Characterization of the State of Two-Dimensionally Condensed Water on Hydroxylated Chromium(III) Oxide Surface through FT-IR, Quasielastic Neutron Scattering, and Dielectric Relaxation Measurements

Abstract

The dynamic properties of water molecules adsorbed on the hydroxylated chromium(III) oxide surface, whose two-dimensional critical temperature was 303 K, were investigated at around the two-dimensional critical temperature by FT-IR, quasielastic neutron scattering, and dielectric relaxation techniques. The Cr 2 O 3 sample covered with monolayer water gives an IR band having a broad nature at ∼3400 cm -1 , due to the mutual hydrogen bonding among the adsorbed water molecules. The quasielastic neutron scattering data have revealed that the motion of the adsorbed water molecules changes across the two-dimensional critical temperature, ranging from the motion of the supercritical fluid to that of a solidified phase with decreasing temperature. The dielectric spectra observed at 298 K and at the coverage of 1.1 monolayers have been interpreted in terms of the presence of two relaxations due to the interfacial and orientational polarizations. The characteristic frequency of the relaxation for the latter polarization was estimated to be ca. 300 Hz. It is concluded from these findings that the two-dimensionally condensed waters adopt the mutually hydrogen-bonded solid state having a commensurate structure with the hydroxylated (001) Cr 2 O 3 surface below the two-dimensional critical temperature of this system. In addition, the interfacial polarization was explained in terms of a hopping model of protons of the adsorbed molecules. The behavior of conductivity arising from this proton hopping also indicates the morphology of the two-dimensionally condensed water below the monolayer coverage: the small clusters of water are formed on the Cr 2 O 3 surface.

Dynamics and Structure of Hydration Water on Rutile and Cassiterite Nanopowders Studied by Quasielastic Neutron Scattering and Molecular Dynamics Simulations

“…Sample Preparation and Characterization. Rutile (RTiO 2 ) nanocrystals were synthesized by thermohydrolysis of titanium chloride (TiCl 4 , 99.9%, Aldrich) under acidic conditions. A clear solution was first prepared by dropwise addition of 11.0 mL of pure liquid TiCl 4 into 100 mL of 1.0 M HCl aqueous solution under vigorous stirring at ice-cooled temperature.…”

“…A clear solution was first prepared by dropwise addition of 11.0 mL of pure liquid TiCl 4 into 100 mL of 1.0 M HCl aqueous solution under vigorous stirring at ice-cooled temperature. After storage at 4°C for 12 h, the TiCl 4 solution was diluted with water to 0.2 M of TiCl 4 and then kept at 85°C for 12 h. Upon completion of the reaction, the white colloid was transferred into dialysis tubing (SnakeSkin, molecular weight cutoff at 10000, Pierce Chemical Co.) and dialyzed against deionized water (resistivity g18.0 MΩ‚cm) until minimum of conductivity was reached for removal of all free ions. Then the purified colloid was separated by centrifuge and redispersed in water.…”

“…A total of 11.7 mL of pure liquid SnCl 4 was first added to 100 mL of 10 -3 M HCl in aqueous solution. Then the solution was diluted with water to 0.1 M of SnCl 4 and transferred into a Teflon container inside a steel autoclave. The SnCl 4 solution was kept at 150°C for 16 h for the hydrolysis reaction.…”

“…Then the solution was diluted with water to 0.1 M of SnCl 4 and transferred into a Teflon container inside a steel autoclave. The SnCl 4 solution was kept at 150°C for 16 h for the hydrolysis reaction. The resulting white-gray SnO 2 colloid was purified by dialysis, redispersed in pure water by sonication, and then kept at 150°C for an additional 16 h before freezedrying.…”

Effects of water vapor on protectiveness of Cr2O3 scale at 1073 K

“…The experimental 2D phase diagram was described by the simulation, which gave the 2D critical temperature of T=319 K. They proposed structure of the monolayer of water below the 2D critical temperature is composed of a net of many hexagonal water molecules registered on the hexagonal structure of the hydroxylated surface. An analysis of Cr 2 O 3 -H 2 O system using FT-IR and neutron scattering were done by Kuroda [4] and Morishige et al [5]. In this system, the relaxation frequency for the dipolar relaxation of adsorbed water was found.…”