Dendrimers As Template To Prepare Bio-ceramic Powder Materials

Hydroxyapatite particles precipitated from calcium nitrate and diammonium hydrogenphosphate in the presence of PAMAM are prepared firstly. aggregates of smallcrystallites. The crystallites seem to be self-organized such that they are very wellaligned crystallographically within the volume of the aggregate. The addition ofPAMAM dendrimers with different concentration and generation induces differentparticle sizes and crystallite morphologies. In the absence of dendrimers, aggregatesparticles with a cubic morphology are observed. Increasing the concentration ofdendrimer(PAMAM) added to the precipitating agents induces a variation of theshape from cubes to spherical particles. The crystallites within these particles show amore shorten shape and smaller size as the PAMAM concentration and generation areincreased. The aspect ratio of the PAMAM with NH₂ periphery is decreased greatly,but the those with COO^-periphery is not changed obviously. The polymer additiveseems to influence the three steps of hydroxyapatite precipitation: nucleation,crystallite growth, and aggregation according to the precipitation theory. The presenceof PAMAM affects the hydroxyapatite nucleation step whereby more nuclei arecreated and their sizes decrease as reflected by the crystallite volume (total number ofcrystallites increases while the precipitate yield is constant). In this paper we describethe characterization of these well-organized aggregates and propose a mechanism forthe influence of the PAMAM on the crystallite and aggregate shape firstly. Durningthe preparation of ceramics oxide (ZrO₂,CeO₂, and Y₂O₃) powders with precipitationmethod and hydrothermal method, weekly-agglomerated fine powders were preparedin the presence of PAMAM,but the agglomeration degree is increased in the absenceof PAMAM. Under hydrothermal conditions, the particle size and crystallizationdrgree of ceramic oxides (ZrO₂ and CeO₂) powders increase when the temperature isincreased, when the reaction is increased, the particle size is increased but thecrystallization drgree is changed unobviously.