Biomedical Engineering Reference
In-Depth Information
Table 9.10 Superconducting characteristics of high-temperature SC ceramics
and polymer-ceramic nanocomposites based on Y
1
Ba
2
Cu
3
O
6.97
: SC transition
temperature (T
c
, K), the transition width (ΔT
c
, K) and the orthorhombic distortion
of the lattice structure (=(b - a)/a,η )
Type of polymeric binder (Y
1
Ba
2
Cu
3
O
7
x
:
polymer component = 85:15%)
ST:MMA
(40:60
mol%)
SPL (ST:MMA)
(80:20 mole%)
+NG-2246
Time,
(months)
SC characteristics
of specimens
Y
1
Ba
2
Cu
3
O
6.97
PS+NG
-2246
PE
0
η
0.0189
0.0185
0.0197
0.0194
0.0202
T
c
92.0
91.8
93.0
92.6
93.4
ΔT
c
6.5
6.5
7.0
6.5
9.0
6
η
0.0185
0.020
0.0185
0.0185
0.0185
T
c
91.7
92.8
91.7
92.1
92.2
ΔT
c
6.0
6.0
≈7
≈7
≈7
12
η
0.0185
0.0196
0.0181
0.0180
0.0180
T
c
91.8
92.8
91.7
92.0
92.0
ΔT
c
≈8
≈8
≈9
≈8
≈9
some insignificant property changes are reversible and can be ascribed to
auto-oscillating processes. Such auto-oscillating processes are typical for
structurally unstable electronic systems in solids, and cannot be attributed
to the aging of the structure. It seems that the Y
2
BaCuO
5
semiconductor
phase in Y
1
Ba
2
Cu
3
O
6.97
is the oxygen transport phase [46], which is present
in definite amounts in high-temperature SC ceramics, and supports the
stabilization of the SC characteristics on behalf of vacant oxygen positions.
Some increase in the T
c
value immediately after polymer-ceramic
nanocomposite formation is linked with intercalation of the fragments of
the macromolecule binders into the interlayer space between the ceramic
grains during the hot pressing process [25, 26].
The change in SC properties is dependent upon the chemical composition
of the polymeric binder, as kinetic investigations of the aging process in SC
polymer-ceramic nanocomposites have shown. The SC characteristics of
ST-MMA copolymers are worse, whereas in the case of the polyethylene
polymer, improvement is observed. An increase in the critical temperature
of transition for the SC state in nanocomposites with polyethylene binders is
possibly linked with processes taking place after the formation stages of
polymer-ceramic nanocomposites.
Previous work showed the presence of interactive forces between the
polymeric binder elements and the surface of the ceramic grains and the
intercalation of these elements into the interlayer space of the ceramic
particles. As it is evident from the data in Table 9.10, one can assume that
interaction of the elements of the polymeric binder with the surface of
