Project
Proton conduction in hydrated silicate glasses

Dr. Harald Behrens
Institute for Mineralogy
University of Hannover, Germany

The project will be performed in close cooperation with Prof. Paul Heitjans and Dr. Sylvio Indris from the Institute of Physical Chemistry and Electrochemistry at University of Hannover.

Ionic conductivity of silicate glasses was studied extensively since several decades. Whereas a broad data base and an increasing knowledge was build up concerning the effect of alkali diffusion on the electrical conductivity of glasses, much less is known on the contribution of hydrous species (H⁺, OH^-). Such species are formed by dissociation of dissolved H₂O in the glasses. Knowledge on migration of protons in silicate glasses and melts is very important for understanding and modelling glass corrosion, proton conduction and hydration/dehydration kinetics. These processes are of great interest for glass technology, geo sciences as well as for archaeology.

In an interdisciplinary project (Mineralogy/Physical Chemistry/Glass science) we want to investigate experimentally the proton conduction of hydrated silicate glasses at temperatures up to 400°C using impedance spectroscopy. At the beginning we want to focus on relatively simple binary and ternary silicates. It is expected that concentration and ionic field strength of network modifying cations have major influence on the electrical conductivity of silicate glasses. Hence, studies with glasses containing various amounts of alkalis (Rb, Cs) and alkaline earths (Ca, Sr, Ba) can provide insights to the mechanism of proton conduction. Comparison of H₂O and D₂O bearing glasses will help to identify the migrating species because the isotope effect is much larger for protons than for hydroxyl groups.

The research involves syntheses of glasses containing several wt% of dissolved H₂O in an internally heated gas pressure vessel at temperatures up to 1500°C and pressures up to 5 kbar. Concentrations of hydrous species as well as hydrogen bonding of these species to neighbouring oxygens will be studied using infrared spectroscopy. Other techniques (¹H NMR spin-lattice relaxation and incoherent neutron scattering) can provide additional information about dynamics of hydrous species in glasses.