Biomedical Engineering Reference
In-Depth Information
13.10 Relationship between dihedral angle and critical pore
coordination number.
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The effects of green density and agglomeration on densification can be
explained by the pore coordination number theory. Higher green density
and less agglomeration result in fine and uniform pores that shift the pore
coordination number distribution from high values to low values, i.e. more
pores fall into the category below the critical pore coordination number.
These pores are easily removed during sintering and thus lead to denser
products. As for the large pores that are thermodynamically stable and have
coordination numbers higher than the critical value, a process by which the
coordination number can be reduced during sintering is essential, since the
pores will again become unstable and the densification will then continue.
Particle rearrangement and grain growth are the two processes that can play
this role, creating a dilemma, of course, and difficulty for any attempt to
achieve maximum densification without grain growth.
13.4 Grain growth during sintering of nano particles
13.4.1 The unique issue of grain growth during sintering
of nano particles - significance of non-isothermal
grain growth
A primary motivation for studying sintering of nanosized particles is rooted
in the issue of rapid grain growth during sintering. In many cases,
particularly when the goal is to produce nanocrystalline bulk materials, the
objective of sintering of nano particles is to achieve full densification as well
as the retention of nanoscaled grain structure in the sintered material.
