Masakatsu Misawa

Neutron-diffraction investigation of the intramolecular structure of a water molecule in the liquid phase at high temperatures

Time-of-flight neutron diffraction measurements were carried out on pure liquid water in the high-Q region and at high temperatures between 25 and 200°C. The observed data at high scattering angle ...

DENSITY DEPENDENCE OF STRUCTURE OF SUPERCRITICAL CARBON DIOXIDE ALONG AN ISOTHERM

Neutron diffraction experiments for supercritical CO2 have been carried out over a wide range of Q (0.018≤Q≤30 A−1) at ρ*=ρ/ρc=1.5, 1.2, 0.77, and 0.34 along an isotherm at 310 K (T*=T/Tc=1.02). The measurement enabled us to obtain quantitatively reliable radial distribution functions of the fluid including both short‐ranged structure and long‐ranged density fluctuation. The structure factor and radial distribution function showed the structural change from the attraction‐predominant gaslike structure to the repulsion‐predominant liquidlike one with increasing fluid density. With respect to the long‐ranged structure, almost linear Ornstein–Zernike–Debye plots were obtained for S(Q) of the fluids at all densities. A plot of correlation length against reduced density seems to have a maximum at the critical density. A ratio, α(r), of the density fluctuation produced by the correlation within r to that to the infinity presented a new aspect of the density fluctuation. Molecular dynamics simulation has also be...

Neutron and X-ray diffraction studies of PbOGa2O3 and Bi2O3Ga2O3 glasses

Abstract The structure of 50PbO·50GaO1.5 and 80BiO1.5·20GaO1.5 glasses was investigated by neutron and X-ray diffraction. Most Ga3+ ions are four-coordinated in both glasses. PbO3 trigonal pyramids and PbO4 square pyramids are present in 50PbO·50GaO1.5 glass. The stronger glass-forming ability in PbOGaO1.5 is attributed to (PbO3, PbO4)n infinite spiral chains as in crystalline PbSiO3. Bi3+ ions form BiO5 and BiO6 units in 80BiO1.5·20GaO1.5 glass as in α-Bi2O3. This glass may be constructed by (BiO5, BiO6)n layers and GaO33− chains. It is assumed that in these glasses nearly all oxygen atoms bonded to Pb2+ or Bi3+ ions are three- or four-coordinated and most oxygen atoms bonded to Ga3+ ions are three-coordinated. It is found that the structure of the present ‘non-conventional’ glasses are contrary to Zachariasens rules for glass formation.

Pulsed neutron diffraction study on lithium (I) hydration in supercooled aqueous chloride solutions

Pulsed neutron diffraction measurements have been performed on aqueous LiCl solutions (mole ratio D2O:LiCl=5) in the supercooled state (258, 213, and 173 K) and at room temperature (295 K). An isotopic substitution method with respect to Li has been used to derive the Li+‐related radial distribution function. The neutron diffraction data at all the temperatures have shown the Li–O and Li–D distances to be 2.02±0.05 and 2.61±0.05 A, respectively, and the most likely orientation of the coordinated water molecules has been found to be such that the four atoms in a Li+–D2O unit is pyramidal. It has also been found that at temperatures from 295 K down to 213 K the Li+ hydration is represented mostly by the primary hydration shell of about four coordinated water molecules, whereas at 173 K, about 40 K above the glass transition temperature, the definite second hydration shell of Li+ is formed. The obtained structural characteristics of the supercooled solutions are discussed in connection with nucleation of ice...

Molecular orientational correlation in liquid halogens

The characteristic features of structure factor Sm(Q) of liquid halogens F2, Cl2, Br2, and I2 have been discussed in terms of preferred orientational correlations introduced between the nearest neighbors. The orientational correlations estimated directly from the experimental Sm(Q)’s of these liquids are rather similar to each other and are related to a ‘‘staggered parallel’’ orientation proposed previously for liquid Br2. The characteristic features of these Sm(Q)’s are interpreted quite well by two structurally simple quantities, i.e., the ratio of intramolecular bond length to intermolecular center–center separation of correlated molecules l/Rc and that of intramolecular bond length to effective diameter of uncorrelated molecule l/σ. The characteristic features of the experimental radial distribution functions are also reproduced quite well.

