Correlation between Microscopic Structure and Chemical Reaction in Low-density Supercritical Water

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(1)High-temperature and high-pressure solution sample cells for XAFS, small-angle X-ray and neutron scattering have been constructed. Maximum pressure and temperature used for the cells are 50 MPa and 400 ﾟC.(2)XAFS measurements on 0.1 M aqueous Co(N03)2 solution were made at 25ﾟC(0.1 MPa), 250ﾟC(30 MPa), and 400ﾟC(35 MPa). It has been found that the hydration number of Co^<2+> decreases from 6 at 25ﾟC to 4 at 400ﾟC, the Co-H_2 distance being 2.06-2.08 A.(3)The structure of methanol at ambient (25ﾟC), subcritical (202ﾟC), and supercritical(253ﾟC)temperatures has been investIgated by neutron diffraction with hydroxyl H/D) substitution and Empiricat Parameter Structure Refinement methods. It has been found that methanol molecules are arranged as chain-like by hydrogen bonding and that clusters of 5-6 methanol molecules are formed at the supercritical temperature and are broken down with decreasing density.(4)X-ray diffraction measurements on a methanol-water binary solution (methanol mole fraction is 0.3) were made over a temperature range 25-200ﾟC.It has been found that hydrogen bonds at 2.9 A are largely broken down with increasing non-hydrogen bonds at 3.5 A.(5)The orientational correlation function on Cl hydration in supercritical water has been derived by neutron diffraction on a 3 m LiCl solution in D_2 with ^<35>C/^<37>C substitution, EPSR, and spherical harmonic expansion methods. It has been found that all water molecules around Cl remain in the first coordination shell, but are randomly oriented toward Cl.