Haruaki Matsuura

In Situ Experimental Evidence for a Nonmonotonous Structural Evolution with Composition in the Molten LiF−ZrF4 System

We propose in this paper an original approach to study the structure of the molten LiF-ZrF(4) system up to 50 mol % ZrF(4), combining high-temperature nuclear magnetic resonance (NMR) and extended X-ray absorption fine structure (EXAFS) experiments with molecular dynamics (MD) calculations. (91)Zr high-temperature NMR experiments give an average coordination of 7 for the zirconium ion on all domains of composition. MD simulations, in agreement with EXAFS experiments at the K-edge of Zr, provide evidence for the coexistence of three different Zr-based complexes, [ZrF(6)](2-), [ZrF(7)](3-), and [ZrF(8)](4-), in the melt; the evolution of the concentration of these species upon addition of ZrF(4) is quantified. Smooth variations are observed, apart from a given composition at 35 mol % ZrF(4), for which an anomalous point is observed. Concerning the anion coordination, we observe a predominance of free fluorides at low concentrations in ZrF(4), and an increase of the number of bridging fluoride ions between complexes with addition of ZrF(4).

Ion specific effects on the structure of molten AF-ZrF4 systems (A+ = Li+, Na+, and K+).

The structure of AF-ZrF(4) system (A(+) = Li(+), Na(+), K(+)) compounds in the liquid state is studied using an approach combining EXAFS spectroscopy with molecular dynamics simulations. A very good agreement is observed between the two techniques, which allows us to propose a quantitative description of the liquids. From the Zr(4+) solvation shell point of view, we observe a progressive stabilization of the 7-fold and then of the 6-fold coordinated complexes when passing from Li(+) to Na(+) and K(+) as a counterion. Particular attention is given to the systems consisting of 35 mol % of ZrF(4). At that particular composition, the ZrF(6)(2-) complex predominates largely whatever the nature of the alkali. The calculated vibrational properties of this complex are in excellent agreement with a previous Raman spectroscopy experiment on molten KF-ZrF(4). The most important differences are observed for the lifetime of these octahedral units, which increases importantly with the size of the monovalent cation. On a larger scale, an intense first sharp diffraction peak is observed for the Zr(4+)-Zr(4+) partial structure factor, which can be attributed to the correlations between the octahedral units formed.

Spectroscopic Study on Vibrational Nonequilibrium of a Microwave Discharge Nitrogen Plasma

We generate a microwave discharge nitrogen plasma using a rectangular waveguide and a quartz tube (30 mm i.d.) inserted along the vector of the electric field, with an adjustable short-circuited plunger. The typical discharge conditions used are as follows: microwave frequency 2.45 GHz, input power 550 W, nitrogen (99.5%) gas flow rate 0.01–1.6 l/min, and discharge pressure p=0.5–10 Torr. Electron temperature Te, and density ne are measured using a double probe. Vibrational temperature Tv is obtained from the population density of the vibrational exited states of N2 C 3Πu by spectroscopic examination. Rotational temperature Tr is obtained from a comparison of the rovibronic spectra observed experimentally with the calculated ones. It is found that Te0.5–2 eV, Tv0.45–1 eV, and Tr0.06–0.1 eV under the present pressure conditions, whereas ne1011–1012 cm-3 at a low discharge pressure, and ne108–109 cm-3 at a high discharge pressure. We discuss the measured vibrational populations by theoretical calculations in which the variation in their number density is expressed in terms of molecular processes in the nitrogen plasma.

Spectroscopic study on vibrational distribution of N2 C3π and B3π states in microwave nitrogen discharge

We examined the vibrational and rotational temperatures of the C3Π and B3Π states of N2 by optical emission spectroscopy. We measured the band spectra (first and second positive systems) of N2 compared the experimentally measured and the calculated spectra to determine the actual vibrational and rotational temperatures of the generated plasma. We generated a microwave discharge nitrogen plasma in a cylindrical quartz tube (26 mm i.d.) with a discharge pressure of 0.5–1.0 Torr. The microwave frequency was 2.45 GHz and the output power was set at 600 W. It was found that Tv≈0.5–0.7 eV and Tr≈0.07–0.15 eV at B3Π (v=7, 8 and 9), whereas Tv≈0.65–0.9 eV and Tr≈0.06–0.16 eV at C3Π (v=0 and 1). We also discussed the measured vibrational populations using theoretical calculations, in which the variation in the number density was expressed in terms of molecular processes.

Phase transitions in rare earth chlorides observed by XAFS.

XAFS spectroscopy has increasingly been utilised to elucidate the nearest-neighbour structure in the condensed phases. In this paper, the XAFS spectra of NdCl3 and DyCl3 in both the solid and the liquid phases measured at the Nd and Dy L(III) absorption edges on beam line BM29 of the European Synchrotron Radiation Facility (ESRF) are presented. The Fourier transformed radial structure functions, phi(r) show that the prominent peaks corresponding to M-Cl (M: Nd or Dy) first shell contribution are shifted to shorter distances in the liquid melts as compared to those found in the corresponding solids. Similar behaviour has also been observed from other diffraction techniques in typical ionic melts such as NaCl. From the temperature dependence of the radial structure functions it is clear that the change in the M-Cl distance on melting is much larger in NdCl3 than that in DyCl3.

