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- Author or Editor: J. Rouquerol x
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The adsorption of argon, oxygen, nitrogen and carbon monoxide at 77 K on crystalline zirconia and microporous zirconia gels has been studied by adsorption volumetry and isothermal microcalorimetry.
Abstract
The reduction of UO2F2 by dry H2 was studied by Controlled Rate EGA, with a special set-up operating under a gas flow under atmospheric pressure. At the constant transformation rate selected, this reduction apparently takes place in one main step, around 450C (for a total duration of 100 h), followed by a small exothermic step. The final product is a stoichiometric, well crystallized UO2. XRD analysis shows the occurrence of two successive intermediates of which one has a structure close to that of UO2, but with interstitial fluorine atoms.
Abstract
Then-alkanes of different lengths were preadsorbed to selectively block part of the micropores of a MFI-type zeolite, Silicalite-I. The porosity available to argon and nitrogen was then studied by quasi-equilibrium adsorption microcalorimetry and volumetry at 77K and compared to what was found for the bare zeolite. Indeed, although partial adsorption ofn-alkanes does not alter the value of the differential enthalpies of adsorption for both argon and nitrogen, then-butane preadsorption diminishes the adsorption capacity by inducing inaccessible volumes in the micropore network. Moreover, the microcalorimetric experiments clearly show thatn-butane is not evenly distributed in the zeolite channel network while the longern-alkanes used are.
Abstract
The adsorption of the paraquat molecule on silica, kaolinite, illite and montmorillonite was studied with regard to both the determination of adsorption isotherms and the microcalorimetric measurement of adsorption enthalpies. Surface concentration at saturation can be related to the neutralization of the surface charge. Part of the observed variation in adsorption enthalpies from one mineral to another can be attributed to the degree of fitting of the adsorptive molecule to the spatial repartition of surface charges. A particularly interesting system is that involving montmorillonite, where there is evidence of the possibility of neutralization, by the same paraquat molecule, of two sites relating to different platelets.
Abstract
The synthesis of new ordered mesoporous adsorbents, specifically of the MCM-41 type, involves a step of thermal elimination of the template (a surfactant) where CRTA is shown to provide a 'soft chemistry' route. Once the mesoporous (i.e. 2 to 50 nm pore width) material is obtained, the pore size is determined by thermoporometry, a convenient application for low temperature DSC. Finally, the hydrophobic - hydrophilic properties of the pore walls are explored by immersion microcalorimetry in water.
The adsorption of argon and nitrogen on a series of MFI-type zeolites (silicalite-I (Si/Al>1000) and HZSM-5 (16<Si/Al<120)) was studied by isothermal microcalorimetry, volumetry and neutron diffraction.
Abstract
Emanation thermal analysis (ETA) was used for thermal characterization of microstructure changes taking place during heating of synthetic gibbsite sample in argon in the range of 25–1200C. Microstructure development and the increase of the surface area under in-situ conditions of the sample heating were characterized. The increase of the radon release rate from 130–330C monitored the increase of the surface area due to the dehydration of Al(OH)3. During heating of the sample in the range 450–1080C the ETA results characterized the annealing of surface and near surface structure irregularities of intermediate products of gibbsite heat treatment. The mathematical model for the evaluation of the ETA experimental results was proposed. From the comparison of the experimental ETA results with the model curves it followed that the model is suitable for the quantitative characterization of microstructure changes taking place on heating of gibbsite sample.
