Effect of Preparation Temperature on Crystal Structure and Magnetic Properties of Nanophase Fe-Substituted Hydroxyapatite

The purpose of the study is to investigate the effect of preparation temperature on the
crystal structure and magnetic properties of nanophase Fe-substituted Hydroxyapatite. Multisubstituted
Hydroxyapatite (HAp), Ca5(PO4)3OH, is the main mineral phase in physiological
apatite, ~70 wt% in bones and dentin, and ~96 wt% in enamel. Iron is one of the minor
substitution elements (0.01-0.1 wt% in bone and 0.003 wt% in enamel) replacing Ca in the HAp
structure. Research interest on Fe-HAp is related to the fact that Fe for Ca substitution reduces
the solubility of HAp therefore it functions as a cavities preventive agent. In contrast, Fe
overload causes a decrease in bone mechanical strength. Furthermore, Fe-HAp can find
applications in hyperthermia based anti-cancer treatments and in magnetic resonance imaging
(MRI) contrast agents. Two sets of Ca5-xFex(PO4)3OH samples (x=0,0.05,0.1,0.2,0.3) were
synthesized by a chemical precipitation method at physiological temperature (370C) and 800C.
The samples were calcinated at 6500C and deuterated at 6000C. The samples were characterized
by x-ray powder diffraction (XRD), neutron powder diffraction (NPD) and SQUID
Magnetometry. A single-phase system was detected for nominal iron content x≤0.1 by XRD
phase identification in both sets of samples, while hematite (α-Fe2O3) and/or maghemite (γ-
Fe2O3) develops starting at x=0.1. According to the magnetic measurements, sample with x=0
showed diamagnetic behavior while samples with Fe showed paramagnetic behavior. Combined
Rietveld refinements of XRD and NPD patterns will provide accurate information on the effect
of processing temperature on the crystallographic parameters of the nano-materials.