European Cells and Materials Vol. 32 Suppl. 7, 2016 (page 49)
ISSN 1473-2262
Correlation between stoichiometry and pH in the wet-chemical synthesis of
calcium orthophosphates
M Habib1, K Hussein1, G Baroud2, N Fatahalla1
1
Mechanical Engineering Department, Al-Azhar University, Cairo, Egypt. 2Laboratoire de
Biomécanique, Université de Sherbrooke, Canada.
INTRODUCTION: Wet process is normally used
for the synthesis of HA, β-TCP or biphasic
calcium-phosphate ceramics HA/TCP through the
following stoichiometric reaction [1, 2]:
NH4OH
X Ca(NO3)2+Y(NH4)2HPO4
[HA]
Ca10(PO4)6(OH)2
X/Y= 1.667
[β-TCP] Ca3(PO4)2
X/Y=1.5
[CDHA] Ca10-x(HPO4)x(PO4)6-x(OH)2-x
1.5<X/Y<1.66, where 0<x< 1
However, the wet process was reported to be less
reproducible on fabrication of pure apatitic TCP in
comparison to other synthesis processes [2]. In this
study, it is hypothesised that a specific apatitic
phase that is normally obtained from stoichometirc
reaction can be synthesised by using nonstoichometric based reactants in a reproducible
way by controlling the pH value during the
synthesis process.
METHODS: (NH4)2HPO4 (Sigma Aldrich,
Germany) and Ca(NO3)2 (Sigma Aldrich, India), as
a starting reactants, were used to produce different
calcium-phosphate phases. The chemical reaction
took place between calcium and phosphorus ions
under controlled temperature (80˚C), stirring time
(2 h) and speed (1450 rpm). The alkalinity of the
reaction was controlled by adding NH4OH
(EDWIC, Egypt). A factorial design with two
factors, three levels and three repeats was
implemented [A: Ca/P (1.5, 1.55, and 1.667) and
B: pH (7.5, 8.5, and 9.5)]. All precipitated powders
were dried and aged overnight and then sintered
for 2 hours at 800 °C. The powders were analysed
for phase, group and elemental analysis by X-Ray
Diffraction (XRD), FTIR, and EDS, respectively.
RESULTS: HA was synthesized at room
temperature, without sintering, from the
sotichometric reaction (Ca/P=1.667) at a controlled
pH of 9.5. Sintering increased the HA crystal size
from 27.28 ± 14.54 nm to 73.35 ± 10.11 nm. βTCP is synthesized stoichiometrically (X/Y=1.5)
and from non-stoichometric based reactants
(X/Y=1.55) at pH of 7.5 (Fig.1). Biphasic Ca/P
with 65% HA and 35% β-TCP can be produced
from stoichometric (X/Y=1.55). Biphasic 45% HA
and 55% β-TCP from non-stoichometric
(X/Y=1.5) based reactants at a controlled pH of 9.5
(Fig.2). FTIR shows that apatitic phase is formed
with the observed fundamental vibrational modes
of PO4 group at 574 and 1020-1120 cm-1. No
impurities were detected in the EDS elemental
analysis (Fig. 1).
C
Fig. 1 XRD of pure β-TCP using A) 1.5, B) 1.55
Ca/P molar ratio and C) EDS elemental analysis
Fig. 2 XRD of biphasic Ca/P using A) 1.5 & B)
1.55 Ca/P molar ratio
DISCUSSION & CONCLUSIONS: The
combined effect of both the reactants Ca/P molar
ratio and pH value was studied. Slight difference in
the reactant molar ratio can affect the synthesised
phases dramatically. However, this slight
difference can be reduced by exactly controlling
the pH value. Sintering temperature is important to
control the crystal size and the phase percentage
when biphasic Ca/P is anticipated.
REFERENCES: 1 S.V. Dorozhkin (2012) Acta
Biomaterialia 8(3):963-977. 2 S. Kannan, A.F.
Lemos and J.M.F. Ferreira (2006) Chem Mater
18(8):2181-2186.
ACKNOWLEDGEMENT: This material is based
on work supported by Bibliotheca Alexandria
BA/CSSP Research Grants-2013.
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