What is the structural role of magnesium and zinc in silicate glasses?

What is it about?

Magnesium and zinc are key but enigmatic elements in network-forming silicate glasses that have applications in display glass technology and in the immobilization of high-level nuclear waste. Definite information on their structural role is, however, scarce because of the chameleon-like nature of their coordination environments and the experimental challenges that stem from diffraction techniques and element selective spectroscopies. In this paper we address this issue by combining neutron and x-ray diffraction with Raman and solid-state 29Si and 25Mg NMR spectroscopy to investigate the structure of metasilicate composition glasses. No compelling evidence could be found for a network-forming role for the four-coordinated Mg and Zn species.

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Photo by Marek Pavlík on Unsplash

Photo by Marek Pavlík on Unsplash

Why is it important?

The structural role played by magnesium and zinc in silicate glasses is important for elucidating the functional properties of these materials. For example, Zn has been included in some formulations of nuclear waste glass to improve the chemical durability. It was assumed that four-coordinated Zn species act as network formers, thus enhancing the network polymerisation. Instead, we find that four-coordinated Zn species act as network modifiers, an observation that may help to explain why the incorporation of this element, while improving the short-term durability, leads to a degradation in the long-term durability of the glass.

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