Biomedical Engineering Reference
In-Depth Information
FIGURE 18.7
Secondary ion images of a PLA microsphere at different stages of FIB sample preparation: (A) top view of
ion-milled trenches, scale bar is 15
μ
m and (B) fully undercut sample, scale bar is 10
μ
m
[44]
.
18.2.3.1 XRD Case Studies
Cengiz et al.
[48]
used XRD to characterize nanoparticles of a novel calcium phosphate growth medium
referred to as CaP-Tris. This was prepared by mixing Tris HCl,
2
OH)
3
CNH
2
), HCl, K
2
HPO
4
, and CaCl
2
in deionized water. This new formulation was compared with a reference hydroxyapatite (HA) powder.
Figure 18.8
shows the XRD patterns of reference HA and CaP-Tris. As can be seen, the XRD patterns
are almost identical in terms of peak position and relative intensity. Thus, HA nanoparticles have been
synthesized by a new precipitation method and CaP-Tris calcium phosphate growth medium.
18.2.4
Mercury Porosimetry
Mercury porosimeter is a device which is capable of generating suitably high pressures and meas-
uring simultaneously both the pressure and volume of mercury taken up by a porous material
[49]
.
Mercury does not wet most substances and will only penetrate pores when forced to do so under high
pressure. Entry of mercury into pores requires applying pressure in inverse proportion to pore size.
In other words, large pores will fill first, with smaller pores filling at increasingly higher pressures.
Equation (18.2), known as the Washburn equation, is the basis of the mercury porosimeter method for
measuring pore size distribution:
4
γ
cos
θ
D
(18.2)
P
where
D
is the pore diameter,
γ
the surface tension,
θ
the contact angle, and
P
the applied pressure.
Mercury exhibits a high contact angle against most solids. Reported contact angles vary, with 130°
