Biomedical Engineering Reference
In-Depth Information
nanostructured composite coatings, the use of polymer-derived ceramics
to join ceramics and the processing of controlled porosity ceramics (e.g.
in-situ carbon nanotubes in a ceramic matrix)
.
nanostructured ceramics for fuel cell and battery applications, including
the development of various state-of-the-art materials for solid oxide fuel
cells (SOFC) and nanostructured ceramics that enable the operation of
SOFC in a temperature range of 500-650
C. It appears that the doping
of nanosized Ag in Li-CoO 2 cathodes increases the electrical
conductivity by two to three orders of magnitude with reference to
undoped materials. The synthesis of nanocrystalline Li 4 Ti 5 O 12 using an
aqueous combustion process with alanine fuel will be the subject of
future research.
8
It seems likely that there will be intensive development of ceramic- and
carbon-based filler nanocomposites in the near future. In addition to carbon
nanotubes and carbon nanofibres, new carbon-based fillers such as graphene
and graphene platelets (GPL), also called graphene nanoplatelets (GNP)
and/or multi-layer graphene nanosheets (MGN), offer alternatives to the
more expensive nanotubes. Currently, there are only a few reports on the use
of graphene additives
to improve the mechanical and/or
functional
properties of bulk advanced ceramics.
A graphene nanosheet/alumina composite has been prepared by Wang
et al. (2011) using spark plasma sintering. The results show that the fracture
toughness and conductivity of the graphene nanosheet/alumina composite
are about 53% and 13 orders of magnitude higher than those of
unreinforced alumina material, respectively. Walker et al. (2011) applied
aqueous colloidal processing methods to obtain uniform and homogeneous
dispersions of GPL and Si 3 N 4 ceramic particles which were densified using
spark plasma sintering. A fracture toughness of 6.6MPam 0.5 was measured
for a composite with 1.5 wt% of GPL, which was significantly higher than
the value measured for the monolithic silicon nitride with globular grains of
α
￿ ￿ ￿ ￿ ￿ ￿
-phase. The observed toughening mechanisms on the fracture surfaces of
the nanocomposites are in the form of graphene necking and crack bridging,
crack deflection and graphene sheet pull-out. Kun et al. (2011) prepared and
characterised silicon nitride based nanocomposites with differing amounts
of carbon reinforcement in the form of multilayer graphene, graphite
nanoplatelets and nano-graphene platelets. They found that both the
bending strength and elastic modulus decreased with the addition of carbon-
based fillers and that the composite with multi-layered graphene exhibited
the highest strength and module of elasticity among the composites.
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