Biomedical Engineering Reference
In-Depth Information
9.4 Mechanical properties of SC polymer-ceramic
nanocomposites
As a rule, particulate polymers improve a number of composite qualities
(including hardness, impact strength, work of disintegration and heat
resistance) [34]. This is mainly linked with the formation of a special
interfacial layer, as between the filler and polymeric binder. With regard to
conventional fillers, several specific properties of perovskite high-tempera-
ture superconductors (such as the layered structure, developed surface of the
ceramic grains, catalytic properties and free oxygen dislocated on the
surface of ceramic grains) will have an outstanding impact not only on the
formation of the phase boundary and consequently on the physical-
mechanical properties, but also on the superconducting (SC) properties of
the polymer-ceramic composites. This section is devoted to the discovery of
these issues.
Determination of the physical-mechanical properties of SC polymer-
ceramic nanocomposites is of interest not only at ambient temperatures, but
also in lower temperature ranges. Particularly interesting is their behavior at
the critical temperature of transition into the SC state. For SC polymer-
ceramic nanocomposites, the limiting strength of rupture (
σ
), elasticity
modulus (E) and elongation (
) were found to be at ambient temperatures
[20-27, 35], whereas with SHMPE binder, temperatures were found to be
close to 193K. The SC state temperature of the composite was 77K. The
magnitudes of
ε
were determined via distention of the samples at
ambient and 77K temperatures, and under compression conditions at
193K. In the latter case, the ceramic:binder ratio in the composites was also
varied.
The values of
σ
, E and
ε
are presented in Table 9.4. Juxtaposition of the
durability data for different binders shows that the highest rupture
resistance and elasticity modulus are observed for polyvinyl alcohol binder,
ethylene and tetrafluoroethylene copolymer, for practically the same filling
index. It is noteworthy that polymeric materials and filling systems with
lower usage temperatures produced enhanced durability and elasticity, but
simultaneously made deformity capabilities very inadequate. Deformation
ability is used as a criterion for the workability of polymeric materials,
especially at lower temperatures, which is why the measurements for
composites based on SHMPE were conducted at lower temperatures.
Compression durability measurements for composites based on SHMPE
(conducted at 193K) show that, for materials containing 90, 85 and 80%
weight of ceramic, the index is 34, 61 and 60MPa, respectively. Comparison
of the rupture properties at ambient and cryogen temperatures is also
interesting. Typical diagrams of elasticity for Y
1
Ba
2
Cu
3
O
6.97
nanocompo-
sites with SHMPE are presented in Fig. 9.7. It is apparent that for the same
σ
, E and
ε
