Biomedical Engineering Reference
In-Depth Information
(a)
(b)
25
35
45
55
20
30
40
50
60
2
θ
FIGURE 6.5
X-ray diffractions of (a) well-crystallized HA powder and (b) plasma-sprayed HACs.
in peak intensity and peak broadening of HA peaks suggest the formation of ACP [103].
The formation of these phases is a result of HA phase decomposition and dehydroxylation
affected by extreme temperatures of plasma flame, rapid solidification, and highly reactive
atmospheres that favor nonequilibrium or metastable structures according to the reactions
described before. Plasma-sprayed HACs typically have high defect contents, amorphous
components, and residual stresses, which result in a broadening of the x-ray diffraction
peaks. In addition to providing the variation in phase composition, another material char-
acteristic of plasma-sprayed HACs obtained through the x-ray diffraction analysis is the
index of crystallinity. The crystallinity has been defined in different ways for biomedical
applications, and it was initially used as an indication of the crystal size or perfection of
the crystal lattice in HA crystals [98]. In order to quantitatively evaluate the crystallinity
of plasma-sprayed HACs, a commonly used index of crystallinity (IOC) defined the ratio of
the three strongest HA main peaks ((211), (112), and (300), JCPDS 9-432), the integral inten-
sity of the plasma-sprayed HACs (
I
c
), and the well-crystallized single HA phase starting
powders (
I
p
) according to the relationship IOC = (
I
c
/
I
p
) × 100% [99-102]. As shown in Figure
6.5a, this method supposes that the IOC of the well-crystallized HA is 100%. According to
this method, the IOC value of plasma-sprayed HACs with a diffraction pattern as shown
in Figure 6.5b is about 20.3% [101].
Although x-ray diffraction has been a conventional and effective analysis method to
obtain the phase composition and quantitative phase content of plasma-sprayed HACs,
the limitation is that x-ray diffraction can only detect phases and provide an average value
within a large area. It cannot provide sufficient information when amorphous compo-
nents are the major products. Therefore, the feasible technique of Raman spectroscopy
provides another way to reinforce the application of the x-ray diffraction method. The
Raman spectroscopy can provide information on the short and intermediate range order-
ing in the solids and it allows a direct and nondestructive detection from the sample sur-
face. Since both in vitro and in vivo biological properties of plasma-sprayed HACs are
Search WWH ::
Custom Search