Biomedical Engineering Reference
In-Depth Information
an unstable phase is a feature of current-generation SC ceramics. Non-
stability of the lattice structure is linked with the deficiency of the atoms of
oxygen in the elementary cell, accompanied by the accumulation of regular
patterns of vacancies in the Cu-O atom chains. As a result, the increase of
non-stability in the lattice structure of the Y
1
Ba
2
Cu
3
O
7
x
ceramic over time
can change its SC characteristics, for example its critical temperature of
transition into the SC state (T
i
, K) or the width of transition (
Δ
T
c
, K).
9.2 Material preparation, characterization and testing
In order to study the effects of different preparation factors, powders of the
corresponding polymer and Y
1
Ba
2
Cu
3
O
7
x
ceramic were preliminarily
blended in an agate mill to give a homogeneous mixture for the formation of
items (plate, rod, tube, ring, etc.). These pre-made mixtures were then filled
into previously heated (130, 150, 160, 200
8
C) forms and pressed at 100mPa
for 5, 10, 20, or 30min.
In another series of experiments focused on the formation of polymer-
ceramic SC items from Y
1
Ba
2
Cu
3
O
7
x
ceramic powder at ambient
temperature, specimens were pressed with follow-up imbibing of methyl
methacrylate, both with initiator (azobisisobutyronitrile (AIBN)) and
without. To counterbalance vaporization of the monomer, the specimens
were placed in sealed glass forms and polymerized at 60-80
C. As a control
for the reaction end, other specimens were tested concomitantly in a DAK-
11 microcalorimeter.
For
8
the
gas-phase
polymerization
of
ethylene
influenced
by
Y
1
Ba
2
Cu
3
O
6.97
(particle size
C
over the course of 4 hours, then cooled down to ambient temperature in a
dry air environment. Part of the thus-obtained ceramic was used for the
determination of the critical transition temperature to the SC state, whilst
the other part was placed in the polymerization reactor. At room
temperature, under a pressure of 20 bar, ethylene was introduced into the
reactor filled with hexane, and alkyl aluminum was injected under vigorous
agitation (rotation speed of 100 rpm). Ethylene was consumed for 3 hours,
which is a major sign of ethylene polymerization.
Structures of the high-temperature SC ceramic and its composites were
determined using X-ray analysis on a DRON 2.0 instrument (
50
μ
m), the surface was activated at 197
8
<
λ
CuKr) in the
15
8
≤
20
8
≤
130
8
range of angles at
room temperature. The
critical
temperatures of the SC transitions were measured by the
C-magnetic
susceptibility method at a frequency of 1 kHz, when the amplitude of the
magnetic field was 10mE. The physico-mechanical properties were
determined on an INSTRON rupture machine, and thermo-oxidation
destruction was monitored via a derivatographic method using a MOM
brand Q-1500 instrument.
α
