Mechanochemical Synthesis of Fe-Doped Apatite-Type Lanthanum Silicates

Apatite‐type lanthanum silicates (ATLS) doped by Fe were prepared by using mechanical activation, and the effect of the nature of the dopant raw materials on the formation of ATLS was considered. Genesis of the formation of apatite was studied by XRD, IR, HRTEM, and Mössbauer and UV/Vis electron spectroscopy. The possibility of a partial substitution of Si in the apatite with a dopant and the mechanism of formation of ATLS in the course of mechanical activation depend on the dopant parent compound. The structural compatibility of La2O3, La(OH)3, and apatite was shown to favor the rapid formation of apatite‐type silicate by a cluster‐topotactic mechanism during mechanical activation, and the formation of an amorphous ferrosilicate intermediate in the case of the La(NO3)3/SiO2 precursor favors dopant incorporation into the apatite. However, dopant incorporation into the apatite structure was shown to be partially or fully hampered through milling when FeO(OH) and α‐Fe2O3 are used as reagents. Using crystalline hydrates as dopant precursors was shown to result in the formation of apatite through a dissociative mechanism. Rapid formation of apatite‐type silicate by a topotactic acid–base reaction in thecourse of milling is favored by the structural similarities of La2O3, La(OH)3, and apatite, whereas an appreciable amount of water in the reaction space can result in a dissociative mechanism of interaction. Incorporation of a dopant into the apatite during milling involves the intermediate amorphous silicate formation.