vibrational mode at 569 cm1 and 602 cm1 and 1039 cm1. Similarly, MgHA
showed decreased intensities of OH vibrations at 3568 cm1 and 633 cm1 and
significant broadening at 700–1700 cm1 for PO4
3. In EuHA nanopowder, all the
characteristic peaks of hydroxyapatite were observed but with decreased transmit-
tance. In FHA nanopowder, OH vibrations at 3569 cm1 and 631 cm1 were
absent. The characteristic band of OH...F...OH appeared at 721 cm1. In SiHA and
KSiHA nanopowders, bands corresponding to orthosilicate group appeared at
504 cm1 and 892 cm1, respectively. In MgSrHA nanopowder, phosphate bands
of ν1 PO4
3 and ν4 PO4
3 shifted towards lower frequency. The weak absorption
peak at 875 cm1 attributed to P-O-H vibration of HPO4
2 was also observed.
However, the band of OH...F...OH appeared at 716–727 cm1 in ZnFHA, SrFHA,
and MgSrFHA nanopowders.
The FTIR spectra of all heat-treated nanopowders showed almost similar patterns
with decreased intensities. On heat treatment of ZnFHA nanopowders, the loss in
intensity of the hydroxyl groups was observed around 3570 cm1 (Fig. 23.7).
The vibration at 874 cm1 related to P-O-H in HPO4
2 disappeared on heat
treatment, whereas peaks of phosphate became strong. In heat-treated ZnFHA
nanopowders, bands ascribed to configuration FFOHFF were seen at 740 cm1. In
SiHA and KSiHA heat-treated nanopowders, orthosilicate group (ν1 symmetric stretch,
~752 cm1; ν2 bending, ~504 cm1; ν3 asymmetric stretch, ~892 cm1) was observed.
23.5.3 Thermal Stability of Novel Hydroxyapatites
The thermal behavior of as-synthesized HA and FHA nanopowders was investigated
by thermogravimetric (TGA)/differential scanning calorimetry (DSC)/differential
thermogravimetric (DTG) techniques. The approximate weight of samples taken
Fig. 23.6 FTIR spectra of as-synthesized fluorine-substituted hydroxyapatite nanopowder
440
S. Kapoor et al.