Biomedical Engineering Reference
In-Depth Information
the filler and the binder. It is noteworthy that the issue of stability of the
properties of a polymeric binder is disputable if it has a three-dimensional
structure. Nevertheless, the influence of filler particle size and the nature of
the binder on the physical-mechanical properties of composites based on
epoxy binders has been demonstrated [20, 24, 26].
The results of investigations into the influence of filler particle size and
concentration on the physical-mechanical properties of polymer-ceramic
nanocomposites, obtained on the basis of Y
1
Ba
2
Cu
3
O
6.97
and divinyl rubber
(DR), are outlined in Table 9.5. The table shows the influence of the size and
filling degree of particles on
and E and also on the beginning (T
c
)and
end (T
f
) temperatures of the transition into a superconductive state for
nanocomposites with cross-linked DR. The data indicate that the higher the
ceramic content, the higher the rupture strength and modulus of elasticity
and the lower the limiting deformation, which are all independent of the
particle size of the Y
1
Ba
2
Cu
3
O
6.97
.
The considerable increase in
ε
,
σ
and E with an increase in the rate of filling
evinces the presence of full contact in the polymer-filler interface and the
absence of scaling of the binder from the filler during the deformation of the
tested samples. The absence of scaling is also indicated by the stress-
deformation curves (Fig. 9.7), where no yield point (point of fluidity) is
observed. These results confirm the earlier conclusion [25, 26] about the
existence of sufficiently strong interactions between the binder and the
surface of the Y
1
Ba
2
Cu
3
O
6.97
ceramic grains.
This is additionally confirmed by data on the influence of ceramic grain
size on
σ
and E for the same filling rate. Furthermore, as outlined in Table
9.5, an increase of the mean filler size decreases the values of
σ
and E. This
fact can be explained by the diminution of the general contacting surface of
the binder with the filler, causing the general energy of their interaction to
reduce, and consequently decreasing the limiting strength and modulus of
elasticity.
It is interesting that, with an increase in the average particle size, a
tendency for increased composite deformation capacity is observed. It is
probable that the increase of particle size has a positive effect, providing
enhancing efficiency in preventing the propagation of cracks at high degrees
of deforming capacity. Table 9.5 also provides data on the influence of
average ceramic grain size on critical temperature, both at the beginning of
the SC transition (T
c
) and at its end (T
f
).
The initial non-fractioned Y
1
Ba
2
Cu
3
O
6.97
ceramic possesses the char-
acteristics of: T
c
=93K and T
f
=87K. Juxtaposition of the initial ceramic
composite with DR, plus different ceramic particle size, results in dissimilar
SC properties. For nanocomposites with a mean particle size of 5-10
σ
m, the
value of T
c
is lower by 5-10 degrees than in the original ceramic. In
addition, the transition width (T
c
μ
T
f
) widens. When the mean particle size
