2 research outputs found
Influence of Gas for Thermal Treatment on Hydrogen Permeation in V–Ni Alloy Membranes
Hydrogen separation is an important step for the utilization
of
hydrogen energy. Metallic alloys, such as vanadium–nickel,
are potential hydrogen separation materials. Due to the strong propensity
of vanadium to form oxides and hydrides, vanadium alloy has a lower
hydrogen permeability, and it is difficult to maintain the permeability
over time. Therefore, special preparation processes such as Pd coating
have been suggested for hydrogen separation vanadium-based membranes.
However, aside from the prohibitive price of palladium, the interdiffusion
of palladium and vanadium makes the coated membrane inviable to be
used at a high temperature. Thermal treatment with inert gas was investigated
in this study to assess the applicability of the vanadium alloy without
palladium coating for hydrogen separation and clarify the mechanism
behind the thermal treatment. Argon is inert with vanadium and displayed
permeability recovery after 43 h thermal treatment, but the permeability
declined under certain conditions. In contrast, nitrogen is known
to interact with vanadium and the hydrogen permeability was maintained
at a level lower than the test with argon. Given that nitrogen can
compete with hydrogen for the active sites on vanadium, nitrogen might
hinder hydrogen adsorption and hydride formation, whereas argon reduced
the partial pressure of hydrogen during the thermal treatment, enhancing
the driving force of hydrogen desorption. In the X-ray diffraction
spectrum, vanadium hydrides and oxides were confirmed after hydrogen
permeation and thermal treatment. In the X-ray photoelectron spectroscopy
data, oxygen was a dominant element due to vanadium oxides and adsorbed
nitrogen was also observed. According to binding energy shifts of
nitrogen, nitrogen used for thermal treatment might substitute or
compete for active sites with adsorbed nitrogen and hydrogen, existing
in vanadium lattice. Although thermal treatment can be used to recover
hydrogen permeability, the alloy cannot be recovered as hydrogen-free.
However, results demonstrate the potential of thermal treatment to
complement an uncoated vanadium alloy for a hydrogen separation membrane
Interaction of Silica Nanoparticles with a Flat Silica Surface through Neutron Reflectometry
Neutron reflectometry (NR) was employed to study the
interaction
of nanosized silica particles with a flat silica surface in aqueous
solutions. Unlike other experimental tools that are used to study
surface interactions, NR can provide information on the particle density
profile in the solution near the interface. Two types of silica particles
(25 and 100 nm) were suspended in aqueous solutions of varying ionic
strength. Theoretical calculations of the surface interaction potential
between a particle and a flat silica surface using the Derjaguin–Landau–Verwey–Overbeek
(DLVO) theory were compared to the experimental data. The theory predicts
that the potential energy is highly dependent on the ionic strength.
In high ionic strength solutions, NR reveals a high concentration
of particles near the flat silica surface. Under the same conditions,
theoretical calculations show an attractive force between a particle
and a flat surface. For low ionic strength solutions, the particle
concentration near the surface obtained from NR is the same as the
bulk concentration, while depletion of particles near the surface
is expected because of the repulsion predicted by the DLVO theory