Valence electronic structure and cohesive property of a binary noble metal nitride

The valence electronic structure of a newly synthesized binary noble metal nitride PtN is obtained by utilizing an empirical electronic theory. The results reveal that the valence electron configuration of the nitride is: Pt 6s 0.143, 6p 1.286, 5d 3.0; N 2s 0.5694, 2p 2.4306. Such a configuration is different from that used to generate pseudopotential for the first principle calculations, and may explain why the calculated and experimental values of the bulk modulus of PtN cannot coincide. In addition, we also calculate the cohesive energy of this new phase based on the valence electronic structure, which is -674.75 kJ/mol.     

Preparation and characterization of SiO2 non-catalytic nucleation coating for the solidification of undercooled melt

SiO2 non-catalytic nucleation films were coated onto a ceramic substrate and the inner surface of a ceramic crucible by the Sol-Gel method. The surface morphology of the coatings was characterized with an atomic force microscope and a scanning electronic microscope. The non-catalytic effect of the coating on the heterogeneous nucleation of metal melts was tested through measuring the nucleation undercooling. Investigation results indicated that the prepared coating could act as a baffle-wall to prevent the metal melt from nucleating heterogeneously on the inner surface of the crystalline crucible. The tiny holes with a diameter below 2 μm and heaves on the coating surface have no evident effect on the undercooling of metal melts. For a poly-layer coating, the super-layer can cover the cracks in the sub-layers, which prevents the cracks in the coating from spreading in the direction vertical to the coating layers and thus eliminates the effect of cracks on the coating.     

Discussion of an Enrichment Mechanism of Precious Metals by Base Metals and Mattes in Pyrometallurgical Processes

The enrichment mechanisms of precious metals by base metals or their mattes in pyrometallurgical processes are discussed at the atomic level in this paper. The reasons brought forward for a trace amount of precious metals to be trapped into base metals or mattes are that the melted slag phases possess different chemical structures and properties from that of the melted base metal or matte phases. As for the melted slag phase, its formation is thought to depend on the covalent bonds and the ionic bonds between Si, O atoms and Ca2+, Mg2+, Fe2+ ions to tie up each other. Because the bridging electrons in the slag phase are all thought as the localized electrons, the precious metal atoms are not stable among them. However, as for the metal phase, its formation is thought depend on the metal bonds to bind up the metal atoms. Because the electrons in the metal phases can move freely among the atoms, the precious metal atoms that enter the metal phase can cause the system’s free energy to decrease. For the melted mattes phase,because it has high electrical conductivities (between 103～104 s·cm-1) at higher temperatures, and its temperature coefficients presents the negative values, its conductance mechanism belongs with the electronic conduction. The property of the mattes is in fact similar to that of the metal at their melted state, so the precious metal atoms will enter the matte phase instead of the slag phase in a mattesmelting process.     

Electronic structure of edge dislocation of core-doped Ti in Fe

The electronic structure of an edge dislocation doped Ti lying in the (001) plane with Burgers Vector along [100] direction in body-centered cubic iron is investigated using the first principles discrete variational method (DVM) based on the density-functional theory. The binding energy, impurity formation energy, interatomic energy, Mulliken orbital populations and charge density difference are presented in this paper. By calculating the binding energy of the clean dislocation system and the Ti-doped system, it is found that the binding energy of Ti-doped dislocation system is lower than that of the clean dislocation system, which implies that the Ti-doped dislocation system is more stable than the clean dislocation system. The calculated result of the impurity formation energy predicts the trapping effect of dislocation core for Ti, which shows that Ti atom prefers to occupy the place at the dislocation core. The calculated results of the interatomic energy and the difference charge density of dislocation doped Ti system indicate that the stronger bonding formed between the Ti impurity and its neighbor Fe atoms will affect the mechanical property of edge dislocation. Considering the influence of Ti on the electronic structure and the energies, we can predict that the trace Ti in transition metal Fe with dislocation defect can give a significant contribution to the solid solution hardening effects and will influence the mechanical property of materials.     

Research progress in interface modification and thermal conduction behavior of diamond/metal composites

Diamond/metal composites are widely used in aerospace and electronic packaging fields due to their outstanding high thermal conductivity and low expansion. However, the difference in chemical properties leads to interface incompatibility between diamond and metal,which has a considerable impact on the performance of the composites. To improve the interface compatibility between diamond and metal, it is necessary to modify the interface of composites. This paper reviews the experimental research ...     

A Research on the Joining of SiC Composite to 40 Cr Steel

SiC composites and 40 Cr Steels were joined with Ag-Cu-Ti solder in order to develop a new method of joining ceramics to metal. Effects of solder component and process parameters on the joining strength were investigated. The results show that some chemical reactions occur on the jointing interface between ceramics and metal. Higher joining strength is achieved when titanium is 0.2% (mass fraction) in the solder. The thickness of solder also affects the joining characteristics, and 0.2-0.3 mm thickness of solder is the most suitable.     

