The understanding of how macromocules act in precipitation of inorganic phases is the key knowledge that is needed to establish the foundation to mimic nature and produce materials with high mechanical modulus besides Outstanding optical and thermal properties. This study investigated how addition of small amounts of alginate (7-70 ppm), that presents many carboxylic groups, affects phase distribution and morphology of calcium phosphates, obtained through precipitation and further submitted to calcination and sintering. The results lead to the Conclusion that alginate action is dynamic, where alginate molecules act as templates to nucleation, and most of the biopolymer remains in solution even when all calcium phosphate has precipitated. However, despite the effect on phase composition being mainly related to the system's kinetics, alginate does present thermodynamic interaction with the precipitates. It is probable that it acts by reducing the free energy Of nucleation, as in heterogeneous nucleation processes. (C) 2008 Elsevier B.V. All rights reserved.29411091113