First-principles calculation of crystalline materials genome: a preliminary study

The US President Obama launched the Materials Genome Initiative on June 24,2011,aimed at speeding up the pace of discovering,developing,manufacturing,and deploying advanced materials by at least twice as fast as is possible at present,at a fraction of the cost with the help of existing advanced computer technology.According to the authors’understanding to the event,this article will first give a brief discussion on the origin of material genome,its scientific implication,research significance,and the far-reaching influence of materials genome study to the developments of materials science and human society.Then,the subsequent contents will introduce the research progresses of the related works carried out by the authors’research group over the last decade,on the first-principles studies of crystalline materials genome.The highlights are focused on the method implementations for configuration optimization of lattice structure,first-principles calculations of various physical parameters on elastic,electronic,dielectric,and thermodynamic properties,and simulations of phase transition and particle transport in solids.The technical details for extending these methods to low-dimensional crystalline materials are also discussed.The article concludes with an outlook on the prospect of materials genome research.     

Modeling of mass transfer characteristics of bubble column reactor with surfactant present

Danckwert‘s method was used to determine the specific interfacial area, a, and the individual mass transfer coefficient, κL, during absorption of CO2 in a bubble column with an anionic surfactant in the carbonate-bicarbonate buffer solution and NaAsO2 as catalyst, the presence of which decreases the specific interracial area and the individual mass transfer coefficient. The specific interfacial area and the individual mass transfer coefficient increase with increasing superficial gas velocity. The specific interfacial area decreases whereas the individual mass transfer coefficient increases with increasing temperature. The results of experiments were used to determine the dependence of a, κL, and κLa on the surface tension, the temperature of the absorption phase, and the superficial velocity of the gas. The calculated results from the correlation were found to be within 10% deviation from the actual experimental results.     

Constitutive modeling for unsaturated soils considering gas hardening effect

The influence of gases on unsaturated soils is discussed in the paper.First,the selection of stress state variables is discussed.It is shown that gas pressure as well as generalized effective stress and modified suction are required to construct a constitutive model of an unsaturated soil.The deformation mechanisms of solid,liquid and gas phases in soils are then investigated.It is realized that the deformation of gas phase interacts with the deformations of the other two phases in soils.Gas laws are used to describe the gas behavior.Similar to the other two phases in soil,the change of gas volume can be divided into an elastic part and a plastic part, and the latter part is then introduced to the soil hardening equation to reflect the impact of the gas on the soil.Then,a simple elasto-plastic model considering the gas effect for isotropic states is developed.Finally,the model predictions are given and compared with existing experimental data.A good agreement between them is found.Comparisons of the predictions between our model and Wheeler’s model are also performed.     

Thermodynamic properties and microstructural characteristics of binary Ag-Sn alloys

The liquidus and solidus temperatures and enthalpy of fusion for Ag-Sn alloys are systematically measured within the whole composition range by differential scanning calorimetry (DSC). The measured enthalpy of fusion is related to Sn content by polynomial functions, which exhibit one maximum value at 52 wt%Sn and two minimum values around 21 wt%Sn and 96.5 wt%Sn, respectively. The liquidus slope, the solidification temperature interval, the solute partition coefficient and the entropy of fusion are calculated on the basis of the measured results. The undercoolability of those liquid Ag-Sn alloys solidifying with primary (Ag) solid solution phase is stronger than the other alloys with the preferential nucleation of ζ and ε intermetallic compounds. Morphological observations reveal that peritectic reactions can rarely be completed, and the peritectic microstructures are always composed of both primary and peritectic phases.     

Gas-liquid phase coexistence and finite-size effects in a two-dimensional Lennard-Jones system

The gas-liquid phase coexistence in a two-dimensional Lennard-Jones system is investigated using Maxwell construction method together with molecular dynamics simulations.The results of phase coexistence in different truncations of the potential are compared with data obtained from the literature,and the corresponding critical properties calculated.The crossover from Ising-like to mean field behavior is observed and confirmed as the temperature approaches the critical point from below.Performing simulations on systems with different sizes,we find that a finite size effect is more significant than those shown in most of the previous results,and a lower critical temperature is obtained when the full extent of this finite size effect is considered.     

