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The adsorption of nitrogen in a collection of spheres that touch or merge in a sintering-like manner is modeled using a Derjaguin-Broeckhof-de Boer approach. The proposed model accounts for both positive curvature effects and for capillary condensation at the contact between two spheres. A methodology is proposed to fit the P/P(0)>0.4 adsorption region with the coordination number of the spheres as the only adjustable parameter. The use of the model is illustrated on a series of silica aerogels. The suitability of various standard isotherms needed for the modeling is also discussed. 相似文献
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Gommes CJ 《Langmuir : the ACS journal of surfaces and colloids》2012,28(11):5101-5115
A Derjaguin-Broekhoff-de Boer analysis of adsorption and desorption in SBA-15 mesoporous silica is presented, using realistic geometrical models that account for the pore corrugation in these materials. The model parameters are derived from independent electron tomography and small-angle scattering characterization. A geometrical characteristic of the pore that is found to be important for adsorption is the corrugation length, l(C), which describes the longitudinal size of the geometrical defects along a given pore. Capillary bridges are possible only for large values of l(C). The results are explained in terms of two spinodal and two equilibrium pressures, characterizing the wide and the narrow sections of the pores. Simplified analytical expressions are obtained, which provide necessary conditions for bridge formation and for cavitation in terms of the radii of the narrow and wide sections of the pores, as well as of l(C). Quite generally, the results show that the deviation of the pore shape from that of ideal cylinders is key to understanding adsorption and desorption in corrugated mesopores, notably in SBA-15. 相似文献
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The present paper shows how a standard volumetric adsorption device can be used to measure solvent desorption isotherms on
gels. As gels are very soft materials, they shrink significantly during the measurement, and the data have to be analyzed
in terms of the mechanical properties of the gel’s skeleton. Methanol desorption isotherms are measured on a series of silica
gels, and the results are compared with independent characterizations, notably beam bending. 相似文献
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Cédric J. Gommes Silvia Blacher Jean-Paul Pirard George W. Scherer 《Journal of Sol-Gel Science and Technology》2007,44(3):211-218
The effect of evaporative drying on the pore size of two series of hybrid silica gels is investigated by combining beam bending
on the gels and mercury porosimetry on the aerogels and xerogels with transmission electron microscopy on the xerogels. It
is shown that the shrinkage of the pores during drying is different in the two series: in one series the pores shrink proportionally
to their volume, in the other the pores collapse until they all reach the same size. The experimental data enable us to discuss
the relation between these two different behaviours and the different morphology of the two series of gels. 相似文献
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The technique of ferromagnetic resonance at 23 GHz has been used to determine the first three anisotropy constants of pure Ni down to 4.2K. A temperature and orientation dependent linewidth has also been observed. 相似文献