A neutron scattering study of the structure of supercritical carbon dioxide

Abstract The structure factor S(Q) of supercritical carbon dioxide has been measured over a wide range of the scattering vector Q (0.018–30 A−1) using two neutron apparatuses. The measured S(Q) has been Fourier transformed into the neutron weighted radial distribution function, GN(r). This measurement enables us to analyze the short-range and long-range structures simultaneously in the supercritical fluid.

Mass-fractal clustering and power-law decay of cluster size in 1-propanol aqueous solution

Mesoscale structure of 1-propanol aqueous solutions with propanol mole fraction xp ranging from 0.1 to 0.33 has been studied by means of small angle neutron scattering (SANS) and large-scale reverse Monte Carlo (RMC) technique. Analysis of the SANS intensities in terms of a fractal model shows that the fractal dimension df of mesoscale structure of the solution is about 1.8-1.9 for water-rich solution and about 1.5 for propanol-rich solution. Percolation analysis on the RMC results reveals that the water molecules and the propanol molecules cluster, respectively, as a mass fractal, the dimension dM of which is about 2.3-2.5 for both clusters for water-rich solution. Furthermore, the distribution of the cluster size is expressed by a simple power law with an exponent tau of about 1.35-1.5 for the propanol clusters and 1.05-1.2 for the water clusters. These results imply that the current solution is characterized by polydisperse mass fractals. In fact, a theoretical relation for polydisperse system of mass fractals, df = dM(2-tau), holds well in the current solution. The characteristic change in df from 1.8-1.9 to 1.5 described above is attributed to the crossover between the water-rich regime and the propanol-rich regime. Most of the water molecules and the propanol molecules are located on the interface between clusters, and the water molecules form thin layers of about 10 A thick irrespective of 1-propanol content studied.

Small angle neutron scattering study on the salt-induced phase separation of 1-propanol aqueous solution

Small angle neutron scattering (SANS) measurements have been carried out over a wide range of Q from 0.003 to 7 A−1 on the 1-propanol-water solution with KCl and that without KCl in relation to the salt-induced reentrant phase-separation phenomena. The Q dependence of the SANS intensity for both solutions is characterized by the same fractal structure with the fractal dimension df of 1.9. The only difference between the two solutions is the value of correlation length ξ. In the solution without KCl the value of ξ is rather small, ranging from 7.4 to 6.2 A depending on temperature, while in the solution with KCl it becomes very large, from 48 to 355 A or more depending on temperature, and diverges toward the phase-separation temperatures in a similar way for both the upper and lower one-phase regions. No significant differences have been found on the growing structure of fluctuation in the upper and lower one-phase regions.

Neutron diffraction and solid-state MAS-NMR studies of the structure of Y-AI-Si-O-N oxynitride glasses

Abstract Neutron diffraction and magic angle spinning (MAS) 27Al and 29Si NMR have been applied to study the local structure of glasses in the system Y-Al-Si-O with and without addition of AlN. 27Al MAS NMR indicated that in the Y-Al-Si-O-N oxynitride glass there is no Al-N bonding and aluminium atoms occupy various sites within the glass structure. The first peak of the radial distribution function curves obtained by neutron diffraction was deconvoluted into four peaks which are attributable to Si-O, Si-N(Al-O(4)), Al-O(5) and Al-O(6) pairs and the coordination numbers of Si, N, Al and Y were estimated. The glass network is assumed to consist mainly of corner-sharing AlO4 tetrahedra and SiO3N tetrahedra. 86% of N atoms are three-coordinated and 14% of N atoms are two-coordinated in the present oxynitride glass.

Partial Structure Factor of Amorphous Cu0.57Zr0.43 Alloy Determined by TOF Pulsed Neutron Diffraction

The partial structure factors S CuCu ( Q ), S CuZr ( Q ) and S ZrZr ( Q ) are determined consistently from the three total structure factors S ( Q ) for amorphous Cu 0.57 Zr 0.43 alloys with natural Cu, isotope Cu 63 and Cu 65 , which were observed by means of TOF pulsed neutron diffraction. The reduced partial radial distribution functions G i j ( r ) are also obtained by Fourier transforms of S i j ( Q ). The first peaks of G CuCu ( r ), G CuZr ( r ) and G ZrZr ( r ) appear at r =2.65, 2.80 and 3.15 A, respectively. The second peaks of both S i j ( Q ) and G i j ( r ) split into two subpeaks. This is interpreted as a consequence of tetrahedral close packing in amorphous alloys.