Precursor decomposition and nucleation kinetics during platelike apatite synthesis.
Self-organization of calcium and phosphorus precursors in solution containing acetic acid and ethylene glycol produces a nanosized lamellar acetate-phosphonate hybrid containing two acetate and one phosphonate components. The lamellar morphology of the hybrid precursor is responsible the formation of platelike apatite product after thermal treatment at or above 400 degrees C. However a preliminary preheating stage (300 degrees C, 24 h) is crucial in determining the morphology of the apatite. Activation energy measurements by nonisothermal thermogravimetric analysis show that decomposition of the hybrid precursor involves at least two steps. Among the three components, it appears that the calcium acetate bidentate chelate component is stable below or at 300 degrees C. However, the calcium phosphonate and calcium acetate monodentate components are decomposed at this temperature. Above 360 degrees C, nuclear magnetic resonance and infrared spectroscopic data reveal the decomposition of more stable calcium acetate bidentate chelate. It is evident that the bond rupture of the bidentate calcium acetate species in the precursor results in the start of crystalline apatite formation but the other components must be decomposed by heating prior to this critical step in order to produce platelike apatite.
Milev
Adriyan S
AS
College of Science, Technology and Environment, University of Western Sydney, Locked Bag 1797, Penrith South DC 1797, Australia. a.milev@uws.edu.au
McCutcheon
Alan
A
Kannangara
G S Kamali
GS
Wilson
Michael A
MA
Bandara
Thilanga Y
TY
D001031:Apatites / Q000138:chemical synthesis*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D013055:Spectrophotometry, Infrared
D001031:Apatites