Experimental study of effect of rare gas admixture on temperatures of microwave-excited oxygen discharge plasma

We examined the effect of a rare gas admixture with oxygen discharge on the vibrational and rotational temperatures of the OH radical by optical emission spectroscopy (OES). We chose helium, neon, argon, krypton and xenon as admixture components with oxygen. We generated a microwave discharge oxygen plasma in a cylindrical quartz tube (26 mm i.d.) with a discharge pressure of about 1.0 Torr. The microwave frequency was 2.45 GHz and the output power was set at 600 W. To obtain the rotational temperature, we measured the band spectrum of the radiative transition A2Σ+→X2Πi of an OH radical. We compared the experimentally measured and calculated spectra to determine the actual vibrational and rotational temperatures of the generated plasma. When the mixture ratio was larger than about 80%, the vibrational and rotational temperatures markedly changed, with depended on the mixed rare gas species. The difference in temperature change is discussed from several physical viewpoints.

Internal Cation Mobilities in the Molten Binary Systems ( Y , La ) Cl3 and ( Y , Dy ) Cl3

Internal cation mobility ratios in the molten systems (Y, La)Cl 3 and (Y, Dy)Cl 3 have been measured at 1073 K by the Klemm method and the electrical conductivities of these systems have been measured by conventional ac techniques. From these studies and the data available on the densities of the pure melts, the internal mobilities, u, have been calculated; u La is greater than u y , while the ionic radius of La 3+ is greater than that of Y 3+ . On the other hand, u Y is slightly greater than u Dy , where the ionic radii are much the same and the mass of Y 3+ is much less than that of Dy 3+ . Internal mobilities of all the cations in both (Y, La)Cl 3 and (Y, Dy)Cl 3 systems decrease with increasing molar volume of the mixtures. The dominant electrically conducting cationic species are conjectured to be the nonassociated rare-earth cations.

Ion Acceleration in Arc Jet Plasma Along Open Field Lines

We experimentally study plasma parameters including the ion acoustic Mach number and the flow direction of expanding helium plasma jet flowing along open field lines. It is experimentally found that the ion Mach number increases. We discuss the mechanism of the ion acceleration. Since the ions do not rotate in electromagnets, the Hall and the swirl acceleration do not occur. We investigate the experimental results based on quasi-1-D flow model including the aerodynamic effect and the electric field. Our model describes the ion acceleration. Therefore, it is concluded that the helium ions are accelerated both by the electric field and by the increasing cross-sectional area of the supersonic flowing channel, which is determined by the magnetic flux conservation.

Titanium Oxidation by Microwave Discharge Oxygen Plasma and Relationship with Plasma Parameters

Abstract We made an experimental study on Ti oxidation by microwave discharge oxygen plasma. We treated titanium sheets with 15 × 15 × 2 mm3 in their size, and irradiated them by microwave discharge oxygen plasma with its discharge pressure several Torr. We applied XRD analysis to detect TiO2 formation after the plasma treatment, where we found only rutile pattern under the present discharge condition. To elucidate the relationship between the oxidation rate and the plasma parameters, we measured plasma parameters by probe and OES method. Measured plasma parameters were the following; electron temperature 1.8 - 5.1 eV, electron density 1.0 × 1011 - 1.0 × 1012 cm-3, vibrational temperature determined by OH radical transition 0.21 - 0.25 eV, rotational temperature determined by OH radical 0.14 - 0.15 eV, and the Ti-substrate temperature during the plasma processing 550 - 1100 K, all of which were found to be less significant to the plasma oxidation of titanium. We examined the density of oxygen atoms by actinometry measurement to be (1 - 6) × 1012 cm-3. The titanium oxidation rate was monotonically increased with the number density of oxygen atoms, whereas other plasma parameters had little correlation with the oxidation rate. The density of atomic oxygen has a significant role in plasma oxidation of titanium.

Internal Cation Mobilities in Molten (K, Dy1/3)Cl

Abstract Internal cation mobility ratios in the molten system KCl-DyCl3 have been measured at 1093 K by Klemms countercurrent electromigration method. From these, and data available on the conductivities and molar volumes of the mixtures, the internal mobilities b of both cations have been calculated. With increasing concentration of Dy, bK decreases. The decrease of bK is attributed to the tranquilization effect by Dy3+ ions which strongly interact with Cl- ions. With increasing concentration of K+ , bDy decreases; this may be attributed to the stronger association of Dy3+ with C- ions due to the enhanced charge asymmetry of the two cations neighboring to the C- ions. It could not been clarified whether a species such as [DyCl6]3- is also an electrically-conducting species in the K+ rich range.