BASIC CONCEPTS AND AN OVERVIEW - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 62

tion temperature, which was supposed to be due to shrinkage during carbonization
[1, 2, 54, 55].
1.1.10.7.2 MACROPOROUS CARBONS (CARBON FOAMS)
Carbon foams were prepared from mesophase pitch through either blowing or
pressure release of molten pitches followed by stabilization in air. Because the
foam with a high thermal conductivity attracted attention for a potential filler ma-
terial of some composites, the preparation of a large sized carbon foam with high
thermal conductivity from mesophase pitch by a new and less time consuming
process was extensively studied. The graphitized foams have the bulk density of
0.2-0.6 gcm −3 , with an average pore size of either 275-350 micrometers or 60-90
micrometers and relatively high graphitization degree.
1.1.10.7.3 INTERCALATION
Intercalation of various species into graphite gallery can be considered to be the
chemical adsorption into intrinsic pores, which are flexible and two-dimensional
slit-shaped micropores. These intercalation phenomena are one of characteristics
of carbon materials in graphite family. In addition, intercalation can be under-
stood as a new process to create extrinsic pores in the compounds, of which the
size is controllable by the size of intercalates. In graphite intercalation compounds
(GICs) of alkali metals with 2D structure, for example, nanospaces are formed
surrounded by alkali metal ions and graphite layer planes. As an example, ar-
rangement of Cs + ions in graphite gallery. In this compound, the space with the
size of approximately 0.311 × 0.266 nm can accept the third component. Chang-
ing the alkali metal ions to K (ion radius of 0.133 nm) and Rb (0.148 nm) from
Cs + (0.169 nm), the size of the space for the third component changes [1, 2].
1.1.10.7.4 EXFOLIATION
Exfoliated graphite has been produced as a raw material for flexible graphite
sheets in a huge amount in the world. Usually it is produced through rapid heat-
ing of residue compounds of natural graphite flakes with sulfuric acid up to a
high temperature as 1000°C. It consists of fragile worm-like particles, which are
formed by exfoliating preferentially along the normal to the basal plane of graph-
ite. There are at least three kinds of pores in exfoliated graphite. Large pores are
formed mainly by the complicated entanglement of worm-like particles during
abrupt exfoliation of each graphite flakes and so they are flexible interparticle
macropores. In addition, crevice-like pores on the surface of worm-like particles
and pores inside the particles are formed,respectively. In order to evaluate the
pores, which are rigid intraparticle, pores, a technique to prepare fractured cross-
section of worm-like particle had to be developed and various pore structure pa-
rameters were determined with the aid of image processing technique.