Combining particle size distribution and isothermal calorimetry data to determine the reaction kinetics of α-tricalcium phosphate–water mixtures

Many calcium phosphate bone substitutes are based on the use of α-tricalcium phosphate (α-TCP) powder. This compound has been intensively studied, but some aspects of α-TCP reactivity are still controversial. The goal of this study was to determine the setting kinetics of α-TCP based on a new approach that compared particle size distribution data to isothermal calorimetry data. Results indicated that α-TCP conversion is mostly controlled by surface reactions, with at later stages a diffusion-controlled mechanism. The presence of an X-ray amorphous α-TCP fraction in the crystalline α-TCP powder increased the dissolution rate threefold, without modifying the reaction mechanism.