Hydrothermal Crystallization with Microstructural Self-Healing Effect on Mechanical and Failure Behaviors of Plasma-Sprayed Hydroxyapatite Coatings - Biological and Biomedical Coatings: Processing and Characterization - page 260

(a) (d)

Crystalline HA

0.8 µm 0.8 µm

(b) (e)

Self-healing

0.8 µm 1. 5 µm

(c) (f )

Self-healing

0.8 µm

0.8 µm

FIGURE 6.16
Surface morphologies of (a) HT100-12h, (b) HT150-6h, (c) HT150-12h, (d) HT200-6h, and (e) HT200-12h speci-
mens. Arrows indicate HA nanocrystallite crystallized through hydrothermal crystallization. (f) A significant
microstructural self-healing effect on lamellar boundaries and microcracks within HT150-6h specimen.

HACs during the hydrothermal treatment. Figure 6.18 shows the high-resolution XPS O 1 s
spectra of HT-HACs with curve fittings. The binding energy (BE) of these fit-peaks results
from the Gaussian peak-fitting routine. The O 1 s spectra presented in Figure 6.18a and b
consists of two components at about BE = 531.4 and 533.4 eV, which correspond to the PO
(PO 4 3− ) and POH bonds of HA crystal [176-178]. The relatively large integration area of the
POH bonding peak at HT-HACs specimens with high degree of crystallinity, as shown
in Figure 6.18b, can be recognized that the hydroxyl-deficient microstructure of plasma-
sprayed HACs is significantly improved with the abundant replenished OH − groups by
hydrothermal treatment. Beside the improved POH bond, previous reports indicated
that the HT-HACs specimen may exhibit a substantial amount of surface adsorbed