Toshio Itami

Thermophysical properties of liquid refractory metals: Comparison between hard sphere model calculation and electrostatic levitation measurements

Thermophysical properties of molten refractory metals (titanium, zirconium, hafnium, and niobium) have been measured using a containerless method. Using an in-house developed electrostatic levitator, the density, the heat capacity, the entropy, the surface tension, and the viscosity of liquid phases have been measured over a wide temperature range. The measured data showed good agreement with theoretical calculations based on the hard sphere model.

Electronic structure of liquid metals and alloys

Abstract The density of states and momentum distribution function in liquid Na–K, Ag–Au, Pb–Sn, Cu–Sn, Hg–Bi, Hg–In systems have been calculated on the basis of Edwards’ theory, using the complex energy approximation proposed by Ballentine. Various pseudopotentials and structure factors are used. It is found that the thickness of the Fermi shell for the alloys is larger than that for the pure components except for the Hg–In system. The curve of density of states at the Fermi energy is close to the free-electron value except for the Ag–Au systems, in which the modified Borchi and De Gennaro potentials are used, but its shape near the bottom of the band sometimes differs from the free-electron curve. The density of states of Hg, which has a small dip near the Fermi level when Evens’ model potential is employed, is rather free-electron-like, while the curve in the Hg–In system becomes more smooth.

Viscosity of liquid K-Hg alloys

Abstract The viscosity of liquid K-Hg alloys was measured over the whole concentration range from about 70° to 400°C. The observed data show a strong maximum at 27 at. % K, but no extreme value at 7 at. % K corresponding to the strong minimum observed in the thermoelectric power measurements. The experimental results are compared with calculated values obtained by the distribution function method for the viscosity of liquid mixtures. The interionic potentials are computed by means of the pseudopotential method, and the partial pair correlation functions are calculated by using not only the Percus-Yevick solutions for a mixture of hard-sphere fluids but also those corrected simply for the effect of charge transfer between Hg and K atoms. The calculation is in qualitative agreement with the experimental concentration dependence, suggesting the importance of effect of charge transfer among the atoms.

Application of simple model theories to thermodynamic properties of liquid transition metals

The simple one-component plasma (OCP) model has been applied to thermodynamic properties of liquid 3d transition metals. For comparison, the results calculated by the hard-sphere (HS) model are also given. The electronic contribution to the entropy and heat capacity has been considered by a rectangular model of the density of states. In spite of the simplicity of the models the calculated values of the entropy, S, the specific heat at constant volume, CV, and the compressibility chi T, are in good agreement with experiment. This indicates that the OCP model, like the HS model, is well suited as a reference liquid for liquid transition metals.

Measurements of diffusion coefficients of metallic melt under microgravity?current status of the development of shear cell technique towards JEM on ISS

The microgravity condition is one of the ideal conditions for the measurements of diffusion coefficients in high temperature melts because of the absence of convection in the liquid sample. Many kinds of experimental techniques, such as the long capillary method and the shear cell method, have been devised in ground based researches for the measurement of diffusion coefficient in such high temperature melts. Recently, the shear cell technique coupled with the microgravity condition was applied to the measurements of high temperature metallic melts. This technique enables us to measure the diffusion coefficient with high precision. In this paper, a brief discussion is given about the trends of previous diffusion experiments in space performed particularly by Japanese researchers. Recently, the Japanese space agency, JAXA, has developed the shear cell technique for future space experiments in JEM. The current status of the development of our shear cell technique is summarized and new results are presented as typical experiments on the ground by using test samples, for example, liquid silver–gold alloys.

Development of an electrostatic levitator for neutron diffraction structure analysis

An electrostatic levitation (ESL) furnace was designed for the neutron diffraction study of condensed matter. This apparatus is composed of an electrostatic levitator, a neutron inlet path with Cd slit, a 160 degree window for the scattered neutrons, a CO2 laser for sample heating, and an optical pyrometer for temperature measurements. A preliminary neutron diffraction experiment with this ESL was performed for polycrystalline alumina. The sample position could be controlled with an accuracy of ±0.1 mm. The observed Bragg peaks were in complete agreement with those derived from the lattice data of alumina obtained from the literature value. This indicates that this facility is attractive for the structural study of condensed matter without containers.

Structure of Liquid Ge at High Temperatures

Neutron diffraction measurements have been performed for liquid germanium over a wide temperature range from 1000°C to 1550°C. The structure factor of liquid germanium just above the melting point has a pronounced shoulder in the high momentum transfer region of the first peak, as also by our data confirmed. With increasing temperature, the position of the first peak moves slightly to a high value of Q and the shoulder becomes inconspicuous.

Self-diffusion under microgravity and structure of group IVB liquids

Abstract The self-diffusion coefficient, DS in liquid Sn was measured by a long capillary method in the microgravity environment of the space shuttle, and the validity of a microgravity effect was confirmed for the measurements of diffusion in melts with high melting temperatures. The data of this DS under microgravity were well reproduced by calculations, particularly in the case closely related to liquid structures. A systematic microgravity experiment is required to obtain further insight and to develop a model for diffusion in group IVB liquids.

Resistivity and Knight shift of liquid Li-Ga alloys

The electrical resistivity rho and the 7Li and 71Ga Knight shifts of liquid Li-Ga alloys were measured. The maximum value of rho on the isotherm at 775 K is 161.1 mu Omega cm at 32.6 at.% Ga. The temperature coefficient delta rho / delta T exhibits a negative minimum at this concentration. This value of rho for liquid Li-Ga alloys does not exceed values appropriate to the nearly free electron (NFE) model; resistivity values calculated by the Faber-Ziman formula are in fair agreement with experiment, though the peak position of the calculated isotherm of rho is shifted slightly to the Li-rich side. However, the experimental Knight shifts provide clear evidence of charge transfer from Li to Ga. The Knight shift KLi of 7Li decreases rapidly with the addition of Ga up to 30 at.% Ga where rho is maximum. Beyond this Ga concentration KLi becomes constant. On the other hand, the Knight shift of 71Ga, KGa, decreases almost linearly with the addition of Li up to 53 at.% Ga. This is attributed to increasing p character of the Ga conduction electrons if 7Li is added. For a more quantitative interpretation it will be necessary to incorporate charge transfer in the NFE model.

The Volume of Liquid Hg–Tl and Hg–Cs Alloys

The molar volume and the thermal expansion coefficient of liquid Hg–Tl and Hg–Cs alloys were measured by a picnometer method. The molar volume of liquid Hg–Tl alloys varies almost linearly with concentration, and that of liquid Hg–Cs alloys shows large negative deviations from the linear variation. The thermal expansion coefficient of liquid Hg–Cs alloys shows a slight hump in the dilute Cs concentration range. The concentration dependence of the molar volume of these liquid alloys calculated by a simple pseudopotential approach are qualitatively in good agreement with experiment.