23.4.5 Heat Treatment of Novel Hydroxyapatites

The hydroxyapatite powders have potential applications as biomedical products in

the form of scaffolds and coatings on metallic implants; therefore, their high

temperature behavior needs to be understood. For this, heat treatment of

as-synthesized novel hydroxyapatites was done at 800 ^C, 1000 ^C, and 1200 ^C

for 1 h at a heating rate of 10 ^C/min in a silicon carbide furnace under controlled

atmosphere.

23.5

Ionic Substituted Nanodimensional Hydroxyapatites

23.5.1 Elemental Analysis of Novel Hydroxyapatites

The elemental analysis of as-synthesized novel hydroxyapatite powders was carried

out in order to confirm the substitution efficiency using wavelength dispersive X-ray

fluorescence spectroscopy (WD-XRF, Bruker, Germany). Approximately 8 g of

powder was used to make pellets of 1.5 mm thickness and 34 mm diameter. The

test was conducted for 17 min. Photoluminescence spectroscopy (PL) of

Eu-substituted HA powder was conducted using a Shimadzu UV-2401PC spectro-

photometer. The excitation was done at 325 nm wavelength of He-Cd laser with an

integrating sphere attachment using reference compound as BaSO4. Diffuse reflec-

tance UV-visible absorption spectra (DRUVS) were recorded. Micro-Raman and

photoluminescence studies were also conducted via Raman microscope by

Renishaw using a 514 nm wavelength of Ar laser.

The substitution of ions in hydroxyapatite was confirmed in all ionic substituted

powders though the concentration of substituted element was lesser than the amount

added during synthesis (Table 23.2). The substitution of ions in hydroxyapatite

affects its stoichiometry. The Ca/P of as-synthesized nanodimensional stoichiomet-

ric HA powder was 1.67. With ionic substitution, there is a deviation from a Ca/P of

1.67. Most of the as-synthesized nanopowders had Ca/P molar ratio less than 1.67

except for SiHA and KSiHA (Table 23.2).

PL of Eu-substituted nanodimensional HA powder showed the luminescence at

~590 nm and ~612.6 nm with the transition of 5D0 ! 7F1 and 5D0 ! 7F2 of Eu³⁺,

respectively. At higher wavelength region, the weak peaks also appeared. These

weak peaks might have occurred from direct excitation of Eu³⁺ from ground state to

higher levels in 4f6 configuration. The two prominent characteristic peaks from

5D0 ! 7F1 (590 nm) and 5D0 ! 7F2 (612 nm) were predominant in emission

spectra. These results infer that substitutions have occurred successfully in Ca sites

for cationic elements like K, Zn, Mg, Sr, and Eu; OH sites for anionic elements like

F; and PO4 sites for anionic elements like Si.

23

Unleashing Potential of Bone Mimicking Nanodimensional Hydroxyapatites and. . .

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