Titanium oxide¯lms were deposited on Si and quartz substrates by RF magnetron sputtering of titanium target under various oxygen partial pressures. The¯lms were annealed in air at di®erent temperatures and the in°uence of annealing temperature on the structural and optical properties was studied. The XPS studies revealed that the¯lms formed at oxygen partial pressure of 2 Â 10 À2 Pa were nearly stoichiometric. The as-deposited¯lms were amorphous, thē lms annealed at 573 K were anatase, while those annealed at 973 K were mixed anatase and rutile phases of TiO 2 . The as-deposited¯lms showed an optical bandgap of 3.32 eV while those annealed at 973 K was 3.19 eV.
The kinetics of hydrogenation/reduction
of uranium [U(VI)] has
been investigated using a platinum catalyst loaded on silica substrates
in a bubble column reactor at atmospheric pressure and room temperature.
Effects of catalyst loading, hydrogen flow rate, and concentrations
of nitric acid and hydrazine have been investigated. Several kinetic
models are derived based on the Langmuir–Hinshelwood mechanism
and each of them are evaluated. The experimental results indicate
that the surface reaction between dissolved hydrogen and adsorbed
reactants on the catalyst surface is the rate controlling step in
the hydrogenation of uranyl ion. To test the applicability of the
developed rate expression, the mass balance equations for uranium,
nitric acid, and hydrogen around the bubble reactor have been solved
numerically. The comparison of experimental and predicted results
showed a reasonably good agreement.
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