Crystallization behaviour of a ferri-silicate α-waste glass concluded from Mössbauer spectroscopy

A reference, ferri-silicate α-waste glass containing 10 mole% Fe₂O₃, was thermally annealed at T_a=620, 700 and 800°C, resulting in the formation of crystalline substances. Standard characterization techniques have revealed that the crystal growth is either three-dimensional or rather two-dimensional depending on T_a. The Mössbauer spectra recorded at 80 and ≈=295 K and fitted with a sum of two ferrous and two ferric doublets, do not show any effect doublet areas are found to be consistent with earlier suggestions that in silicate glasses nearly all of the Fe²⁺ ions have an octahedral coordination. The chemical environment of the Fe³⁺ ions in the parent glass seems to remain essentially unchanged upon crystallization, except for the T_a=800°C sample for which the high degree of crystallinity is reflected in a drastic change of the hyperfine parameters. The nature of the crystalline phase, suggested to be diopside-like from diffraction experiments, is discussed. For that purpose. Mössbauer spectra were collected for a synthetic ferri-diopside sample.