Synthetic calcium hydroxyapatite, Ca-10(PO4)(6)(OH)(2) (CaHap), prepared by
a wet method was evacuated at various temperatures up to 900 degrees C and
the influence of thermal treatment on the structure of this material was i
nvestigated by FTIR, determination of concentration of surface P-OH groups,
adsorption of H2O and heat of immersion in water. The number of surface P-
OH groups was 2.6 groups nm(-2) and the ionic ratio of surface HPO42- to H2
PO4- was 31:69. The surface P-OH groups were essentially dehydroxylated by
outgassing above 400 degrees C to produce surface P-O-P species. The heat o
f rehydroxylation per one P-O-P group was determined to be 1.43x10(-16) J g
roup(-1). When outgassed above 600 degrees C, CaHap was rehydrated via the
reaction: (1-x)Ca-10(PO4)(6)(OH)(2)+3x beta-Ca-3(PO4)(2)+xH(2)O --> Ca10-x(
P2O7)(x)(PO4)(6-2x)(OH)(2).