Synthesis and characterization of hydroxyapatite (HA) and silicon substituted hydroxyapatite (SI-HA) produced by a precipitation method
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Date
2009
Authors
Le, Thi Bang
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Abstract
The precipitation method is a successful route to synthesize high purity
hydroxyapatite (HA) and silicon-substituted hydroxyapatite (Si-HA) at low
temperatures. In this research, calcium hydroxide (Ca(OH)2) and phosphoric acid
(H3PO4) were chosen as starting materials to synthesize HA. During synthesis, the
reaction was carried out under vigorous stirring at various parameters. As-prepared
HA powders were calcined at different temperatures of 700, 850, 1000 and 1200oC
for 1 hour. The results indicated that high purity HA was obtained and is stable up to
1200oC when the aging time is prolonged to 24 hours. Different concentrations of
reactants, viz. 0.5, 1.0, 1.5 and 2.0 M were also studied. The results indicated that
nano-size HA particles were obtained at all the concentrations whereas pure
stoichiometric HA with high thermal stability of up to 1200oC was obtained at
concentration of 0.5 and 1.0 M.
Based on the optimum conditions which were investigated in the synthesis of
HA, the precipitation method was again employed to synthesize silicon-substituted
HA with silicon contents of 0.4, 0.8 and 1.6% by weight using silicon acetate
[Si(OCOCH3)4] as the Si source. The as-prepared HA and Si-HA powders/pellets
were calcined at different calcination temperatures of 1150, 1200 and 1250oC. The
results showed that pure Si-HA samples were successfully prepared at all three
silicon contents. At all the calcination temperatures, pure Si-HA at silicon content of
0.4 and 1.6 wt% was obtained whilst Si-HA at silicon content of 0.8 wt%
decomposed into รก-TCP at 1250oC. The effect of silicon in HA induced a slight
increase in lattice parameters of apatite structure resulting in slight shifting of XRD
pattern of Si-HA samples. In addition, the silicon in hydroxyapatite inhibited
densification at low temperature (1150oC) and this effect being more significant as
the level of silicon substitution increased. A near-full density (>90%) was achieved
in pure HA at 1200oC whilst the Si-HA sample reached this density at 1250oC. SEM
observation clearly showed that silicon substitution also inhibited grain growth at
high temperatures (1200 and 1250oC). The inhibition of grain growth increased as
the silicon content increased. At a nearly full density, the hardness value of Si-HA
sample reached the comparable value with HA sample. However, higher strength
was achieved in Si-HA samples, and this reached a highest value of 15.93 MPa at
1250oC for sample prepared at 1.6 % of silicon.
Description
Master
Keywords
Materials and Mineral Resources Engineering , Hydroxyapatite , Silicon substituted hydroxyapatite