A first-principles study of displacive β to ω transition in Ti-V alloys

The ground state properties of β and ω phases in Ti-(0–30 at%)V alloys were calculated, and subsequently thermodynamics and energy barriers of the displacive β to ω transition were investigated by first-principles. The results show that the lattice parameters of β and ω phases decreases with increasing V content in Ti-V alloys. The principal lattice strains for the β to ω transition are highly compositional dependent, and the volume variation decreases with increasing V content. The mechanical stability of the ω phase increases initially at the V content around 10 at% and then decreases with increasing V content. Based on the quasiharmonic Debye model, a metastable diffusionless phase diagram has been established, showing that the ω phase is thermodynamically more stable than the β phase at room temperature, anticipating a spontaneous transition from β to ω phases in Ti-V alloys. The calculations of energy pathways indicate that there is an energy barrier during the displacive βto ω transition in Ti-V alloys at temperatures from 100 to 500 K, but not at 0 K.     

The materials genome and CALPHAD

The mapping of the human genome is an important basis for the development of new medicals and medical treatments.Consequently,it has attracted tremendous research funding over the last decade.On June2011,the Materials Genome Initiative was announced by the US President Obama as collaboration on modeling and advanced materials databases.Unfortunately,the materials genome was given a rather vague definition in the announcement.However,the materials genome should be defined in analogy with biological genomes and one may then conclude that:at any moment,the performance of a specific material depends on its chemical composition(inherent property stored in its genome)and its environment(external interactions–processing–conditions during usage).The materials genome should thus be defined as a set of information encoded in the language of thermodynamics obtained by careful assessment of experimental data and quantum mechanical calculations from which certain conclusions about the material can be drawn.The CALPHAD databases contain the thermodynamic and kinetic properties of a materials system.Such databases allow the prediction of materials structure as well as its response to processing and usage conditions,and are major parts of integrated computational materials engineering.     

Softening–melting behavior of mixed burden based on low-magnesium sinter and fluxed pellets

A low MgO content in sinter is conducive to reduce the MgO content in blast furnace slag.This study investigated the effect of MgO content in sinter on the softening–melting behavior of the mixed burden based on fluxed pellets.When the MgO content increased from 1.31 wt% to 1.55 wt%, the melting temperature of sinter increased to 1521℃.Such an increase was due to the formation of the high-meltingpoint slag phase.The reduction degradation index of sinter with 1.31 wt% MgO content was better than that of others.The initial softening temperature of the mixed burden increased from 1104 to 1126℃ as MgO content in sinter increased from 1.31 wt% to 1.55 wt%, and the melting temperature decreased from 1494 to 1460℃.The permeability index(S-value) of mixed burden decreased to 594.46 kPa·℃ under a high MgO content with 1.55 wt%, indicating that the permeability was improved.The slag phase composition of burden was mainly akermarite(Ca_2MgSiO_7) when the MgO content in sinter was 1.55 wt%.The melting point of akermarite is 1450℃, which is lower than other phases.     

Effect of heat treatment on the microstructure and micromechanical properties of the rapidly solidified Mg61.7Zn34Gd4.3 alloy containing icosahedral phase

In this paper, the microstructure evolution of the rapidly solidified (RS) Mg_61.7Zn₃₄Gd_4.3 (at%, atomic ratio) alloy at high temperatures was investigated. The hardness and elastic modulus of the main precipitated phases were also analyzed and compared with those of the α-Mg matrix on the basis of nanoindentation tests. The results show that the RS alloy consists of either a petal-like icosahedral quasicrystal (IQC) phase (~20 μm) and block-shaped H1 phase (~15 μm) or IQC particles with an average grain size of~107 nm as well as a small proportion of amorphous phase, which mainly depends on the holding time at the liquid temperature and the thickness of the ribbons. The IQC phase gradually transforms at 400℃ to a short-rod-shaped μ-phase (Mg_28.6Zn_63.8Gd_7.7) with a hexagonal structure. The hardness of the IQC phase is higher than that of H1 phase, and both phases exhibit a higher hardness than the α-Mg matrix and the μ-phase. The elasticity of the H1 phase is superior to that of the α-Mg matrix. The IQC phase possesses a higher elastic modulus than H1 phase. The easily formed H1 phase exhibits the poorest plastic deformation capacity among these phases but a higher elastic modulus than the α-Mg matrix.     

