Synthetic hydroxyapatites (HA) with widely different crystallinity degrees
were prepared starting from calcium hydroxide and phosphoric acid. The powd
ers were carefully characterised by various physico-chemical techniques. Ad
ditions of Ca(OH)(2) were performed in order to improve HA thermal stabilit
y to firing treatments up to temperatures significantly higher than those c
ommonly employed for safe HA sintering. A positive effect in this sense was
found. yielding HA almost purr samples up to 1400-1450 degrees C and maint
aining considerable HA concentrations up to 1600 degrees C. An explanation
in terms of stoichiometric defectiveness, linked to the quantitatively esti
mated contemporary presence of HPO42- and CO32- substituting PO43- and OH-,
was attempted. (C) 2000 Published by Elsevier Science S.A. All rights rese
rved.