Investigation of surface properties of liquid transition metals: Surface tension and surface entropy

In the present study, surface properties namely surface tension and surface entropy of liquid transition metals have been reported. The surface entropy of liquid Fe, Co and Ni metals has been investigated using the expression derived by Gosh et al. [R.C. Gosh, A.Z. Ziauddin Ahmed, G.M. Bhuiyan, Eur. Phys. J. B 56 (2007) 177]. To describe interionic interaction the pseudopotential approach has been used and radial distribution functions have been determined from the solution of Ornstein-Zernike integral equation. The calculated values of surface tension and surface entropy agree well with experiment. The present study shows that the expression derived by Gosh et al. leads to a good estimation for the surface entropy.     

利用ICP-MASS研究有机培肥土壤重金属淋溶特征

以下辽河平原11年长期定位试验为平台,采用原状土柱淋溶实验,通过比较不同用量有机肥处理土壤重金属积累情况及其淋溶特征,探讨了雨养农业条件下有机培肥措施对土壤表层重金属（Cu,Zn,Cd和Cr）积累的影响,阐述了重金属在土壤表层(0～20 cm)中的积累特征明确了重金属元素的淋溶特点和垂直迁移规律(0～60 cm)。研究表明,随着有机肥用量增加,表层土壤中Cu,Zn,Cd和Cr的含量都随之升高,积累速度为Cd＞Cu＞Zn＞Cr。根据中国土壤环境质量标准(GB15618-1995),即使施入50 t·ha-1有机肥料,也未造成表层土壤Cr, Cu和Zn的污染,其中Cr仍符合Ⅰ类土壤质量标准,而Cu和Zn符合国家Ⅱ类土壤质量标准,但对Cd而言,此时表层土壤含量已接近国家Ⅲ类土壤质量标准阈值,存在较大风险,应引起足够重视。土柱淋溶实验表明,只有个别淋溶液Cu和Cd浓度属于国家Ⅲ类水质量标准（GB/T14848—93）,其余均符合国家Ⅱ类及以上水质标准,且所有淋溶液Cr的含量都符合国家Ⅰ类水质标准,表明在下辽河平原,即使有机肥使用量达到50 t·ha-1时,仍未对地下水构成任何风险。另外,淋溶液中的重金属含量均随土层深度增加呈现下降趋势(Cr除外),表现出重金属不易下移的特点,但相对而言,Zn和Cr向深层土壤淋溶能力较强,Cu和Cd则更易积累在表层土壤。     

An effective method for hard sphere diameters of real fluids along the coexistence line vapour-liquid

The variation of the effective hard sphere diameter with the temperature along the equilibrium line vapour-liquid has been analyzed for a great variety of substances including: (a) atomic simple liquids; (b) inorganic and organic molecular liquids and (c) liquid metals, following several procedures, based in the analogy with a hard sphere fluid. Though the comparison among available methods is generally satisfactory, the method based on internal pressure seems to be more effective.     

Calculation of the surface energy of hcp-metals with the empirical electron theory

A brief introduction of the surface model based on the empirical electron theory (EET) and the dangling bond analysis method (DBAM) is presented in this paper. The anisotropy of spatial distribution of covalent bonds of hexagonal close-packed (hcp) metals such as Be, Mg, Sc, Ti, Co, Zn, Y, Zr, Tc, Cd, Hf, and Re, has been analyzed. And under the first-order approximation, the calculated surface energy values for low index surfaces of these hcp-metals are in agreement with experimental and other theoretical values. Correlated analysis showed that the anisotropy of surface energy of hcp-metals was related with the ratio of lattice constants (c/a). The calculation method for the research of surface energy provides a good basis for models of surface science phenomena, and the model may be extended to the surface energy estimation of more metals, alloys, ceramics, and so on, since abundant information about the valence electronic structure (VES) is generated from EET.     

