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Drying of resorcinol-formaldehyde gels with CO2 medium |
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| Authors: | Orsolya Czakkel,Edit Szé kelyBé la Koczka,Erik GeisslerKrisztina Lá szló |
| Affiliation: | a Department of Physical Chemistry and Materials Science, Budapest University of Technology and Economics, H-1521 Budapest, Hungary b European Synchrotron Radiation Facility, 6 rue Jules Horowitz, BP 220, F-38043 Grenoble Cedex, France c Department of Chemical and Environmental Process Engineering, Budapest University of Technology and Economics, H-1521 Budapest, Hungary d Department of Inorganic and Analytical Chemistry, Budapest University of Technology and Economics, Szt. Gellért tér 4, H-1111 Budapest, Hungary e Laboratoire Interdisciplinaire de Physique, CNRS UMR 5588, Université J. Fourier de Grenoble, BP 87, 38402 St Martin d’Hères Cedex, France |
| Abstract: | The effect of using real supercritical conditions in the CO2 drying process on the structure and texture of resorcinol-formaldehyde networks is investigated by low temperature nitrogen adsorption, scanning electron microscopy and by small and wide angle X-ray scattering. If supercritical conditions are maintained throughout the whole extraction process the resulting networks exhibit much more developed porosity. The surface area of the supercritically dried gel, in excess of 500 m2/g, is more than twice that of the sample dried with liquid CO2. Pore volumes are also significantly higher in all pore classes. In the supercritical region the applied pressure strongly affects the porosity, while the effect of temperature is limited. Drying time also influences the total pore volume of the samples, but not the mesopore and micropore volumes. The volume filling character of the molecular adsorption process in this system is illustrated by the difference in surface areas measured by small angle X-ray scattering and that by nitrogen adsorption. |
| Keywords: | Supercritical drying RF gels Porosity Structure |
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