Synthesis and
characterization of nanocrystalline hydroxyapatite ceramics
Authors: Bhatt,
H., and Kalita, S.J.
Year of Publication: 2005
Published in: Proceeding
of 107th Annual Meeting of the American Ceramic Society,
ABSTRACT
During
recent years, significant efforts have been made in developing nanostructured
bioceramics for tissue engineering applications. In our research, we have
synthesized nanocrystalline hydroxyapatite (Ca10(PO4)6(OH)2,
HAp) powders using ethanol-based and water-based sol-gel techniques at relatively
low temperatures. Calcium nitrate and triethyl phosphite were used as
precursors for calcium and phosphorous, respectively, in both processes. In the
ethanol-based method, triethyl phosphite sol was diluted in anhydrous ethanol
with a small amount of distilled water. A stoichiometric amount of calcium
nitrate, dissolved in anhydrous ethanol, was subsequently added drop wise into
the hydrolyzed phosphite sol to produce a transparent gel. As-formed gel was
aged for 16 h, then dried, and calcined at 350-850oC to produce nano
powder. In the water-based method, phosphorous and calcium precursors were
hydrolyzed in distilled water, separately, under vigorous stirring. Calcium
nitrate sol was added drop wise into the hydrolyzed phosphite sol and then aged
and dried. Calcination was carried out at 250-550oC. As-processed
powders were analyzed for their phases using an X-ray diffractometer and
characterized for their morphology and particle-size using a high-resolution
transmission electron microscope (HRTEM). HRTEM analyses showed that the
particle-size of the powders synthesized via ethanol-based and water-based
sol-gel techniques were 20-50 nm and 2-10 nm, respectively. Further, these
nano-powders were uniaxially compacted and then sintered at 1300oC
for 6 h in a muffle furnace to study their densification behavior. An average
sintered density of 2.90 g/cc, equivalent to 91.8% of the theoretical density
of HAp (3.16 g/cc), was achieved in structures made of the powder synthesized
using ethanol-based sol-gel route. Whereas, the highest average sintered
density (3.12 g/cc) was achieved in structures made of the powder produced via
water-based route, which is equivalent to 98.7% of the theoretical density of
HAp. Results of Vickers hardness testing on sintered structures showed that
structures of powder produced via water-based route had higher hardness in
comparison to the ethanol-based ones. Uniaxial compression tests showed average failure strengths 31
MPa and 41 MPa for ethanol-based and water-based nanostructures, respectively. © 2005 American Ceramic Society.
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