A Fair Off-Line Electronic Cash Scheme Based on Restrictive Partially Blind Signature

A fair off-line electronic cash scheme was presented based on a provable secure restrictive partially blind signature. The scheme is more efficient than those of previous works as the expiry date and denomination information are embedded in the electronic cash, which alleviates the storage pressure for the bank to check double spending, and the bank need not use different public keys for different coin values, shops and users need not carry a list of bank‘s public keys to verify in their electronic wallet. The modular exponentiations are reduced for both the user and the bank by letting the trustee publish the public values with different structure as those of previous electronic cash schemes. The scheme security is based on the random oracle model and the decision Diffie-Hellman assumption. The scheme can be easily extended to multi-trustees and multi-banks using threshold cryptography.     

A protocol for fair electronic purchase based on concurrent signatures

E-commerce protocols for the electronic purchase of goods are difficult to design and implement due to their complexity and high security demands. Fairness of such protocols in literature highly depends on an additional TTP（trusted third party）. However, it is difficult to find such a TTP in some situations. In addition, fairness for customers has been neither fully considered nor well satisfied in existing electronic purchasing protocols. In this paper, a new protocol FEP （fair electronic purchase） without a special TTP but an online bank is presented based on a concurrent digital signature scheme. The FEP protocol guarantees fair electronic purchase of goods via electronic payment between consumers, merchants and their online banks. The protocol is practical and the analysis based on the game logics shows that it achieves the properties of viability, fairness, and timeliness.     

Preliminary study on theory and experiment of photo-mechanics manufacturing based on laser thermal stress

Mechanics effect of laser thermal stress is a new manufacturing technology, which uses thermal stress by high power laser acted on the surface of metal material to produce stress field. The technologies such as sheet metal formation by laser thermal stress, measurement by laser scratching and measurement by XRD （ X-ray diffraction ） are formed based on mechanics effects of laser thermal stress. The mechanisms of sheet metal formation by laser thermal stress, measurement by laser scratching and measurement by XRD are analyzed, and the theory of photo-mechanics manufacturing and detecting technologies based on laser thermal stress is originally put forward, whose experiment is primitively researched, and the manufacturing theory by mechanics effects of laser thermal stress is established.     

Study on the passive film formed on 2205 stainless steel in acetic acid by AAS and XPS

The properties of the passive film formed on 2205 stainless steel in acetic acid at high temperature that contained chloride ions were studied by atomic absorption spectrometry (AAS), X-ray photoelectron spectroscopy (XPS), and electrochemical polarization measurements. AAS results show that molybdenum is enriched on the surface as the passive film is dissolved. This enrichment decreases the corrosion resistance because it hinders chloride adsorption and Fe ion dissolution, and acts as a local pH buffer because it consumes protons. The dissolution ratio of Fe/Cr is approximately 10 during the active dissolution of the passive film. XPS results indicate that when the potential is in the passivation region, Cr comprises about 50% of the metal cations in the near-surface region of the passive film and is the main metal constituent in this region. When the polarization potential is much greater than the transpassivation potential, the Mo content accounts for approximately 45% of the metal cations in the nearurface region; Fe and Ni have no obvious influence on the formation, dissolution, or puncture of the passive film.     

Fair Electronic Payment Scheme Based on DSA

We present a multi-signature scheme based on DSA and describes a fair electronic payment scheme based on improved DSA signatures. The scheme makes both sides in equal positions during the course of electronic transaction, A Trusted Third Party (TTP) is involved in the scheme to guarantee the fairness of the scheme for both sides. However, only during the course of registration and dispute resolution will TTP be needed. TTP is not needed during the normal payment stage.     

Study of Compound Polishing Process on SnSb Alloy Moulds

The characteristic of metallographic structure of the SnSb alloy moulds is that hard particles are distributed on the soft metal matrix. Great difference of the hard particles and the soft metal matrix‘hardness makes moulds‘polishing become difficult. When a rigid grindstone is used to polish the surface of the SnSb alloy mould, the hard abrasives fall off and are embed in the soft matrix of SnSb alloy and while the process, the grinding chips are able to block the gap on the grindstone surface and enable t...     

First-principles study of the effects of Si doping on geometric and electronic structure of closed carbon nanotube

The effects of Si doping on geometric and electronic structure of closed carbon nanotube （CNT） are studied by, a first-principles method, DMol. It is found that the local density of states at the Fermi level （Er） increases due to the Si-doping and the non-occupied states above the Er go down toward the lower energy range under an external electronic field. In addition, due to the doping of Si, a sub-tip on the CNT cap is formed, which consisted of the Si atom and its neighbor C atoms. From these results it is concluded that Si-doping is beneficial to the CNT field emission properties.     