养护湿度对充填体性能的影响规律

Cemented paste backfill (CPB), a mixture of tailings, binder, and water, is widely and extensively used for the recovery of mineral resources, the prevention of ground subsidence, and the management of mine waste. When installed, the CPB is subjected to complex environmental conditions such as water content, temperature, and power, which have a significant impact on its efficiency. Thus, this study conducts a series of laboratory programs, including investigation of moisture, temperature, stress–strain relation, and microstructure to show the effect of curing humidity on the CPB behaviors. The results obtained indicate that ambient humidity can have a dramatic effect on CPB in terms of its macro performance of internal relative humidity, temperature and strength, as well as the micro expression. Typical examples of these effects on CPB include an increase in curing humidity, which favors binder hydration, and then an increase in hydration materials, temperature and peak stress in the CPB. The results obtained will lead to a better understanding of CPB’s responses to various environmental conditions.     

The entropy characters of point mutation

The biological diversity, which depends on the genetic material DNA, is the foundation for a species to survive and evolve. The entropy is the best measurement of biological diversity. Based on the single-parameter and the two-parameter models, here we established some differential equations about the point mutation of a DNA sequence with finite length, as well as some functions describing the processes of the variation in quantities of 4 kinds of bases （A, T, G and C） in the DNA sequence. At the molecular level, we discussed the entropy characteristics of point mutation. The results proved that a species maintained its entropy and evolved in the direction of the increasing biological diversity. In order to testify the theoretical results, we did a series of computer simulations of random point mutation in Matlab environment. The results were well consistent with the theoretical researches.     

Thermal treatment and utilization of Al-rich waste in high calcium fly ash geopolymeric materials

The Al-rich waste with aluminium and hydrocarbon as the major contaminant is generated at the wastewater treatment unit of a polymer processing plant. In this research, the heat treatment of this Al-rich waste and its use to adjust the silica/alumina ratio of the high calcium fly ash geopolymer were studied. To recycle the raw Al-rich waste, the waste was dried at 110℃ and calcined at 400 to 1000℃. Mineralogical analyses were conducted using X-ray diffraction (XRD) to study the phase change. The increase in calcination temperature to 600, 800, and 1000℃ resulted in the phase transformation. The more active alumina phase of active θ-Al₂O₃ was obtained with the increase in calcination temperature. The calcined Al-rich waste was then used as an additive to the fly ash geopolymer by mixing with high calcium fly ash, water glass, 10 M sodium hydroxide (NaOH), and sand. Test results indicated that the calcined Al-rich waste could be used as an aluminium source to adjust the silica/alumina ratio and the strength of geopolymeric materials. The fly ash geopolymer mortar with 2.5wt% of the Al-rich waste calcined at 1000℃ possessed the 7-d compressive strength of 34.2 MPa.     

基于低镁烧结矿和熔剂性球团的综合炉料熔滴性能研究

A low MgO content in sinter is conducive to reduce the MgO content in blast furnace slag. This study investigated the effect of MgO content in sinter on the softening–melting behavior of the mixed burden based on fluxed pellets. When the MgO content increased from 1.31wt% to 1.55wt%, the melting temperature of sinter increased to 1521°C. Such an increase was due to the formation of the high-melting-point slag phase. The reduction degradation index of sinter with 1.31wt% MgO content was better than that of others. The initial softening temperature of the mixed burden increased from 1104 to 1126°C as MgO content in sinter increased from 1.31wt% to 1.55wt%, and the melting temperature decreased from 1494 to 1460°C. The permeability index (S-value) of mixed burden decreased to 594.46 kPa·°C under a high MgO content with 1.55wt%, indicating that the permeability was improved. The slag phase composition of burden was mainly akermarite (Ca₂MgSiO₇) when the MgO content in sinter was 1.55wt%. The melting point of akermarite is 1450°C, which is lower than other phases.     

Understanding atomic-scale phase separation of liquid Fe-Cu alloy

Using liquid Fe 60 Cu 40 alloy as a model, the structure of liquid Fe-Cu alloy systems is investigated in the temperature range 1200 2200 K, covering a large metastable undercooled regime, to understand the phase separation of liquid Fe-Cu alloys on the atomic scale. The total pair distribution functions (PDFs) indicate that liquid Fe 60 Cu 40 alloy is ordered in the short range and disordered in the long range. If the atom types are ignored, the total atom number densities and PDFs demonstrate that the atoms are distributed homogenously in the liquid alloy. However, the segregation of Fe and Cu atoms is very obvious with decreasing temperature. The partial PDFs and coordination numbers show that the Cu and Fe atoms are not apt to get together on the atomic scale at low temperatures; this will lead to large fluctuations and phase separation in liquid Fe-Cu alloy.     

