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Aerogels are highly porous materials that are produced via sol-gel processing and supercritical drying. Titanium dioxide aerogels were prepared using a variety of sol composition from the system Ti(OC3H7)4 / H2O/ EtOH / HNO3. The morphology of titanium dioxide aerogel was characterized by krypton adsorption, X-ray diffraction, scanning and transmission electron microscopies. The surface area, pore volume and pore size distribution of TiO2 aerogels
Read moreThe relation between the critical value V*; of the barrier layer voltage and the mean coordination number of the oxygen in the first coordination sphere around the aluminium atom was investigated in order to illustrate the transition from conventional to hard anodization. The modification from open to closed structure is very sharp in the neighbourhood of V*;.
Read moreFourier analysis of EXAFS data, a self-contained fortran program-package has been elaborated.
Read moreThe effects of the thickness of thin electrodeposited palladium layers on the kinetics of hydrogen desorption processes are reported. Measurements have been performed with a piezoelectric quartz crystal microbalance under dynamic conditions, at a constant temperature of 61.1 ± 0.05 °C, and three different hydrogen-equilibrium pressures (α-phase region). From the kinetic analysis of desorption data, the desorption rate constants for the first-order
Read moreThe influence of crystalline microstructure upon the apparent diffusion coefficient of hydrogen in Pd samples are reported. The apparent diffusion coefficient was measured by the galvanostatic permeation method (at 20°C), while the structure was characterized by X-ray diffraction measurements. Pd membrane electrodes of different thicknesses, l = 5 × 10−3cm and l = 10−2cm, were used. The structure of Pd membrane electrodes was changed by successive
Read moreThe hydrogenation of the alloy of composition CaMg1.8Ni0.5 containing CaMg2 and MgNi2 shows fast activation kinetics. The Mg2Ni phase is observed in the dehydrided samples. The three plateaus on the hydrogen desorption isotherms correspond to the most stable magnesium hydrides observed up to now in Mg-alloy (ΔH = 20–24 kcal/mol H2). The effects of Ca additions on the hydrogen storage capacity and desorption rates of some Mg-rich alloys have been
Read moreThe pressure-composition isotherms for the systems LaNi5-H2 and LaNi5-D2 have been measured both for absorption and for desorption in the temperature range - 10 to +65 °C. The ratio of the plateau pressures, View the MathML source, is r < 1 at high temperatures, and becomes r > 1 at lower temperatures, depending on the thermal treatment of the sample. From the plateau pressures at a constant hydrogen (or deuterium) concentration in LaNi5 (3D or
Read moreThe substitution of chromium for vanadium in ZrV1.5-x Cr x Ni 1.5 leads to a cubic C15 phase as the main phase with a low content of the secondary phase Zr7Ni10. The lattice parameters suggest a complex redistribution of V, Ni or Cr between the B and A sites of the Laves phase AB2, which does not depend only on the Cr content. The pressure-composition isotherms show sloping plateaux, alloy hydrogen contents between 3.35 and 4.25 H/mol and desorption
Read moreEuropium activated yttrium aluminate (YAG:Eu) phosphors were synthesized using urea by wet chemical synthesis route. The luminescent behavior and the microstructural changes are monitored, depending on the amount of europium. The luminescent spectra of YAG:Eu phosphors possess four major emission bands in the range of 570–700 nm with maxima situated at 592 nm 598 nm, 611 nm and 631 nm. The intensity ratio between the 611 nm band as red component
Read moreThin PbS films were chemically deposited on glass from alkaline baths containing lead nitrate, thiourea and different additions, such as hydroxylamine hydrochloride, triethanolamine or H2O2. The structural, optical and photoelectrical properties of these films were studied. The main characteristic of films as thick as 0.12–0.54 μm is the photosensitivity. This parameter is influenced by many factors such as film thickness, grain and crystallite
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