Biomedical Engineering Reference
In-Depth Information
ceramic grains, although slow, nevertheless proceeds at ambient tempera-
tures through the intercalation mechanism. For this reason, some increase in
T
c
is observed (1-1.5 degrees).
As already stated, for the SC nanocomposites of ST with MMA
copolymers, the aging process results in a decrease in T
c
by 1-1.5
8
C, an
increase in
. The presence of an antioxidant (NG-
2246) does not influence the stated characteristics. These kinds of
characteristic changes can be explained by the enhanced inclination of the
ST-MMA copolymer binders towards destruction under the impact of
ultraviolet radiation. To obtain more substantial data on the elevation of T
c
during the aging of polymer-ceramic nanocomposites based on the
polyethylene matrix, similar investigations have also been carried out on
the samples obtained by the gas-phase polymerization of ethylene in the
presence of Y
1
Ba
2
Cu
3
O
6.97
ceramics.
Δ
T
c
and a decrease in
η
9.8.1 Preparation of SC polymer-ceramic nanocomposites
by gas-phase polymerization of ethylene
The catalytic properties of oxide ceramic perovskites have been known for a
long time [47-49]. As a result, questions have naturally been posed over the
issue of catalytic activation of a ceramic surface for polymerization of gas-
phase monomers (ethylene, propylene, etc.) without the use of polymeriza-
tion catalysts on the surface. Presumably, the layered structure of the
crystalline orthorhombic phase will allow coordinating ethylene (or other
kinds of olefins) on the surface of the Y
1
Ba
2
Cu
3
O
7
x
ceramic grains and, in
this case, the polymerization process may proceed in the presence of
polymerization (alkyl-aluminum) co-catalysts.
It should be noted that, in this case, the quantity of forming polymer was
regulated by the polymerization time permitted for the preparation of
nanocomposites with various binder contents. In this case, there is the
Meissner effect on all samples that did not have added antioxidants. This is
explained by the decreasing diffusion velocity of oxygen located on the
surface of the ceramic grains as a result of the formation of the polymer
covering around the oxide ceramic particles. Parallel displacement of curves
on the SC transition towards enhancement of T
c
from 46K (for initial
ceramics) up to 70K (Fig. 9.19) with increasing polyethylene content was
observed [19-21].
The decrease in T
c
in the initial Y
1
Ba
2
Cu
3
O
6.97
ceramics from 92K up to
46K, and accordingly for the obtained nanocomposites, is possibly linked to
high-temperature activation of the surface of the ceramic grains. During
development of the SC state, three transition temperatures were detected on
the curves (Fig. 9.19) of the SC transition for all of the nanocomposites: low
