Biomedical Engineering Reference
In-Depth Information
Table 9.1
Superconducting properties of polymer-ceramic nanocomposites
after restoration
Composite
Ceramic:binder
weight ratio
T c (K)
T f (K)
Notes
SHMPE + Y 1 Ba 2 Cu 3 O 7 x
80:20
85:15
85:15
96
96
96
84
84
84
Obtained after the
restoration stage
RPE + Y 1 Ba 2 Cu 3 O 7 x
80:20
94
80
Obtained after the
restoration stage
Ф
-40 + Y 1 Ba 2 Cu 3 O 6.97
75:25
96
77
Obtained after the
restoration stage
PB + Y 1 Ba 2 Cu 3 O 7 x
80:20
96
83
Obtained after the
restoration stage
PVF + Y 1 Ba 2 Cu 3 O 7 x
85:15
90
75
Obtained after the
restoration stage
PFA + Y 1 Ba 2 Cu 3 O 7 x
80:20
88
76
Obtained after the
restoration stage
SHMPE + Irganox +
Y 1 Ba 2 Cu 3 O 7 x
80:20
96
89
Obtained without
restoration
RPE + Irganox +
Y 1 Ba 2 Cu 3 O 7 x
80:20
94
85
Obtained without
restoration
PVA + Irganox +
Y 1 Ba 2 Cu 3 O 7 x
85:15
90
80
Obtained without
restoration
superconducting transition. For the polyformaldehyde composition, the
considerable T c decrease can be explained by the high inclination of
polyformaldehyde towards thermo-oxidative destruction, which enhances
the consumption of oxygen in the ceramic. Moreover, even at the
comparatively lower temperature [30] of polyformaldehyde thermo-oxida-
tion, this was accompanied by a de-polymerization reaction; the resultant
release of gaseous formaldehyde could, in turn, adversely affect the SC
properties of the nanocomposites.
￿ ￿ ￿ ￿ ￿ ￿
9.3.1 Influence of thermal regimes on the SC properties of
polymer-ceramic nanocomposites
To ensure steady contact between the polymeric binder and the ceramic
grains, hot pressing of the mixture should be performed at temperatures
slightly exceeding the melting or vitrification temperature of the polymeric
matrix. The temperature of vitrification for acryl and vinyl homo- and
copolymers does not exceed 100
8
C, whilst the melting temperature of the
polyolefins is 120-125
8
C (apart
from polypropylene (PP),
for which
T melt =170-175
8
C). This is why most samples studied were pressed at 130
8
C.
8
C, samples sustain their SC properties. Nevertheless,
the samples based on polyethylene possess the same values of T c and
After pressing at 130
Δ
T c as
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