Biomedical Engineering Reference
In-Depth Information
Fig. 7.12
The crack stopper. Parallel packing of lamella or needle-like crystals will stop the
crack line to penetrate the bundled crystallites. (
a
) The mosaic structure of a crystal causes the
propagation of crack line, leading to the breakage of the crystal. (
b
) The parallel packing of lamella
or needle-like crystallites in a crystallites assembly will stop the propagation of the crack line from
one crystallite to the adjacent crystallites
units are incorporated into the crystal phase. This will slow down the nucleation
kinetics, whose effect is contrary to the effect of lowering the nucleation barrier. As
mentioned above, the latter effect, the so-called
shadow effect
of the substrate, is
reflected in the appearance of
f
(
m
)and
f
(
m
) in the pre exponential term of (
7.32
).
These two controversial effects play different roles in different regimes. At low
supersaturations, the nucleation barrier is very high (cf. (
7.33
)and(
7.34
)). The
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