Interfacial reactions and silicate formation in highly dispersed Nd2O3–SiO2 system

Solid-state interface reactions in highly dispersed Nd2O3–SiO2 binary oxide system were studied at temperatures 600–1200 °C with X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectroscopy (FTIR). The results show that at 600–900 °C, an amorphous, nanometer thick Nd–O–Si layer covering SiO2 particles exists in the system. At higher temperatures, the breakage of the layer into amorphous islands occurs and crystalline silicates with various structures are formed. In particular, Nd6[Si4O13][SiO4]2 silicate, analogue of recently discovered Ce and La silicates, forms together with well known A-Nd2Si2O7 silicate at temperatures from 950 up to 1100 °C. For samples with high surface coverage (13.6 and 33.3 μmole Nd2O3/1 m2 SiO2), oxyapatite Nd9.33[SiO4]6O2 silicate occurs as intermediate phase at temperatures below 1100 °C. Apparent similarity of an amorphous silicate surface layer to thermodynamically stable disordered nanometer thick films reported recently for Bi2O3–ZnO system is discussed.