use of metal templates for microcavity formation in alumina

4.3.3. Ti Diffusion into Alumina
In this section, titanium diffusion into alumina was investigated. Figure 4.14(a)
and (b) show the picture of the sample after sintering for top and cross sectional view.
(a) (b)
Figure 4.14. Picture of the sample after sintering. (a) Top view and (b) cross sectional
view. Notice the dark spots on the cross section that correspond to the
location of Ti wire.
Electron microscope images of pressed alumina powders containing Ti wires
sintered at 1350 o C are shown in Figure 4.15. There are several similarities between the
five images, it is apparent in Figure 4.15.
(i) Each image shows a wide interdiffusion region around the Ti wire.
(ii) Each image shows some porosity and void formation aligned with the
wire.
The interdiffusion region is fractionally restricted in all five states rather than a
solid solution diffusion profile that would be more diffuse. The first justification of this
situation is compound formation. Next justification is that the diffusing types have come
across a barrier of some forms, perhaps connected to exhaustion or removed from a part
of the diffusion mechanism.
The cavity formation is a result of the creation of Kirkendall porosity
(Kirkendall, 1947) in which the vacancies are left behind by faster diffusing species that
coalesce into pores and in this case larger cavities (Goodshaw et al., 2009).
39