广州珠江水体微表层与次表层中重金属的分布特征

采用ICP-AES对广州珠江水体微表层与次表层中Cu、As、Zn、Cr、Pb和Cd的质量浓度进行为期一年的调查研究。结果表明：珠江广州段水体均不同程度地受到6种重金属的污染,重金属浓度的季节性变化比较明显,在春季和冬季时浓度较高,夏季时浓度较低;重金属浓度的空间变化也比较明显。除Zn外,微表层对其余5种重金属均具有较强的富集作用。     

Calculation of entropy of mixing of liquid metal alloys in a hard sphere system

A semi-empirical model, based on the hard sphere system, is used to determine the entropy of mixing of simple as well as compound-forming alloys. For the compound-forming liquid solutions, the method leads to fairly accurate results, showing thereby that the usual theory of hard spheres mixtures can be applied to compound forming alloys also. It has been shown that the compound formation is very sensitive to the temperature of the mixture. Numerical applications are attempted for NaHg and NaGa.     

Structure factor of liquid metals in one-component plasma system

We present the analytical expression to determine the static structure factorS(q) of liquid alkali metals based on the semi-analytic theory of Baus and Hansen. The calculations were motivated to point out the anomalies exhibited by one-component plasma system (ocp) in describing the structure factor. The numerical example of Na illustrates our results.ocp structure factor is also compared with those obtained by the hard sphere system.     

Universal Scaling Law for Atomic Diffusion and Viscosity in Liquid Metals

The recently proposed scaling law relating the diffusion coefficient and the excess entropy of liquid [Samanta A et al. 2004 Phys. Reu. Lett. 92 145901; Dzugutov M 1996 Nature 381 137], and a quasi-universal relationship between the transport coefficients and excess entropy of dense fluids [Rosenfeld Y 1977 Phys. Rev. A 15 2545],are tested for diverse liquid metals using molecular dynamics simulations. Interatomic potentials derived from the glue potential and second-moment approximation of tight-binding scheme are used to study liquid metals.Our simulation results give sound support to the above-mentioned universal scaling laws. Following Dzugutov,we have also reached a new universal scaling relationship between the viscosity coefficient and excess entropy.The simulation results suggest that the reduced transport coefficients can be expressed approximately in terms of the corresponding packing density.     

Hydrophobic/hydrophilic solvation: inferences from Monte Carlo simulations and experiments

In this study Monte Carlo simulations are used to determine the solvation properties of model hydrophobic (xenon and hard sphere) and hydrophilic (dimethyl ether) solutes in SPC/E water. Various contributions to the experimental solvation entropy, including the solvent reorganization entropy, have been determined. The main conclusion drawn, which is in accord with solubility data, is that poor solubility correlates with poor solute-water interaction. At room temperature, energy dominates the aqueous solubility of both hydrophobic and hydrophilic solutes, rather than entropy. However, at higher temperatures the solubility can pass through a minimum, and then entropy becomes dominant. Another interesting finding is the presence of larger than expected cavities in water. Two different simulation results support this finding. This unexpected hollow structure in water explains why a hard sphere solute is more soluble in water than in a comparable hard sphere or Lennard-Jones solvent. Hydrogen bonding causes water to aggregate into clusters that produce a few large cavities rather than many smaller cavities. The propensity for clustering also explains why water gives the illusion of being a low density liquid. Sufficient theoretical apparatus is developed to connect theoretical solvation properties to those measured by simulation and experiment. Finally, based on gas solubility, an intuitive hydrophobic/hydrophilic scale is developed.     

Structure factor of a system with shouldered hard sphere potential

The structure factor of a system of particles interacting through a shouldered hard sphere potential is computed from a Monte Carlo simulation. The result pleads for a similar effective two-body potential in liquid metals like bismuth and confirms previous conclusions of Silbert and Young.     

A phenomenological explanation for the buckling of surface alloys

A phenomenological model, in which the interactions between the nearest-neighbor (NN) atoms are described as bondings but not hard sphere contacts, is proposed to explain the unexpected reduced buckling in surface alloy systems. In the model, the forces acting on an adsorbate atom from its NN substrate atoms in different layers may be either repulsive or attractive, depending on whether the bond between the adsorbate atom and its NN substrate atoms is compressed or stretched. It is found that the forces on the adsorbate atom from its NN substrate atoms in the sub-surface layer play a more important role for the buckling of surface alloy than those from its NN substrate atoms in the surface layer do. The bucklings expected by the model are significantly smaller than those predicted by the simple hard sphere model and are in good agreement with the experiments when the equilibrium bond length of the NN adsorbate-substrate atom pairs is taken as the sum of the corresponding metal radii.     

