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The high-temperature mechanical properties of
a newly developed silicate-based glass
sealant, designated as GC-9, have been studied for use in planar
solid oxide fuel cell
(pSOFC). Both bulk and sintered GC-9 glass specimens were made for
studying the
high-temperature mechanical behavior. In order to investigate
effects of crystallization,
the as-cast bulk GC-9 glass was treated at 900oC for 3 h
and the sintered GC-9 glass was
aged at 750oC for 100 h. Not only crystalline phases were
formed but the residual glass
was also changed in the aged bulk GC-9 glass after heat treatment.
On the other hand, a
different fabrication process generated pores and different
crystalline phases in the sintered
GC-9 glass from the bulk one. Such different microstructure and
crystalline phases
resulted in different high-temperature mechanical properties.
Four-point-bending tests
were conducted at 25oC, 550oC, 600oC,
650oC, 700oC, and 750oC to
investigate the
variation of flexural strength and elastic modulus with temperature
for both the non-aged
and aged bulk GC-9 glass. For the non-aged and aged, sintered GC-9
glass, ring-on-ring
tests were carried out at 25oC, 650oC, 700oC,
750oC, and 800oC to investigate the variation
of flexural strength and elastic modulus with temperature. Weibull
statistic analysis was
applied to describe the fracture strength data.
The glass transition temperature (Tg) of the bulk glass is reduced
but the softening
temperature (Ts) is increased by heat treatment at 900oC
for 3 h. From the
force-displacement curves of the sintered GC-9 glass, the transition
temperature from
brittle to ductile behavior was estimated. The inferred Tg of the
non-aged, sintered GC-9
glass was between 700oC and 750oC, while that
of the aged one was between 750oC and
800oC. The Tg was an index for distinguishing the
influence of crystalline phases and
residual glass on the mechanical properties. The aged bulk GC-9
glass exhibited a greater
flexural strength and Young’s modulus than did the non-aged bulk one
at temperature
below 650oC due to existence of the crystalline phases.
At temperature of 700oC and
750oC, a greater extent of stress relaxation was found in
the aged bulk GC-9 glass such that
its strength and stiffness were much lower than those of the
non-aged bulk one. However,
the sintered GC-9 glass with pores and crystalline phases showed a
flexural strength lower
than the bulk one at temperature of 650oC and below. Due
to a greater extent of
crystallization, the flexural strength and stiffness of the sintered
GC-9 glass were greater
than those of the bulk one at 700oC and 800oC.
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