Thermal Sprayed Bioceramic Coatings: Nanostructured Hydroxyapatite (HA) and HA-Based Composites - Biological and Biomedical Coatings: Processing and Characterization - page 160

5.0 mM K + , 1.5 mM Mg 2+ , 2.5 mM Ca 2+ , 147.8 mM Cl − , 4.2 mM HCO 3 − , 1.0 mM HPO 4 2− , and
0.5 mM SO 4 2− . The in vitro test was conducted in a continuously stirred bath containing
distilled water with a stable temperature of 37°C.
As already reported (Li et al. 2004c), the Raman spectra at 200 to 900 cm −1 region of the
thermal-sprayed HA splats (as-sprayed and heat-treated) with the comparison to those
of reference materials are shown in Figure 4.18. While the Raman spectra of the plasma-
sprayed HA splats (as-sprayed and heat-treated) at 900 to 2000 cm −1 region are typically
shown in Figure 4.18d. It is noted that for the plasma-sprayed HA splats, there is a lack of
obvious Raman shifts at the miscellaneous locations, as shown in Figure 4.18a(d,e,f) and
Figure 4.18d(d,e,f). The broadening and featureless bands at vibration modes u 1 (~950 cm −1 ),
u 2 (~430 cm −1 ), u 4 (~596 cm −1 ), and the almost unobservable peaks of u 3 (~1032-1081 cm −1 ) are
typical features of ACP structure (Wen et al. 2000). These indicate the presence of uniform
ACP phase within the splat; a result of fully melted HA powders during the plasma-spray
process. Upon heat treatment, the bands of the respective vibration modes were narrowed,
with an increased intensity and splitting of peaks (u 2 : 428 and 447 cm −1 ; u 3 : 1029, 1044, and

608

(a) 590

447

(b)

432

(a)

240 (a)

(b)
(c)

432

277 591

(b)
(c)
(d)

(d)
(e)
(f )

200 300 400 500 600 700 800 900
Raman shift (cm −1 )

200 300 400 500 600 700 800 900
Raman shift (cm −1 )

960

(c) (d)

711

358

281

689 (a)

950

253

(b)

(c)

(d)
(e)
(f )
(b)
(a)
(c)
900 950 1000 1050 1100 1150 1200

(d)

(e)

200 300 400 500 600 700 800 900
Raman shift (cm −1 )

Raman shift (cm −1 )

FIGURE 4.18
[a] Raman shifts of heat-treated HA splat (plasma-sprayed) at (a) middle, (b) edge, and (c) center, and as-plasma-
sprayed HA splat at (d) edge, (e) middle, and (f) center of splat. [b] Raman shifts of a big HVOF splat at (a)
center, (b) edge, and a small HVOF splat at (c) center and (d) edge. [c] Raman shifts of the reference materials (a)
Ca(OH) 2 , (b) CaCO 3 , (c) CaO, (d) α-TCP and (e) β-TCP. [d] Raman shifts of a typical heat-treated HA splat (plasma-
sprayed) at (a) middle, (b) edge, and (c) center, and as-plasma-sprayed HA splat at (d) edge, (e) middle, and (f)
center. (From Li et al., Acta Mater. , 52, 445-453, 2004c. With permission.)