hydroxyapatite;

JCPDS

Card

No.

15-0876

for

fluorapatite;

JCPDS

Card

No. 09-0348 for α-tricalcium phosphate (α-TCP); JCPDS Card No. 09-0169 for

β-tricalcium phosphate (β-TCP). The structural stability of heat-treated powders was

also assessed from the phase transformations at higher temperatures. As reported by

Dorozhkin (2003), Cullity and Stock (2001), and Kannan et al. (2007), the thermal

decomposition of CDHA (Ca10
x(HPO4)x(PO4)6
x(OH)2
x) takes place above

1000 ^C, resulting in biphasic mixture consisting of hydroxyapatite phase (HAp)

and β-tricalcium phosphate phase, the equation for which is given below:

Ca10
z HPO4

ð

Þx PO4

ð

Þ6
x OH

ð

Þ2
x ! 1
x

ð

Þ Ca10 PO4

ð

Þ6 OH

ð

Þ2

þ 3xCa3 PO4

ð

Þ2 þ xH2O

ð23:1Þ

where Ca/P ¼ (10
x)/6 and x is the calcium deficiency.

The mole fractions XHA, Xβ-TCP, and Xα-TCP of pure HA, β-TCP, and α-TCP

phases present in various powders were determined. The external standard method

was used to calculate the weight % of hydroxyapatite phase (WHAp) and β-TCP

phase (Wβ-TCP) from XRD patterns. The weight % were then converted into mole

fractions and used for calculating x and Ca/P values. The crystallinity degree (Xc) of

nanopowders was calculated using the equation given below:

Xc ¼ 1
V112=300=I300

ð23:2Þ

where V112/300 is the intensity of hollow between (1 1 2) and (3 0 0) peaks and I300 is

the intensity of (3 0 0) peak of HA. Verification for crystallinity was done according

to the equation given below (Landi et al. 2000):

Fig. 23.3 TEM micrographs of heat-treated novel hydroxyapatites

23

Unleashing Potential of Bone Mimicking Nanodimensional Hydroxyapatites and. . .

433