Alpha-tricalcium phosphate synthesized by two different routes: Structural and spectroscopic characterization

In the present study two alpha-tricalcium phosphate powders (αTCP-1 and αTCP-2) were synthesized by slightly different routes. For structural comparison, commercial pure α-TCP (αTCP-st) was used. The influence of the preparation method on physicochemical properties of α-TCP was investigated using scanning electron microscopy (SEM) and powder X-ray diffraction (PXRD). The chemical structure of the samples was determined using spectroscopic methods: mid-infrared spectroscopy (FT-IR), Raman spectroscopy and solid-state nuclear magnetic resonance (ssNMR). Specific surface area of the synthesized αTCP-1, αTCP-2 and standard αTCP-st powders was measured using the BET method with nitrogen adsorption. The studies have shown differences in morphology of the samples. αTCP-1 is characterized by small grains forming agglomerates below 2 µm while the αTCP-2 powder has a tendency to form compact clusters with micropores below 5 µm. Its specific surface area is about 5 times lower than αTCP-1 and close to the reference material. PXRD demonstrated that αTCP-1 is significantly less crystalline. In addition, the crystallinity of αTCP-2 was comparable to that of the standard sample. FT-IR and ssNMR experiments have indicated that αTCP-1 is not homogenous but contains beside alpha-tricalcium phosphate amorphous calcium phosphate (ACP). We suggest that ACP may be found in the interior of agglomerates and therefore it is not converted to a highly crystalline form at higher temperature. Different ways of grinding and heat treatment strongly influence characteristic properties (crystallinity, Ca/P molar ratio, phase composition, specific surface area) of the obtained αTCP.