Surface nucleation apatite

This crystal growth mechanism is linked to surface nucleation. The success-fill application of the mechanisms of surface nucleation and crystallization in the development of cordierite (Semar and Pannhorst, 1991), apatite-wollastonite (Kokubo 1991), and leucite glass-ceramics (Holand et al., 1995a) has already been mentioned in Section 1.4. 

It is interesting to note that the uptake patterns found for Mn2+ on the surface of calcite are similar to those observed for orthophosphate uptake on calcite. Stumm and Leckie (1970) observed a three-stage process for phosphate uptake on calcite surfaces from dilute solutions, representing adsorption, nucleation, and apatite growth. However, deKanel and Morse (1978) found a two-stage pattern of phosphate uptake on calcite from seawater, with an initial rapid adsorption phase followed by slow but steady uptake. 

Apatite - Cas(P04)3X, where X stands for F, OH, and Cl - is usually not found in sediments except where calcite is also present at high concentrations. At marine pH values (7-8), the precipitation of apatite is greatly accelerated by the presence of calcite, the surface of which acts as a nucleating agent for crystallization (topotactic effect). This has been demonstrated by Leckie (1969) and Stumm and Leckie (1970), who also state that in the absence of calcite, high degrees of supersaturation of apatite can be maintained indefinitely. 

Sahai N, Tossell JA (2000) Molecular orbital study of apatite (Ca5(P04)30H) nucleation at sihca bioceramic surfaces. J Phys Chem B 104 4322-4341... 

Self-assembled monolayers terminated with COOH and H2PO4 groups, form bone-like apatite on their surfaces in an SBF [34]. This means that COOH and H2PO4 groups are also effective for apatite nucleation. These functional... 

On the basis of these findings, we can provide a guide for the apatiteforming ability of various materials, that is, not only ceramics, but also metals and organic polymers that posses the functional groups effective for apatite nucleation on their surfaces, and hence we can obtain bioactive materials with different mechanical properties. In the following sections, some examples of these are described. 

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