Amorphous calcium phosphates synthesized by precipitation from calcium D-gluconate solutions

[Display omitted] ► Preparation of calcium phosphates from non-toxic calcium D-gluconate solutions. ► Rise in crystallinity causes changes in phase composition after thermal treatment. ► β-TCP phase is formed via nanocrystalline hydroxyapatite-like precursor. ► α-TCP is created from phase with high content of amorphous matrix. ► Rise of particle dissagregation to well-ordered nanoclusters with aging time. The amorphous calcium phosphates were synthesized by the precipitation from non-toxic calcium D-gluconate precursor solutions. The low number of nanosized well-ordered calcium deficient hydroxyapatite clusters separated with amorphous calcium phosphate matrix was found at short aging times. The content of intramolecular water in aggregates decreased with an amount of well-ordered clusters and maturation time. The majority α-tricalcium phosphate phase and calcium deficient calcium phosphate were formed after annealing of samples with a high volume fraction of amorphous matrix and nanocrystalline apatite-like phase respectively. The very fine nanocrystalline calcium deficient hydroxyapatite was intermediate phase during thermal transformation to the final β-tricalcium phosphate. The rise of disaggregation of coarse particles to smaller well-ordered hydroxyapatite clusters with aging time was verified. The different amount and size of nanocrystalline clusters were responsible for the formation of various calcium phosphate phases after thermal treatment.