Biomedical Engineering Reference
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significantly dependent on the phases, detailed microstructure information such as the
individual thermal-sprayed splats acquired with the Raman spectroscopy is important.
Studies on thermal-sprayed splats can help to establish the understanding of individual
splat's contribution to the phase composition of the thermal-sprayed coatings. In addi-
tion, the crystallinity of plasma-sprayed HACs and phase composition at various locations
within individual thermal-sprayed HA splats have been quantitatively determined by the
Raman spectroscopy analysis [66,94,104,105].
In addition to evaluating the index of crystallinity, it is also important to quantify the
phase composition of amorphous component, crystalline HA, and other calcium phos-
phate phases of plasma-sprayed HACs by quantitative XRD analysis through the internal
and external standards. However, pure phases and mixtures with different compositions
are needed for establishing the calibration curves, and ACP is not easy to isolate and quan-
tify. Thus, the lack of full quantification and its long task of obtaining calibration curves
makes this technique unpopular. To fully determine the phase composition and quan-
tify the amount of decomposed phases, including the amorphous component, of the as-
sprayed coatings, the Rietveld method of structure determination from x-ray and neutron
powder diffraction patterns is another effective way and has widely been used to study
calcium phosphate compounds [60,106-111]. The Rietveld method creates an effective
separation of the overlapping data from x-ray and neutron diffraction patterns, thereby
allowing an accurate determination of the structure. This method has been successful and
today, the structure of materials in the form of powders is being determined. In addi-
tion, a more widely used application of the Rietveld method is in determining the com-
ponents of chemical mixtures. The conventional quantitative phase analysis (QPA), which
is carried out using relative peak height ratios of HA and other phases involved by the
Rietveld method provides a powerful tool that offers the user simultaneous quantitative
phase determination of multiphase systems containing amorphous content. The quantita-
tive analysis results of crystalline HA, amorphous, and various calcium phosphate phases
plasma-sprayed and crystallized HACs will be represented in the next section.
Figure 6.6a shows the surface morphology of the plasma-sprayed HACs. It displays a typ-
ical microstructural feature, which is composed of completely molten splats (indicated by
arrows), accumulated partially molten splats (marked by the circle), and thermal-induced
(a)
(b)
25 µm
25 µm
FIGURE 6.6
Typical plasma-sprayed HACs microstructural features for (a) surface morphology with microcracks, accu-
mulated splats (marked by circles), and molten splats (indicated by arrows). (b) Cross-sectional microstruc-
ture showing spraying defects including pores and microcracks. Circle marks residual partial molten particle
within plasma-sprayed HACs.
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