Interfacial reactions and silicate formation in high surface SiO_2 impregnated with La nitrate

摘要

Solid state interface reactions in high surface SiO_2 impregnated with lanthanum nitrate were studied at temperature 600-1200 deg C with X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier Transform Infrared spectroscopy (FTIR) and Raman spectroscopy. The results show that at 600-900 deg C an amorphous, nanometer thick La-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. La_6[Si_4O_(13)][SiO_4]_2 silicate forms at temperatures from 950 deg C as the first, quasi two-dimensional phase, and then, at higher temperatures, A-La_2Si_2O_7 silicate occurs. Mechanism of formation of lanthanide silicates in high surface SiO_2 impregnated with Ln nitrates is proposed.