Effects of electric pulse modification on liquid structure of Al-5%Cu alloy

The electric pulse modification （EP, EPM） of liquid metal is a novel method for grain refinement. The structure of EP-modified Al-5%Cu melt was characterized by high-temperature X-ray diffractometry. The results show that the Cu-containing Al clusters remarkably increase in the EP-modified melt, furthermore, these clusters in that case tend to contract due to the decrease of relevant atomic radius and the co-ordination number. This kind of liquid-phase structure leads to a more homogeneous Cu-rich phase distribution in the final solidification structure. Differential scanning calorimetry （DSC） tests indicate that the solidification super-cooling degree of the EP-modified liquid phase is 2.36 times that of the unmodified. These facts suggest that the atom cluster changes in EP-modified Al-5%Cu melt would disagree with that by EPM model previously proposed in liquid pure metal.

Structure of Liquid Aluminum and Hydrogen Absorption

The hydrogen content in aluminum melts at different temperature was detected. The structure in aluminum melts was investigated by molecular dynamics simulation. The first peak position of pair correlation function, atomic coordination number and viscosity of aluminum melts were calculated and they changed abnormally in the same temperature range. The mechanism of hydrogen absorption has been discussed. From molecular dynamics calculations, the interdependence between melt structural properties and hydrogen absorption were obtained.

Effect of electric field on the activity and quenching structure of liquid Cu-Al alloys

The activity coefficient of Al in molten Cu decreases with the increasing of electric current applied to the liquid alloy of Cu-0.2wt%Al. To investigate the mechanism, the quenching experimental results of the liquid Al-Cu alloy show that there is a re- markable change in structure, in which the solute congregates along the current direction especially for DC current. The mechanism of the activity coefficient change of Al in molten Cu-0.2wt%Al alloy treated by electrical field was discussed. Further, the results also provide an evidence for the short-range-ordered liquid metal.

Liquid−liquid structure transition in metallic melt and its impact on solidification:A review

Understanding the nature of liquid structures and properties has always been a hot field in condensed matter physics and metallic materials science.The liquid is not homogeneous and the local structures inside change discontinuously with temperature,pressure,etc.The liquid will experience liquid−liquid structure transition under a certain condition.Liquid−liquid structure transition widely exists in many metals and alloys and plays an important role in the final microstructure and the properties of the solid alloys.This work provides a comprehensive review on this unique structure transition in the metallic liquid together with the recent progress of its impact on the following microstructure and properties after solidification.These effects are discussed by integrating them into different experimental results and theoretical considerations.The application of liquid−liquid structure transition as a strategy to tailor the properties of metals and alloys is proven to be practical and efficient.

Molecular Dynamics Simulations of Liquid Phosphorus at High Temperature and Pressure

By performing ab initio molecular dynamics simulations, we have investigated the microstructure, dynamical and electronic properties of liquid phosphorus （P） under high temperature and pressure. In our simulations, the calculated coordination number （CN） changes discontinuously with density, and seems to increase rapidly after liquid P is compressed to 2.5 g/cm3. Under compression, liquid P shows the first-order liquid-liquid phase transition from the molecular liquid composed of the tetrahedral P4 molecules to complex polymeric form with three-dimensional network structure, accompanied by the nonmetal to metal transition of the electronic structure. The order parameters Q6 and Q4 are sensitive to the microstructural change of liquid P. By calculating diffusion coefficients, we show the dynamical anomaly of liquid P by compression. At lower temperatures, a maximum exists at the diffusion coefficients as a function of density; at higher temperatures, the anomalous behavior is weakened. The excess entropy shows the same phenomena as the diffusion coefficients. By analysis of the angle distribution functions and angular limited triplet correlation functions, we can clearly find that the Peierls distortion in polymeric form of liquid P is reduced by further compression.

