Biomedical Engineering Reference
In-Depth Information
9.18 Density-temperature diagram for three regimes of frontal
polymerization [28].
reduces and limits the yield of nanocomposites. The upper temperature limit
(200
8
C) is determined by the thermal degradation of the nitrate groups in
the nanocomposites obtained.
The influence of density, temperature and reactor diameter on the
structure of heat waves, rate of front propagation and range of existence of
steady-state regimes was investigated. Experimental results obtained at
different temperatures and densities are summarized in Fig. 9.18. Here,
curve 2 is the domain of steady-state heat polymerization waves, which is
limited by the straight line corresponding to limiting packing of the reaction
media (
r
lim
) and full melting of the crystalline monomer. There are no wave
regimes of
frontal polymerization below curve 1, when
r> r
lim
and
T
T
melt
.
For mass ratios of the ceramic:metal polymer
≥
80:20, the addition of
minute quantities of Y
1
Ba
2
Cu
3
O
7
x
does not allow frontal waves to travel
from up to down, at temperatures up to 100
≤
C. At the same time, the
formation of the propagating frontal regimes of heat waves is observed at
temperatures above 60
8
C, when the wave initiates from the bottom and
propagates from bottom up. This situation is explained by the gas evolution
during frontal polymerization, as well as by the inhibition of some
constituents of the gases evolved from the process of polymerization.
The results of an investigation into the SC properties of Mn-, Co-, Ni-
and Zn-containing polymer-ceramic nanocomposites are presented in Table
9.9, which shows that the onset of the transition into the SC state (T
c
)is
shifted towards higher temperatures in comparison to the initial ceramic,
8
