On the Comprehensive Precipitation of Hydroxyapatites Unraveled by a Combined Kinetic-Thermodynamic Approach

The present study combines experimental and theoretical approaches to investigate the competitive precipitation of calcium phosphates (CaPs) in aqueous solution in order to understand and control both the structural and textural properties of the synthesized hydroxyapatites (HAps). Some of the precipitation reactions were followed by in situ Raman spectroscopy or achieved under kinetically controlled conditions. The CaP precursors of HAps were identified as a function of the precipitation pH of the medium and the order of introduction of the precursor ions in the synthesis reactor. Their formation was rationalized by calculations based on a homogeneous nucleation model. Depending on the synthesis conditions, precipitation reaction pathways of HAps are proposed by bringing together the kinetic model developed in the present study and our previous thermodynamic model. HAps are complex materials due to the ease with which large amounts of crystallographic defects, such as carbonates and hydrogen phosphates, can be incorporated in their structure. As these defects play a key role in material sciences (bone substitute, heterogeneous acid-base catalysis, etc.), the present work also includes the analysis of the formation of these crystallographic defects in the apatitic framework, allowing a better control of their incorporation through careful selection of operating parameters.

Automated summary

This study investigates the competitive precipitation of calcium phosphates in aqueous solution through experimental and theoretical approaches. The aim is to understand and control the structural and textural properties of synthesized hydroxyapatites. By analyzing the precipitation pH and the order of introduction of precursor ions in the synthesis reactor, the precursors of hydroxyapatites are identified and rationalized through calculations based on a homogeneous nucleation model. Depending on the synthesis conditions, the precipitation reaction pathways of hydroxyapatites are proposed, and the formation of crystallographic defects in the apatitic framework is analyzed for better control of their incorporation.