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Gregg S.J., Sing K.S.W. Adsorption, Surface Area and Porosity (2ed., AP, 1982)(T)(ISBN 0123009561)(313s).djvu |
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Size 3.2Mb Date Nov 13, 2004 |
were substantially confirmed by Havard and Wilson47 in their detailed
study on Gasil 1, one of the standard materials used in the surface area
project referred to in Chapter 2 (p...
Figure 3.20, which refers to graphs from
compacts of silica powder prepared at successively higher pressures,
provides an illustration...
The time is perhaps not yet ripe, however, for introducing this kind of
correction into calculations of pore size distribution: the analyses, whether
based on classical thermodynamics or statistical mechanics are being
applied to systems containing relatively small numbers of molecules where,
as stressed by Everett and Haynes,21 the properties of matter must exhibit
wide fluctuations...
Now the maximum tension that a liquid can withstand is equal to
its tensile strength t0: consequently there will be a minimum value {p/p°)i,,
say, compatible with the continued existence of capillary-condensed liquid,
and given by
/1/ \
to C.61)
This minimum value should be constant for a given adsorptive at a given
temperature, irrespective of the nature of the adsorbent...
Meanwhile, as a
valuable working hypothesis, it leads to an important implication for pore
size calculations: the Kelvin equation can give no information as to the
presence or absence of pores having a value of rm below 10 to 15 A (the exact
value depending on the particular adsorbate and the temperature)...
In formulating an explanation of this enhanced adsorption, there are
several features to be accounted for: the increase in adsorption occurs
without hysteresis; the amount of adsorbate involved is relatively small; the
Kelvin revalues are also small (e.g...
This is largely a reflection of the widespread use of nitrogen for
surface area determination, which has meant that both the pore size
distribution and the specific surface can be derived from the same isotherm...
The number
of published isotherms of vapours such as benzene, carbon tetrachloride or
the lower alkanes, or even such simple inorganic substances as carbon
dioxide, on a reasonable number of well-defined non-porous adsorbents, is
very small...
The uncertainty arising from this cause is
considerable, since the curve of ln(p°/p) 's very steep in this region (cf...
In addition, the
average of the adsorption and desorption values is always below the BET
area...
Mesoporous solids: the Type IV isotherm
175
Section 3.7, the gas adsorption method breaks down for practical reasons...
I mN m ' = 1 dyn cm"
13 Mesoporous solids: the Type IV isotherm 177
¦¦since 1945 for the surface tension in vacuo...
Thus
in mercury porosimetry the cumulative pore volume c(Hg) decreases as rp
increases, whereas in gas adsorption ?(&T) of course increases with
increasing rp...
{plp")w is 0-98 for rj, = 1000 A, and 0-998 for r" = 10000 A) and is beyond
the scope of the benzene measurements...
Pinote and co-
workers,102 for example, studying a series of graphitized cokes, found that
the volume penetrated by mercury at 1000 atm actually exceeded the volume
accessible to helium, showing that the mercury had opened up the structure...
When the pores are full, the next increment of liquid
forms a film on the outside of the particles, which by virtue of its surface tension draws
the particles together...
Their pore
structure, as revealed by both nitrogen adsorption and by mercury
porosimetry, varied markedly according to the particular alcohol and the
concentration of the solution...
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