Biomedical Engineering Reference
In-Depth Information
presented earlier in Refs. [27, 28] by the authors of this review. It
should be noted that, unlike fullerenes, astralene is a fairly new
material. The astralene, a polyhedral multi-layer fulleroid-type
carbon nanostructure, is produced by means of the well-known
arc-discharge method using graphite electrodes in rare gas
atmosphere and special conditions of the plasma process, with
subsequent separation and oxidative treatment of the cathode
deposit [29]. The choice of astralene as object of specific research
is explained considering the increasing interest given to the various
new materials related to fullerenes, such as near-spherical carbon
nanoshells [30], carbon nanocapsules [31], or carbon onions [32],
which consist of concentric multi-layer fullerene-like shells and may
give rise therefore to an effective gas adsorption.
The aim of this chapter was to provide a detailed analysis of
previous measurements performed in experimental researches
focused on the performances of these materials for nitrogen
and oxygen sorption at various gas pressures, at various sample
temperatures and for different adsorption times [27, 28]. The main
results of these studies, carried out by the authors of this review,
have been published in Refs. [33, 34]. This chapter provides a more
detailed comparison with the results of similar studies by other
authors.
Studies of the sorption properties of fullerene C
, astralene
and activated carbon AG-3 powders have been performed by the
usual manometric (volumetric) method [19, 21]. The experimental
apparatus is described in Ref. [27]. It should be noted that in
order to carry out sorption measurements the pristine granules of
activated carbon have been milled up to a powder-like state.
For each kind of material the powders were placed into a flask
and degassed at 200°C in a 10
60
-4
torr vacuum for several hours. Then
molecular oxygen or nitrogen was injected into the system until
the required pressure in the flask was established. Each material
sample was immersed in the molecular gas medium for a fixed time.
A decrease in the pressure was detected upon gas adsorption by the
sample and the pressure measurements inside the system allowed to
estimate the amount of adsorbed gas. Control measurements of the
ratio between the volume of the flask with adsorbing material and
the remaining part of the system where a gas pressure is measured,
have been carried out with helium, that is not adsorbed by the
materials under our experimental conditions.
