Heidy Visbal

Controllable hydrogen release via aluminum powder corrosion in calcium hydroxide solutions

Abstract Mechanism of aluminum powder corrosion in calcium hydroxide solutions was investigated via various analyses of residues after its hydrolysis reaction and pH change of the solutions to control the release of hydrogen gas. It was revealed that the reaction with a release of hydrogen gas consisted of katoite formation and hydration of aluminum. The katoite formation, which is progressed by the reaction among calcium ion, aluminum hydroxide anion (Al(OH)4−), and water molecules at the first step, is important for the promotion of aluminum corrosion and moderate release of hydrogen gas.

Surface analysis of three aluminum foils and relation to hydrogen generation capability

We have successfully generated hydrogen using aluminum foil instead of aluminum powder from the perspective of improving safety. We analyzed the surface states of three aluminum foils and correlated their surface properties with hydrogen generation capability. The surfaces of the foils were analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy, and atomic force microscopy. Hydrogen generation was performed by adding Ca(OH)2 solution to the aluminum foil in water. The TOF-SIMS results showed that the Al foils have Al2O3-, AlO2-, (OH)2AlO-, (Al2O3)OH-, and (Al2O3)AlO2- and related species on their surfaces. The amount of these species on the surface of an Al foil is linearly correlated with the hydrogen generation reaction rate.

Role of partial molar enthalpy of oxides on Soret effect in high-temperature CaO–SiO 2 melts

The Soret effect or thermodiffusion is the temperature-gradient driven diffusion in a multicomponent system. Two important conclusions have been obtained for the Soret effect in multicomponent silicate melts: first, the SiO2 component concentrates in the hot region; and second, heavier isotopes concentrate in the cold region more than lighter isotopes. For the second point, the isotope fractionation can be explained by the classical mechanical collisions between pairs of particles. However, as for the first point, no physical model has been reported to answer why the SiO2 component concentrates in the hot region. We try to address this issue by simulating the composition dependence of the Soret effect in CaO–SiO2 melts with nonequilibrium molecular dynamics and determining through a comparison of the results with those calculated from the Kempers model that partial molar enthalpy is one of the dominant factors in this phenomenon.