Tsutomu Yamamura

Viscosities of Fe–Ni, Fe–Co and Ni–Co binary melts

Viscosities of three binary molten alloys consisting of the iron group elements, Fe, Ni and Co, have been measured by using an oscillating cup viscometer over the entire composition range from liquidus temperatures up to 1600 °C with high precision and excellent reproducibility. The viscosities measured showed good Arrhenius linearity for all the compositions. The viscosities of Fe, Ni and Co as a function of temperature are as follows: The isothermal viscosities of Fe–Ni and Fe–Co binary melts increase monotonically with increasing Fe content. On the other hand, in Ni–Co binary melt, the isothermal viscosity decreases slightly and then increases with increasing Co. The activation energy of Fe–Co binary melt increased slightly on mixing, and those of Fe–Ni and Ni–Co melts decreased monotonically with increasing Ni content. The above behaviour is discussed based on the thermodynamic properties of the alloys.

Density Measurement of Molten Silicon by a Pycnometric Method

The density of molten silicon was measured using a newly developed pycnometer made of boron nitride. The present method has many advantages for measuring the density of molten silicon, which has a high temperature and can be easily oxidized. The pycnometer was precisely machined, and its volume at high temperatures was acculately determined. The procedure to overflow the excess melt was carried out in a closed apparatus under a helium atmosphere. A special procedure was introduced to avoid the error generated by the volume expansion of silicon when it solidified. The total uncertainty of the measurement was estimated to be within 0.5%. The measured density showed a linear relationship with respect to temperature and agreed well with literature values. The expansion coefficient of molten silicon was similar to those of typical molten metals in spite of the low expansion coefficient of solid silicon. This suggested that the structural change of molten silicon was similar to those of typical metals.

R&D of a MW-class solid-target for a spallation neutron source

Abstract R&D for a MW-class solid target composed of tungsten was undertaken to produce a pulsed intense neutron source for a future neutron scattering-facility. In order to solve the corrosion of tungsten, tungsten target blocks were clad with tantalum by means of HIP’ing, brazing and electrolytic coating in a molten salt bath. The applicability of the HIP’ing method was tested through fabricating target blocks for KENS (spallation neutron source at KEK). A further investigation to certify the optimum HIP conditions was made with the small punch test method. The results showed that the optimum temperature was 1500 °C at which the W/Ta interface gave the strongest fracture strength. In the case of the block with a hole for thermocouple, it was found that the fabrication preciseness of a straight hole and a tantalum sheath influenced the results. The development of a tungsten stainless-steel alloy was tried to produce a bare tungsten target, using techniques in powder metallurgy. Corrosion tests for various tungsten alloys were made while varying the water temperature and velocity. The mass loss of tungsten in very slow water at 180 °C was as low as 0.022 mg/y, but increased remarkably with water velocity. Simulation experiments for radiation damage to supplement the STIP-III experiments were made to investigate material hardening by hydrogen and helium, and microstructures irradiated by electrons. Both experiments showed consistent results on the order of the dislocation numbers and irradiation hardness among the different tungsten materials. Thermal-hydraulic designs were made for two types of solid target system of tungsten: slab and rod geometry as a function of the proton beam power. The neutronic performance of a solid target system was compared with that of mercury target based on Monte Carlo calculations by using the MCNP code.

Electrochemical study of the mechanism of formation of the surface alloy of aluminum–niobium in LiCl–KCl eutectic melt

Abstract This work aims to describe the reduction mechanism by which niobium–aluminum alloys are formed in LiCl–KCl eutectic melt. The electrochemical reduction of AlCl 3 at an inert electrode such as tungsten and at a niobium electrode, and the electroreduction of AlCl 3 and Nb 3 Cl 8 simultaneously were investigated by cyclic voltammetry, convolution voltammetry and chronoamperometry. At a tungsten electrode, AlCl 3 was reduced to metallic aluminum via a quasi-reversible process involving a three-electron process. At a niobium electrode, AlCl 3 showed very complex behaviour: underpotential deposition of aluminum followed by formation of a surface alloy of aluminum–niobium occurring at 540 and 180 mV above the pure aluminum deposition potential, respectively. The electroreduction of AlCl 3 and Nb 3 Cl 8 , both present in the LiCl–KCl, confirmed these observations. From chronoamperometric measurements it was suggested that the niobium electroactive species is not reduced to the metallic form until the co-deposition of aluminum begins.

