Thermal impurity reactions and structural changes in slightly carbonated hydroxyapatite.

Area of Science:

• Materials Science
• Solid State Chemistry
• Ceramics

Background:

• Slightly carbonated hydroxyapatite (SCHA) is a widely studied biomaterial.
• Understanding impurity effects on SCHA structure and thermal behavior is crucial for its applications.
• Conventional synthesis methods can introduce various impurities into SCHA.

Purpose of the Study:

• To comprehensively study lattice and surface impurity reactions in SCHA.
• To investigate structural changes induced by these impurities upon thermal treatment.
• To elucidate the mechanisms of impurity decomposition and their impact on SCHA structure.

Main Methods:

• Slightly carbonated hydroxyapatite (SCHA) synthesis at 96°C using ammonium-containing reagents.
• Characterization using IR-spectroscopy, X-ray Diffraction (XRD), Thermogravimetric Differential Thermal Analysis (TG-DTA).
• Mass Spectrometric Thermal Analysis (MSTA) for monitoring gaseous decomposition products.

Main Results:

• Identified impurity groups including NH4+, H3O+, CO3(2-), HPO4(2-), H2O, HCO3(-), NO3(-), and NxHy.
• Observed complicated changes in SCHA lattice constants due to impurity reactions during annealing.
• Decarbonation occurred in two stages (450-600°C and 570°C) for A-sites and 700-950°C for B-sites, influenced by impurity reactions.

Conclusions:

• Impurity reactions significantly affect SCHA structure and thermal decomposition behavior.
• Hydrolysis by atmospheric water contributes to hydroxyl ion incorporation above 500°C.
• Sensitive methods like MSTA are essential for accurate analysis of decomposition products in impurity-containing SCHA.