We report experimental data on the mechanical stability of the silica mesoporous material MCM-41. Using X-ray diffraction and nitrogen adsorption we show that the ordered mesoporous structure of MCM-41 can be affected considerably by mechanical compression at pressures as low as 86 MPa and essentially destroyed at 224 MPa.
Permanent hysteresis, meaning the hysteresis which is stable with regard to the change in the process rate, is known to occur in capillary condensation/evaporation of wetting fluid and intrusion/extrusion of nonwetting liquid in porous solids. No satisfactory thermodynamic description of the permanent hysteresis in these processes exists at present, despite their use in thermodynamic interface characterization of dispersed systems. Also, in the case of lyophobic systems, no direct determination of total energetic exchange of the system exhibiting hysteresis has been reported. Considering quasi-isothermal irreversible processes in capillary lyophobic systems, we obtained expressions of energy and entropy balances which relate equilibrium physical characteristics of the system, energetic exchange, and internal entropy production. This provides a strict base for a modelless thermodynamic method of evaluation of the cumulative interface areas and entropy of the change of interface areas and then the pore volume distribution and surface fractal dimension of porous solid. For the first time, along with p-V measurements, direct determinations of heats of high-pressure intrusion and extrusion of water in pores of hydrophobized silica gel have been undertaken. Analysis of these data shows validity of the developed approach.
The surface and pore structure properties of the C60 and C60/C70 fullerene powders were studied by means of
scanning electron microscopy, helium pycnometry, and 77.4 K nitrogen and argon adsorption. The pore structure
of fullerene powders is macroporous and consists mainly of the voids between the fullerene aggregates. In
the major part of the adsorption monolayer, both nitrogen and argon interactions with fullerenes are weaker
than with graphite, possibly because of the reduction of the gas molecule−mirror image effect in the case of
fullerenes. In Henry's law limit, however, nitrogen and argon adsorption on fullerenes is quantitatively similar
to that on graphite because of the adsorption potential enhancement in the spaces between the surface fullerene
molecules. In the multilayer regime, nitrogen adsorption on both fullerenes becomes similar to that on graphite.
Both fullerenes behave similarly with respect to the adsorption of the studied gases.
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