KINETICS OF HETEROGENEOUS NUCLEATION OF CALCIUM PHOSPHATES ON ANATASEAND RUTILE SURFACES

The heterogeneous nucleation of calcium phosphates including octacalci um phosphate (Ca4H(PO4)(3). 2.5H(2)O), hydroxyapatite (Ca-5(PO4)(3)OH, HAP), and fluorapatite ((Ca-5(PO4)(3)F, FAP) on anatase and rutile su rfaces has been studied in solutions supersaturated with respect to ea ch phase. Induction periods preceding the initial crystal growth of th e calcium phosphate phases varied markedly with relative supersaturati on, At the same relative supersaturation, the induction time for calci um phosphate nucleation on anatase surfaces was much shorter than that on rutile surfaces. The surface properties of these titanium oxides w ere characterized by zeta-potential measurements and by contact angle measurements involving a thin layer wicking technique. The major diffe rence between the surfaces was in the Lewis base surface tension param eters, gamma(s)(-), 48 and 16 mJ m(-2) for anatase and for rutile, res pectively. (C) 1998 Academic Press.