Viscosity of Molten GaSb and InSb

Viscosities of molten GaSb and InSb as III–V compound semiconductors were measured using an oscillating viscometer to study the thermophysical properties of semiconductor melts. A specially designed quartz crucible was used to prevent the evaporation of Sb from the melts. The measurements were performed in the temperature ranges from the melting point to about 1490 K for GaSb and from supercooled temperatures to about 1340 K for InSb. The viscosities obtained for both GaSb and InSb showed good Arrhenius linearity despite their wide temperature ranges. The activation energies of GaSb and InSb were almost the same, although the absolute viscosity of GaSb was slightly higher than that of InSb. It was concluded that most semiconductors including Si and Ge show Arrhenius behavior and have a low viscosity. The reason for the low viscosity is considered to be related to their melt structure, which may be similar to that of molten metals with low melting points.

Corresponding-states data correlations and molten salts viscosities

Transport properties of molten salts are encountered in a broad range of R&D tasks, particularly in areas of high-temperature thermal energy storage and in advanced battery concepts. This communication examines a semiempirical corresponding-states correlation as a predictive method using molten salts viscosities. Predictive calculations with molten NaCl and KNO3 as model systems, and with calibration quality data sets as the reference base, are used to evaluate this method. While the proper slope for the temperature dependence is “forecast,” the quality of the predicted data depend directly on the accuracy level of the one experimental value that is the seed for the calculations. Some results are described to show how such calculatins have proved useful in guiding value judgments in studies of the viscosity data in the open scientific literature.

High temperature 1H NMR study of proton conducting oxide SrCe0.95Y0.05H0.004O3-δ

Abstract The ionic motion of protons in yttrium doped SrCeO 3 perovskite has been investigated by means of high temperature 1 H NMR and ac electric conductivity measurements. The temperature dependences of line shapes and spin–lattice relaxation times ( T 1 ) were obtained. The inverse temperature versus logarithm of T 1 plot shows asymmetric temperature dependence with respect to its minimum value, and was well interpreted using the classical Bloembergen, Purcell and Pound (BPP) formula with introducing distributions of the activation energies. The averaged correlation times of the proton hopping were obtained from the T 1 data. The conductivity calculated from the Einstein equation using NMR correlation times assuming the jump distance of proton hopping as 1 A yields quantitative agreement with the measured conductivity in a wide temperature range.

Thermophysical properties of molten salts: Hypersonic velocities of molten alkali nitrates and their mixtures

By means of Brillouin scattering spectroscopy, hypersonic velocities in NaNO3-KNO3 binary melts have been measured at temperatures from the liquidus temperatures of the melts to 200 K above them over the entire range of compositions. The light beam scattered by the melt is analyzed with a pressure-scanned Fabry-Perot spectrometer. The hypersonic velocities obtained are about the same as the ultrasonic velocities reported at compositions rich in NaNO3, but are markedly larger than those at compositions rich in KNO3, indicating the occurrence of structural relaxation. Thermodynamic values such as adiabatic and isothermal compressibilities, constant-volume heat capacity, and internal pressure calculated from the sound velocity obtained show that the melt can be treated as a typical ionic liquid, though it contains a certain amount of associated species.

Spin-glass behavior in CeCu2-type uranium compound U2AuGa3

We present the results of ac and dc susceptibility, magnetization, magnetic relaxation, specific heat, and electrical resistivity measurements on U2AuGa3, an orthorhombic CeCu2-type nonmagnetic atom disorder system. These data clearly indicate that U2AuGa3 undergoes a spin glass phase transition at a static freezing temperature Ts=23.6K, in spite of the lack of triangular magnetic structure. It is observed that the variation of the characteristic temperature Tir (the bifurcation point between field-cooled and zero-field-cooled susceptibilities) with applied field H for U2AuGa3 is not consistent with the “AT line,” but follows a Tir∝−H2∕5 law. The observed spin glass behavior and the formation of frustrated magnetic interactions in U2AuGa3 are discussed in a magnetic cluster model.

Viscosities of molten alkali-metal bromides and iodides

Viscosities of molten alkali-metal bromides and iodides, whose reported values are scattered, have been measured by the use of a capillary viscometer made of quartz which is newly designed to obtain a high precision. The viscometer consists of the quartz capillary with a funnel of the suspended level type, and the melt is sealed in it under vacuum. The total error in the measurement is estimated to be within 0.7% at high temperatures. Viscosities of all the alkalimetal bromides and iodides show similar values at a constant temperature. Viscous flow behaviors of all the alkali-metal halides are discussed based on the activation energy and the hard sphere model. The apparent activation energy increases with an increase in the melting temperature of the salt. The viscosity of the alkali-metal halide melt at the melting temperature increases as the ratio of hard sphere volume to hole volume calculated from the surface tension.