Metastable Phase Separation and Concomitant Solute Redistribution of Liquid Fe-Cu-Sn Ternary Alloy

Liquid Fe-Cu-Sn ternary alloys with lower Sn contents are usually assumed to display a peritectic-type solidification process under equilibrium condition. Here we show that liquid Fe47.5Cu47.5Sn5 ternary alloy exhibits a metastable immiscibility gap in the undercooling range of 51-329 K （0.19TL）. Macroscopic phase separation occurs once undercooling exceeds 196 K and causes the formation of a floating Fe-rich zone and a descending Cu-rich zone. Solute redistribution induces the depletion of Sn concentration in the Fe-rich zone and its enrichment in the Cu-rich zone. The primary Fe phase grows dendritically and its growth velocity increases with undercooling until the appearance of notable macrosegregation, but will decrease if undercooling further increases beyond 236 K. The microsegregation degrees of both solutes in Fe and Cu phases vary only slightly with undercooling.

Influence of Liquid Structure on Solid Transformation of CuAINi Shape Memory Alloy

Molten Cu-13AI and Cu-13AI-4Ni (mass fraction) alloys have been investigated using X-ray diffraction method. A distinct pre-peak has been found in the structure factors. The pre-peak increases its intensity with decreasing temperature and addition of Ni. The structural unit size corresponding to the pre-peak equals to magnitude of (111) planar distance of phase. The appearance of a pre-peak is due to existence of clusters with -phase-like structure in melt. Quantity and size of clusters increase with decreasing temperature but their structural unit size remains constant. Cu-13AI-4Ni shape memory alloy ribbons can be fabricated by rapid solidification technique. Order degree of martensite and temperature of the reverse martensitic transformation increase with decreasing liquid quenching temperature. phase particles develop from incorporating and growing of the clusters during solidification, thus result in the correlation between liquid structure and solid transformation.

Origin of the pre-peak in the structure factor of liquid Fe-4.30C-0.21Ce alloy

The liquid structure of Fe-4.30C and Fe-4.30C-0.21Ce alloys was studied by high temperature X-ray diffractometer. The results show that for Fe-C alloy the nearest neighbor distance of the eutectic alloy is 0.259-0.260 nm at the temperature range of 1200-1400℃, which increases to 0.269-0.271 nm with the addition of 0.21% (mass fraction) Ce in the Fe-C alloy at the same temperature range. There is a pre-peak at Q = 15.5 nm-1 on the original intensity curve and structure factor S(Q) of the liquid Fe-4.30C-0.21Ce alloy, which was caused by the Ce atoms in the C-Ce clusters. Combined with the shared face, the tetragonal structure can meet the requirement for the distance of Ce-Ce atoms. It also shows that the cluster size in the liquid Fe-4.30C-0.21Ce alloy increases with the decreasing temperature.

STRUCTURE OF THERMOTROPIC LIQUID CRYSTALLINE VANILLIC ACID/P-HYDROXYBENZOIC ACID/ETHYLENE TEREPHTHALATE VHE TERPOLYESTERS

Thermotropic liquid crystalline VHE terpolyesters made from vanillic acid (V),p-hydroxybenzoic acid (H) and poly(ethylene terephthalate) (E) were studied by 400 MHz NMR spectra, wide angle X-ray diffraction,scanning electron and polarizing microscopes.It was found that the VHE terpolyesters had random sequence distribution.The VHE terpolyester films exhibited highly oriented fibrillar structure.

Liquid structure of pure iron by X-ray diffraction

The liquid structure of pure iron at 1540, 1560 and 1580 deg C was studied byX-ray diffraction. The results show that near the melting point there is a medium-range orderstructure that fades away with the increasing temperature. The average nearest distance of atoms isalmost independent of the melts temperature, but the average coordination number, the atom clustersize and the atom number in an atom cluster all decrease with the increasing temperature of themelt. Near the melting point there are a lot of atom clusters in the pure iron melt. The atomcluster of pure iron has the body-centered cubic lattices, which are kept from the solid state. Andthe body-centered cubic lattices connect into network by occupying a same edge. The atoms in thesurrounding of the atom clusters are arranged disorderly.