Meteorological observations on Mount Everest in 2005

Mount Everest, the highest point on the Earth is often referred to as the earth’s third pole as such the place is relatively inaccessible and little is known about its meteorology. In April 2005, an automatic weather station was installed at the mountain’s North Col (6523 m a.s.l.). According to the observational 10-minute mean and daily records, the meteorological characteristics were analyzed. All the meteorological elements displayed obvious diurnal variations during May 1 to July 22, 2005. The monthly variation of daily meteorological elements on Mount Everest coincided with that on Dingri, the closest routine meteorological station, with the high correlation coefficients of 0.928, 0.877, 0.682, 0.755, 0.826 and 0.676 (n=83, p＜ 0.001) for mean temperature, minimum temperature, maximum temperature, relative humidity, pressure and wind speed, respectively. Furthermore, the vertical mean gradient of temperature was above 0.6℃/100 m, especially for the daily maximum temperature. Most weather events on Mount Everest prominently appeared on the same day as those on Dingri, especially those from daily mean pressure, temperature and relative humidity with the cross-correlation coefficients of 0.673, 0.485 and 0.487 (n=83, p＜ 0.001), respectively. Some other weather events on Mount Everest lagged one-day behind those on Dingri. Furthermore, forecasting of the weather events on Mount Everest from pressure on Dingri was more reliable than those from the other meteorological elements. The conclusions are much important for research on meteorology and climate changes in the region.     

Study on constant-pressure specific heat of non-equilibrium phase change process in gas-liquid two-phase flow system

In this paper,the air-water vapor-water system is taken as an example,and the formula of constant-pressure specific heat during non-equilibrium phase change process in the two-phase flow system is deduced using the theory of two-phase flow and thermophysics. The constant-pressure specific heat of non-equilibrium phase change process is calculated with the corresponding numerical model,and the numerical results are compared to those of the equilibrium phase change process. It is shown that in evaporation process,the variational rate of the non-equilibrium specific heat increases with increasing initial fluid temperature and particle mass fraction. The smaller particle radius is,the faster the varia-tional rate is. Meanwhile,the constant-pressure specific heat of equilibrium process is higher than that of the non-equilibrium process all the time.     

Nonequilibrium Thermodynamic and Dissipative Structure Mechanism of Fluidized Beds

Fluidized beds are nonlinear dynamic systems that exchange mass and energy with outside. They are governed not only by fluid dynamics, but by thermodynamics, especially the second law of thermodynamics as well. According to Prigogine's dissipative structure theory, the following have been concluded: (1) a fixed bed is on thermodynamic blanch, and bubbling, turbulent and fast beds are on the dissipatve structure branches. (2) Entropy in fluidized beds is divided into two parts: entropy production and entropy flux. The latter increases with gas velocity and decreases with pressure of the systems. That means the entropy of a system may reduce and the system with higher gas velocity behaves as dissipative structure characteristics. (3) For a given velocity, a fluidized bed operates stably on the whole, but it is unstable to local gas-solid phases. The unstable phases are described by fluid dynamic equations, While the minimum of system energy function assures whole stability of the system. (4) A transition criterion of a bubbling bed is derived from Prigogine's stability theory.     

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.     

Constituent phases of the passive film formed on 2205 stainless steel by dynamic electrochemical impedance spectroscopy

The passive film formed on 2205 duplex stainless steel (DSS) in 0.5 M NaHCO₃+0.5 M NaCl aqueous solution was characterized by electrochemical measurements, including potentiodynamic anodic polarization and dynamic electrochemical impedance spectroscopy (DEIS). The results demonstrate that there is a great difference between the passive film evolutions of ferrite and austenite. The impedance values of ferrite are higher than those of austenite. The impedance peaks of ferritic and austenitic phases correspond to the potential of 0.15 and 0.25 V in the low potential range and correspond to 0.8 and 0.75 V in the high potential range. The evolutions of the capacitance of both phases are reverse compared to the evolutions of impedance. The thickness variations obtained from capacitance agree well with those of impedance analysis. The results can be used to explain why pitting corrosion occurs more easily in austenite phase than in ferrite phase.