Interfacial reactions and silicate formation in highly dispersed Nd 2O 3–SiO 2 system

Abstract

Solid-state interface reactions in highly dispersed Nd 2O 3–SiO 2 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 SiO 2 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, Nd 6[Si 4O 13][SiO 4] 2 silicate, analogue of recently discovered Ce and La silicates, forms together with well known A-Nd 2Si 2O 7 silicate at temperatures from 950 up to 1100 °C. For samples with high surface coverage (13.6 and 33.3 μmole Nd 2O 3/1 m 2 SiO 2), oxyapatite Nd 9.33[SiO 4] 6O 2 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 Bi 2O 3–ZnO system is discussed.