II International Symposium on Carbon for Catalysis ABSTRACTS

KL-6
The second part is estimating the role of the surface tension of the pore walls. The
difficulty of such estimation originates from the difference of the mechanical and
thermodynamic definitions of surface tension for solids (in particular, the mechanical surface
tension does not coincide with surface free energy). It is shown that the mechanical surface
tension contributes to the initial contraction of a microporous catalyst in vacuum, but cannot
cause an additional contraction with a sorbate since physical adsorption leads to a decrease of
surface tension, while chemisorption does not influence surface tension at all. The
introduction of the internal pressure tensor in a pore and of the surface tension of the pore
walls determines a force applied to the bulk phase of a porous body. The resulting normal
stress E N
in the solid phase is
E () c = 2 γ c − p () c , (2)
N
N
where c is the mean curvature of the pore wall, γ is the mechanical surface tension, and
p
N
is
the normal (radial) component of the pressure tensor inside the pore. The knowledge of stress
E N
permits passing to the calculation of strain. The third part of theory presented is devoted
to such calculations within the frames of the theory of elasticity. The latter is quite applicable
to this case because the mechanical effects under consideration are sufficiently small to
assume the elastic behavior of a solid. Ready solutions were taken from the theory of
elasticity to apply the problems of strain of a hollow tube and of a hollow ball to the cases of a
cylindrical pore and a spherical pore, respectively. The result is expressed as the relative
change in the volume and linear dimensions of a porous body. Examples of numerical
estimations are given for microporous bodies in vacuum.
The work has been done under the financial support of the program “Leading Scientific
Schools of Russian Federation”.
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