Biomedical Engineering Reference
In-Depth Information
a
b
c
0.355 nm
Bain strain
0.2
8
6 nm
0.251 nm
0.251 nm
Fig. B.5
Austenite-martensite transformation. Explanation see text. By courtesy of Prof. em. E.
Aernoudt
empty
site
AI(3+)
O(2+)
and
:Zr(2+)
:O(2-)
Fig. B.6
Crystallographic structure of (
left
) zirconia: f.c.c. packing of Zr with O in the tetrahedral
holes; (
right
) alumina: h.c.p. packing of oxygen ions with Al
3
C
only in two-thirds of the octahedral
holes (charge balance)
two tetrahedral holes for each atom of the f.c.c. structure, the formula is ZrO
2
.In
alumina, the oxygen atoms are hexagonally close-packed. The hexagonal structure
has one octahedral hole and two tetrahedral holes per atom with Al
3
C
put into the
octahedral interstices and each surrounded by six O
2
ions. In order to balance the
charges only two thirds of the sites are filled and the formula works out at Al
2
O
3
.