Calculation of electrical resistivity of Mg,Cd, and Zn in solid and liquid state. local pseudopotential approximation

Pseudopotential method, thermodynamic perturbation theory, and the formula due to Ziman are used for calculating the temperature dependence of the electrical resistivity of solid and liquid Mg, Cd, and Zn. In solid metals, a system of Einstein oscillators is chosen as the ground state, and in melts, solid spheres are chosen. Electrical resistivity of a solid metal is represented by a sum of a diffusion and a continuous contribution, with the latter practically completely determining the temperature dependence of electrical resistivity. The local pseudopotential approximation is found to be sufficiently correct for calculating the electrical resistivity of Mg; however, it gives lower values of electrical resistivities of Cd and Zn, which is due to neglecting hybridization effects.Translated from Izvestiya Vysshikh, Uchebnykh Zavedenii, Fizika, No. 3, pp. 93–100, March, 1984.     

An improved way of minimizing free energy in the variational method with the square well reference system

For the variational method of the thermodynamic perturbation theory with the square well reference system to which the semianalytical way of solving the mean spherical approximation is applied, a new way of minimizing the free energy is proposed. The approach is applied to liquid sodium and potassium, the effective pair interaction in which is described within the framework of the pseudopotential theory. For each of the metals under study, the global minimum of the free energy was found as a function of two independent variables (the hard core diameter and the mean atomic volume). In this minimum, a better agreement between the calculation results and the experimental data is obtained than when using the hard sphere reference system.     

ICP-MS研究太湖过滤水和表层沉积物中重金属的含量水平及污染评价

采用电感耦合等离子体质谱法(ICP-MS)对太湖22个采样点过滤水和18个采样点表层沉积物中镉(Cd)、铬(Cr)、铜(Cu)、镍(Ni)、铅(Pb)和锌(Zn)六种重金属元素含量进行测定。同时,采用单因子指数法(I_i)、内梅罗综合指数法(I)、地质累积指数法(I_geo)、潜在生态风险指数法(RI)和平均可能影响浓度商法(mPEC-Q)分别对过滤水和表层沉积物进行了污染评价。结果表明, 除S₃,S₄,S₂₀,S₂₂采样点外过滤水中Cu,Ni和Zn元素含量最高。其重金属平均含量水平大小排序为：Zn>Ni>Cu>Cr>Cd>Pb。研究区域的I_i和I值均小于1, 表明所有采样点五种重金属元素(Ni无标准限值)均处于清洁状态。而在表层沉积物中六种元素含量均超过当地背景值, 其平均含量大小排序为：Zn>Cr>Pb>Ni>Cu>Cd, 其中S₁₂采样点(渔民生态园)六种元素含量最高,且它们具有最大的I_geo,RI(327)和mPEC-Q(0.605),表明沉积物存在不同程度的污染。源分析的结果表明, 六种重金属具有较大的相关性,且Cd,Cu,Pb和Zn受电镀、冶炼工业生产及农业活动中化肥使用的影响较大。研究结果对追溯太湖重金属来源、迁移规律、生物效应和综合治理提供可信的实验依据。     

Surface tension modelling of liquid Cd–Sn–Zn alloys

The thermodynamic model in conjunction with Butler equation and the geometric models were used for the surface tension calculation of Cd–Sn–Zn liquid alloys. Good agreement was found between the experimental data for limiting binaries and model calculations performed with Butler model. In the case of ternary alloys, the surface tension variation with Cd content is better reproduced in the case of alloys lying on vertical sections defined by high Sn to Zn molar fraction ratio. The calculated surface tension is in relatively good agreement with the available experimental data. In addition, the surface segregation of liquid ternary Cd–Sn–Zn and constituent binaries has also been calculated.     

