Iron redox effect on the structure and viscosity of silicate glasses and melts
Résumé
The viscosity of silicate melts is one of the most important physical properties for understanding high-temperature phenomena in magmatic systems as well as materials processing. The effects of composition and temperature on viscosity have long been elucidated. Although iron ions are a main component of the magmatic system, their influence on viscosity remains unclear because the behavior of iron is complicated; iron ions have two redox states, that is, Fe 3+ and Fe 2+ . Here, we elucidate the viscosity of an iron-sodium-silicate system with a variety of iron redox states at temperatures close to its glass transition (T g ). The redox states and structures of the samples were characterized using X-ray absorption near-edge structure (XANES) spectroscopy, Raman spectroscopy, synchrotron X-ray total scattering, and density (molar volume) measurements. The viscosity increased (by more than two orders of magnitude) with an increase in the ratio of Fe 3+ to total Fe (Fe 3+ /Fe tot ) whereas the temperature dependence of the viscosity was larger for glasses with a higher Fe 3+ /Fe tot ratio. The tendencies in viscosity and structural variation against the Fe 3+ /Fe tot ratio support the consensus on the structural roles of Fe 3+ and Fe 2+ from previous studies: Fe 3+ ions have a stronger tendency to behave as a network former than Fe 2+ ions.
Mots clés
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