A New Simulation of Track Structure of Low-Energy Electrons in Liquid Water:Considering the Condensed-Phase Effect on Electron Elastic Scattering

A new Monte Carlo simulation of the track structure of low-energy electrons （〈10keV） in liquid water is presented. The feature of the simulation is taken into consideration of the condensed-phase effect of liquid water on electron elastic scattering with the use of the Champion model, while the dielectric response formalism incorporating the optical-data model developed by Emfietzoglou et al. is applied for calculating the electron inelastic scattering. The spatial distributions of energy deposition and inelastic scattering events of low-energy electrons with different primary energies in liquid water are calculated and compared with other theoretical evaluations. The present work shows that the condensed-phase effect of liquid water on electron elastic scattering may be of the influence on the fraction of absorbed energy and distribution of inelastic scattering events at lower primary energies, which also indicate potential effects on the DNA damage induced by low-energy electrons.

Structural deformation of nitro group of nitromethane molecule in liquid phase in an intense femtosecond laser field

The structural deformation of NO2 group induced by an intense femtosecond laser field of liquid nitromethane（NM）molecule is detected by time-and frequency-resolved coherent anti-Stokes Raman spectroscopy（CARS） technique with the intense pump laser. Here, we present the mechanism of molecular alignment and deformation. The CARS spectra and its FFT spectra of liquid NM show that the NO2 torsional mode couples with the CN symmetric stretching mode and that the NO2 group undergoes ultrafast structural deformation with a relaxation time of 195 fs. The frequency of the NO2 torsional mode in liquid NM（50.8±0.3 cm^-1） at room temperature is found. Our results prove the structural deformation of two groups in liquid NM molecule occur simultaneously in the intense laser field.

Detailing the Structure of Liquid THF Based on an EPSR Study

The structure of pure liquid tetrahydrofuran (THF) has been investigated via Monte Carlo simulations in the wake of a previous Empirical Potential Structure Refinement (EPSR) study on that liquid (Bowron, D.T.;Finney, J.L.;Soper, A.K. (2006) J. Am. Chem. Soc., 128, 5119). The molecules are allatoms rigid structures and the intermolecular potential used is described for the classical 6-12 Lennard-Jones plus Coulomb in the NPT ensemble at 1 atm and 25°C. THF is a poorly structured liquid. Typical preferred orientation of molecules has been explored and calculations shown different types of molecular pairs exist concurrently in the liquid. The geometry of those pairs was deeply investigated and its influence in the liquid structure discussed. The lack of molecular organization in the liquid is closely related to the existence of that diversity of molecular pairs. Its geometry changes from antiparallel up to T-like depending on the distance between the molecules in the pairs.

Dependence of viscosity of Cu_9In_4 intermetallics melt on thermal history

The temperature dependence of the dynamic viscosity of Cu9In4 intermetallics melt has been investigated in five kinds of different heating and cooling processes with a torsional oscillation viscometer, It has been found that the viscosity of all Cu9In4 intermetallics decreases with increasing temperature in five kinds of different thermal processes. Thermal history has considerable effect on the viscosity. The viscosity in the cooling process with high superheating is greater than that in the cooling process with low superheating. The viscosity in the heating process is greater than that in the cooling process. No anomalous change in viscosity is measured in three kinds of cooling processes with low superheating. The anomalous change occurs at about 1050℃ in cooling with high superheating and at 800℃ in heating. Furthermore, the structural variation in different thermal processes has also been discussed on the basis of the change in viscosity and DSC analysis.

Effect of copper addition on the thermal contraction of indium melt clusters

The structure of In-1 %Cu and In-5%Cu (mass fraction) alloy melts werestudied at different temperatures above liquidus by using a high-temperature X-ray diffractometerand were compared with that of pure In melt. Experimental results show that with the addition of 1%Cu or 5% Cu, the thermal contraction phenomenon of atom clusters occurs in melts with thetemperature increasing like pure In melt. With the addition of 1% Cu, the thermal contraction ofatom clusters increases and the contraction is not homogeneous in the whole measurement temperaturerange. The sudden change and noticeable contraction can be found in the range of 280-390 ℃. Thetemperature range of the sudden change is lower than that of pure In melt. With the addition of 5%Cu, the thermal contraction of atom clusters decreases and the contraction is not consistent in thewhole measurement temperature range. The anomalous change can be measured at about 600 ℃. At thesame superheating temperature, the nearest interatomic distance r_1 of the melts containing copperis smaller than that of pure In melt, implying that the cluster structure of melts containing copperis more compact.

