Biomedical Engineering Reference
In-Depth Information
4.1
Typical ceramic nanocomposites (after Niihara
et al
., 1993).
One means of overcoming these drawbacks is the preparation of
composite materials, where the base ceramic matrix is reinforced by
secondary phases in the form of particles, platelets, whiskers or fibres. These
additives act in a variety of ways. In general, their role is to dissipate the
energy of crack propagation by deflecting and arresting cracks caused by the
presence of residual stress fields, crack bridging, crack branching, micro-
cracking and other micro-mechanisms.
In recent years, there has been great interest in 'nanoceramics'. The
concept of structural ceramic nanocomposites was proposed by Niihara
et al. (1993) and was based on results achieved during the study of
Si
3
N
4
+SiC and Al
2
O
3
+SiC systems. Nanocomposite ceramics may be
defined as composites consisting of more than one solid phase, where at least
one of the phases has a nanometric dimension. These nanophases are
generally nanoparticles located inside matrix grains and/or at the grain
boundaries. Depending on the location of the nanophases, nanocomposites
may be classified as inter-type,
intra-type,
inter/intra-type and nano/
nanotype (Fig. 4.1).