Relaxation mechanism analysis of synthetic fused quartz glass investigated by electrical impedance spectra

The synthetic fused quartz glasses with bare metal impurities have been analyzed by temperature- dependent electrical impedance spectroscopy. The complex electric impedance and the overlapping of the normalized dielectric modulus imply the single mechanism of dielectric and conduction relaxation in the fused quartz glass. Besides, the dependence of conductivity on temperature may attribute to the predominant electric relaxation to the delocalized or long range electronic hopping between the nonbridged dangling oxygen.     

A quantum mode theory of the micromaser

Failure of the steady solution of the master equation was analysed. It was found that the state of sustained oscillation exists only when the ratio of photon decay rate γ to injection rate r is satisfied. Based on this understanding, a quantum mode micromaser theory was developed. The threshold ν th and photon distribution for π and 2π mode were calculated. The instability of quantum mode was analyzed as well.     

Electronic properties and stabilities of methoxy-substituted Lindqvist polyoxometalates [Nb2W4019CH3]3- by DFT

The electronic properties and stabilities of five [Nb2W4O18OCH3]3-isomers have been investigated using a density functional theory method.The results show that the isomer with the methoxy group occupying a bridging position between two tungsten atoms(two tungsten atoms in the plane that contains two niobium atoms) in the [Nb2W4O18OCH3]3-framework is the most stable isomer in acetonitrile.The stability of the one-electron-reduced isomers changes little.The most stable one-electron-reduced isomer has the methoxy group occupying a bridging position between niobium atoms in the [Nb2W4O18OCH3]4-framework.The M-Ob(M = Nb,W;b denotes bridging) bond lengths in anions in which the metal atoms are connected by a methoxy group are longer than those in [Nb2W4O19]4-.The highest occupied molecular orbitals(HOMO) in [Nb2W4O19]4-mainly delocalize over the bridging oxygen atoms of two niobium atoms and two tungsten atoms located in the equatorial plane,and the bridging oxygen atoms on the axial surface.The lowest unoccupied molecular orbitals(LUMO) of [Nb2W4O19]4-are mainly concentrated on the tungsten atoms and antibonding oxygen atoms.Methoxy substitution modifies the electronic properties of the [Nb2W4O18OCH3]3-isomers.The HOMOs in the five isomers formally delocalize over the bridging oxygen atoms,which are distant from the surface containing the methoxy group and four metal atoms.The LUMOs delocalize over the d-shells of the four metal atoms that are close to the methoxy group,and the p-orbitals of oxygen.One-electron reduction occurred at the tungsten atoms,not the niobium atoms.     

Electronic transport properties of capped-carbon-nanotube-based molecular junctions with multiple N and B dopants

By applying non-equilibrium Green’s function in combination with density functional theory,we investigated the electronic transport properties of capped-carbon-nanotube-based molecular junctions with multiple N and B dopants.The results show that the electronic transport properties are strongly dependent on the numbers and positions of N and B dopants.Best rectifying behavior is observed in the case with one N and one B dopants,and it is deteriorated strongly with the increasing dopants.The rectifying direction is even reversed with the change of doping positions.Moreover,obvious negative differential resistance behavior at very low bias is observed in some doping cases.     

Charging for the waste dumping of open-pit metal mines

Based on the externality theory and the environmental value theory, the hypothesis of charging for waste dumping of open-pit metal mines was put forth. The charging methods were designed according to the characteristics of waste dumping of openpit metal mines, including charging based on the dumping amount of the total waste, multi-charging factors, exceeding standard punishment charging, and so on. The main charging parameter is based on the dumping area rather than the total amount of waste dumping.The charging model of waste dumping of open-pit mines was formulated, and the charging rate was divided into two parts, i.e., the standard charging rate and the differential charging rate. The standard charging rate was derived using the equilibrium dynamic model,whereas the differential one was obtained by establishing the fuzzy synthesized evaluation model.     

First-principles investigation of the alloying effect of Ta and W on γ -TiAl

The alloying effect of the refractory elements Ta and W on the electronic structure of y-T\A\ is investigated by using the first-principles discrete variational method within the framework of density functional theory. The impurity formation energy result indicates that Ta and W can stay steadily in the TiAl system by way of substitution. The Mulliken population, density of states and charge density difference results show that Ta and W both give rise to the strong interaction between themselves and the neighboring host atoms. The alloying effect of the two elements onγ-TiAl is the same.     

Field emission study of CNTs on metal tips

The field emission characteristics of multiwalled carbon nanotubes grown on metal tips are studied at various temperatures. It is found that emission current at a given applied electric field increased with the temperature, and the stability of the current did not change. The dependence upon temperature varies quite differently with the metal substrates. This may result from the asymmetry of the CNTs and the interface effect between CNT and underlay.