures is related to the electric dipole moment and odd-numbered surface Au-atom clusters have high moments. Their ferroelectric and ferromagnetic properties provide a potential approach for tailoring their surface plasmonic modes.     

New modelling of the B2 phase and its associated martensitic transformation in the Ti–Ni system

A symmetric two-sublattice model (Ni, Ti, Va)_0.5(Ni, Ti, Va)_0.5 is applied to describe the intermediate B2 compound in order to cope with the order–disorder transition in the Ti–Ni system. Using this model, the ordered B2 and the disordered Ti-rich b.c.c. are described by a single Gibbs free energy function. The B2 phase is the parent phase of the martensitic transformation in the TiNi shape memory alloys (SMAs), and its thermodynamic properties are then reassessed with emphasis on its composition range that is critical for SMAs. The low temperature B19′ phase is also evaluated on the basis of the selected experimental data from the martensitic transformation. Properties related to the transformation are studied in comparison with experimental data. The magnetic contribution is examined for the martensitic transformation. All calculations are in satisfactory agreement with experimental phenomena.