Modelling the Zn environment in simple and complex glasses using EXAFS

N.J. Cassingham*, N.C. Hyatt and P.A. Bingham
University of Sheffield

It has been suggested documented that zinc increases the durability of oxide glasses; however, the environment of zinc in these glasses is not fully understood. In order to understand the mechanisms by which zinc increases glass durability, simple and complex silicate glasses with additions of zinc were used to probe the zinc environment using X-ray absorption spectroscopy (XAS). The three glasses analyzed were a sodium zinc silicate, a simulated nuclear waste borosilicate glass, and corroded zinc doped nuclear waste borosilicate glass. XAS data of the sodium zinc silicate glass (NZS) was used to create a model for fitting a simple glass analogous to the crystal (Na2ZnSi3O8). The model created from fitting the NZS glass was used to gain insight on the Zn environment in the complex glasses used for vitrification of nuclear waste. The model for fitting the zinc environment in a simple glass resulted in the ability to model the complex glasses without the knowledge of the co-ordination around zinc. Single scattering paths and multiple scattering paths were used during modelling resulting in the most acceptable fits and the co-ordination of zinc was found to be tetrahedral in all three samples. Only using single scattering paths while modelling the zinc environment yields acceptable results; however, the fits improve when multiple scattering paths are used. The ability to model the zinc environment in each of the glasses to 3.5Å suggests intermediate range order around zinc in a zinc alkali (boro) silicate glass.