Phonon dispersion relation of liquid metals

The phonon dispersion curves of some liquid metals, viz. Na (Z = 1), Mg (Z = 2), Al (Z = 3) and Pb (Z = 4), have been computed using our model potential. The charged hard sphere (CHS) reference system is applied to describe the structural information. Our model potential along with CHS reference system is capable of explaining the phonon dispersion relation for monovalent, divalent, trivalent and tetravalent liquid metals.     

Surface energies of metals in both liquid and solid states

Although during the last years one has seen a number of systematic studies of the surface energies of metals, the aim and the scientific meaning of this research is to establish a simple and a straightforward theoretical model to calculate accurately the mechanical and the thermodynamic properties of metal surfaces due to their important application in materials processes and in the understanding of a wide range of surface phenomena. Through extensive theoretical calculations of the surface tension of most of the liquid metals, we found that the fraction of broken bonds in liquid metals (f) is constant which is equal to 0.287. Using our estimated f value, the surface tension (γ_m), surface energy (γ_SV), surface excess entropy (−dγ/dT), surface excess enthalpy (H_s), coefficient of thermal expansion (α_m and α_b), sound velocity (c_m) and its temperature coefficient (−dc/dT) have been calculated for more than sixty metals. The results of the calculated quantities agree well with available experimental data.     

Application of a radioactive tracer method for diffusion study in some liquids

In this paper a radioactive tracer technique based on sliding cell method developed in our laboratory for the study of diffusion in liquids is presented in detail. This method consists of radioactive and non-radioactive liquid columns of equal length and the radiation detector is placed in a vertical geometry over the diffusion column. Some liquid metals and aqueous electrolyte solutions were studied by this method. The data of liquid metals like mercury and gallium have been analyzed from the point of view of hard sphere model and those of electrolyte solutions from phenomenological theories. Onsager’s coefficientsL ₁₁,L ₁₂,L ₂₂ have been calculated from the experimental data and the variation of diffusion with solute concentration has been explained from ion-ion interaction.     

Quantum mechanical scaled particle theory of hard spheres at high temperature

The leading term of the high-temperature quantum corrections to the scaled particle theory of the hard sphere fluid have been obtained. This provides approximate corrections to the pressure, surface tension, and reversible work to create a spherical cavityW(r) of the quantum mechanical hard sphere fluid. A number of exact identities valid for the classical hard sphere fluid are shown to apply also to the quantum mechanical hard sphere fluid, including the fluctuation relation betweenW(r) and the probability of finding a cavity of radius at leastr.     

ICP-MS研究太湖表层沉积物对Cd2+和Zn2+的吸附-解吸特性

前期研究发现太湖过滤水和表层沉积物中Zn含量最高,且表层沉积物中Cd存在强生态危害。因此,在优化实验条件下,以电感耦合等离子体质谱(ICP-MS)为分析手段研究了太湖苏州湾大桥东表层沉积物(标记为SES)对Cd2+和Zn2+的吸附-解吸特性。吸附动力学结果表明：SES对Cd2+和Zn2+的吸附能力相差不大,在吸附时间t<120 min时,吸附是一个快速阶段,而当t≥120 min时则相反,吸附趋于动态平衡;Cd2+和Zn2+的吸附更符合伪二级动力学模型。吸附热力学实验表明,沉积物对Cd2+的吸附更符合Freundlich模型,而对Cd2+的吸附更符合Langmuir模型。沉积物中Cd2+和Zn2+的解吸动力学研究发现,二者均更符合Elovich方程,为非均相扩散过程。且当pH值增大时,沉积物中Cd2+和Zn2+的解吸量逐渐减小,并在pH=9时趋于稳定。结合Cd2+和Zn2+的吸附-解吸特性发现,SES对Cd2+和Zn2+的吸附速率远远大于其解吸速率,与作者前期研究结果一致。揭示了太湖表层沉积物对Cd2+和Zn2+的吸附-解吸作用机理及不同因素对吸附-解吸行为的影响。对研究太湖固-液两相界面重金属的分配和污染水体修复具有重要指导意义。