Preparation of silica-based microporous inorganic gas separation membranes

Fully inorganic silica-based membranes have been prepared using sol-gel procedures starting from sodium silicate solutions. An asymmetric membrane structure is obtained by multiple deposition of colloidal silica sols onto commercial ceramic supports. The microporous structure of the silica which forms the active top layer remains stable up to 873 K and is characterised by a mean pore diameter of 1.6 nm, a narrow pore size distribution and a porosity of 35%. The continuous silica top layer of the membrane was analysed by SEM and checked by gas permeation measurements. The permeabilities of CH4, N2 and CO2 were measured for membranes deposited onto zirconia supports as a function of temperature. The preliminary experimental results indicate reproducible and relatively high fluxes as well as a transport mechanism which basically follows Knudsen flow with contributions from surface and microporous diffusion

Study of partial occupancies and Jahn-Teller distortions in (Na,□)5[MnO2]13 by XRPD Rietveld and electron diffraction dynamical refinements

4nononenoneMugnaioli E., Gemmi M., Merlini M., Gregorkiewitz M.Mugnaioli, E.; Gemmi, M.; Merlini, M.; Gregorkiewitz, M

Hydrogen positions and thermal expansion in lizardite 1T from Elba by Rietveld powder neutron diffraction.

The structure of lizardite-l T from Monte Fico, Elba, was refined in space group P31m using neutron diffraction data, measured at 8, 150, and 294 K, and full-profile Rietveld refinement techniques. The lattice parameters at 8 K [a = 5.3267(2), c = 7.2539(6) A], 150 K [a = 5.3260(2), c = 7.2574(6) A], and 294 K [a = 5.3332(2), c = 7.2718(6) A] show nonlinear expansion, with nearly all volume change above 150 K. H positions were precisely refined at 8 K. The inner H4 atom deviates from the idealized O,O,zpositions and is disordered over three symmetry-related positions 0.24 A away from the ternary axis. The outer H3 atom location is consistent with the previous single-crystal X-ray structure refinement. On the basis of the present thermal expansion data and previous compressibility measurements, the following equation of state for lizardite-I T is proposed: Vp,T = Vo[1 + 32.8 x 10-6(T - 294) - 15.5 x 10⁻⁴(P - 0.001)]. Accordingly, the constant volume condition requires geothermal gradients on the order of 15 °C/km

Hydrogen positions and thermal expansion in lizardite-1T from Elba: A low-temperature study using Rietveld refinement of neutron diffraction data

The structure of lizardite-l T from Monte Fico, Elba, was refined in space group P31m using neutron diffraction data, measured at 8, 150, and 294 K, and full-profile Rietveld refinement techniques. The lattice parameters at 8 K [a = 5.3267(2), c = 7.2539(6) A], 150 K [a = 5.3260(2), c = 7.2574(6) A], and 294 K [a = 5.3332(2), c = 7.2718(6) A] show nonlinear expansion, with nearly all volume change above 150 K. H positions were precisely refined at 8 K. The inner H4 atom deviates from the idealized O,O,zpositions and is disordered over three symmetry-related positions 0.24 A away from the ternary axis. The outer H3 atom location is consistent with the previous single-crystal X-ray structure refinement. On the basis of the present thermal expansion data and previous compressibility measurements, the following equation of state for lizardite-I T is proposed: Vp,T = Vo[1 + 32.8 x 10-6(T - 294) - 15.5 x 10⁻⁴(P - 0.001)]. Accordingly, the constant volume condition requires geothermal gradients on the order of 15 °C/km

Structural Assessment of the Electrochemical Performance of LixCoO2 Membrane Electrodes by X-Ray Diffraction and Absorption Refinements

LixCoO 2 samples with different nominal load x were prepared submitting HT-LiCoO2 membrane electrodes to electrochemical polarisation, followed by aging in open circuit conditions. Care was taken to obtain samples for both positive and negative overcharge beyond the canonical regime (0.6 _Co substitution. Results from Co-K edge X-ray absorption spectroscopy for the samples with x = 0.37, 0.89, 1 and 1.43 show a clear shift of the absorption maximum with the oxidation state of Co and support the conclusions from Rietveld refinement. GNXAS refinement of EXAFS spectra for the samples with x = 0.37 and 1 suggest that cation disordering may occur also for deep lithium deintercalation (positive overcharge), a fact which was not detectable from diffraction data