Molecular dynamics simulation of amorphous segregation in Ag-Rh alloys

Molecular dynamics simulation was carried out to investigate the liquid andamorphous microstructures of binary Ag_x-Rh_((100-x)) (x = 25, 50, 75 in atom fraction) alloys.Segregation feature of homogeneous interatomic binding of Ag-Rh liquid was found and probed, whichcan be retained into amorphous solids upon rapid cooling. Homogeneous binding may occur when thedifference in the elemental atomic sizes is less than 10%. The icosahedra in liquid before theformation of amorphous state exist in a stable state and the network formed by 1551-clusters inmolten alloys would inhibit the crystallization and diffusion of atoms. A higher degree of1551-clusters will be favorable to form metallic glasses.

Viscosities and their correlations with structures of Cu–Ag melts

The viscosities of a series of Cu–Ag melts in a temperature range from 1473 K to nearly liquid temperatures are measured by using an oscillating viscometer. At the same temperature, the value of viscosity increases first with silver content increasing, and reaches a maximum value at the eutectic component Cu40Ag60, then decreases. All the temperature dependences of the viscosities of Cu–Ag melts conform with the Arrhenius equation. The parameters of correlation length D of the studied Cu–Ag melts are calculated according to the experimental results of x-ray diffraction. The temperature dependence of correlation length D shows an exponential decay function, which is similar to the Arrhenius equation. Based on the values of viscosities and correlation length D, a direct correlation between viscosity and liquid structure is found for the investigated Cu–Ag melts through comparative analysis.

MEDIUM-RANGE ORDER CLUSTERS IN Fe-2.0%C ALLOY MELT

The structure of Fe-2.0%C alloy melt was investigated at 1580, 1560, 1540 and 1450℃ by using an X-ray diffractometer respectively. The results showed that with decreasing temperature, the average atoms of cluster, the coordination numbers, the correlation radius and the atom density increased, whereas the pre-peak of the structure factors curve remained almost at the same position. The appearance of the pre-peak indicated that the liquid structure and the solid structure of the Fe-2.0%C alloy were correlated.

Crystal structure and thermal decomposition kinetics of1-(pyridinium-1-yl)propane-(1-methylpiperidinium)bi[bis(trifluoromethanesulfonyl)imide], [PyC_3Pi][NTf_2]_2

The structure of a room temperature asymmetrical dicationic ionic liquid （ADIL）, 1-（pyridinium-l-yl） propane- （1-methylpiperidinium） bi[bis（tfifluoromethanesulfonyl）imide] （[PyC3Pi][NTf2]2）, was studied by the X-ray difo fraction method. Meanwhile, thermal analysis of [PyC3Pi][NTf2]2 was also studied using non-isothermal thermo- gravimetric analysis （TGA）. The title crystal belongs to the triclinic with space group Pi and unit-cell parameters a ： 0.95217 （8） nm, b = 1.05129 （11 ） nm, c = 1.70523 （14） nm, ct = 89,759 （8）°,β = 80.657 （7）°, γ=68.007 （9）°, and F（000） = 792. Thermal stability and thermal decomposition kinetics of the title compound were also investigated using TGA under the atmosphere of highly pure nitrogen. Heating curves at different rates were cor- related with kinetic equations Friedman and ASTM （also called iso-conversion method）. The values of average activation E （kJ·mol^-1 ） and pre-exponential constant lgA are 149.58 kJ. mol- 1 and 8.83, respectively, which were obtained by the two methods. The kinetic model function, activation energy and pre-exponential constant of this reaction using the multivariate non-linear-regression method were f（a） = （1 -a）（1 ＋ 4.1870a）, 151.04 kJ·mol^-1 and 8.81, respectively, which were basically consistent with iso-conversion methods.