Characteristics of synthetic hydroxyapatites and attempts to improve theirthermal stability

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.