Thermal Treatment of Flame‐Synthesized Amorphous Tricalcium Phosphate Nanoparticles

Flame‐spray synthesis was used to produce nanoparticulate X‐ray amorphous tricalcium phosphate. Upon heating, the material crystallized at temperatures between 525° and 600°C, yielding α‐tricalcium phosphate (TCP) with minor amounts of β‐TCP and hydroxyapatite (HA). Further heating induced a gradual transformation of α‐ to β‐TCP accompanied by crystallite growth and particle fusion. α‐TCP was completely transformed into β‐TCP at 950°C. The high‐temperature polymorph α′‐TCP was not observed. In transmission electron microscopy and selected area electron diffraction analyses, the raw material appeared completely amorphous and samples heated previously to 600° and 700°C comprised single‐crystalline particles of α‐, β‐TCP, and HA. The results of this study demonstrate that nanoparticulate α‐TCP can be obtained from flame‐spray‐synthesized amorphous nanoparticles at temperatures where sintering effects such as particle growth and fusion are moderate, if not negligible.