Chemistry Reference
In-Depth Information
Hexagonal
closest
packing of spheres
cubic closest or
face-centred
packing of spheres
cubic
body-centred
packing of spheres
Coordination number 12
Coordination number 12
Coordination number 8
number of spheres
number of spheres
number of spheres
Total: 6
Total: 4
Total: 2
Fig. 10.10 Elementary units and unit cells of the three metal structures
a-
Fe
b-
Fe
g-
Fe
d-
Fe
Iron melt
768°c
906°c
1401°c
1535°c
Fig. 10.11 Different iron structures depending on temperature
structural change at 906
C: the cubic body-centered structure changes to a cubic
face-centered structure [
11
]. Figure
10.11
shows different modifications of iron and
corresponding structures:
b
-iron only differs from isostructural
a
-iron by the
disappearance of magnetism at 768
C.
The ductility of
-iron in the given temperature range can be explained with the
high symmetry of the cubic face-centered structure: close-packed layers of atoms in
g
