What is it about?
The chemical structure of pure molten iron oxides is measured by high-energy synchrotron x-ray diffraction, as a function of oxygen content. This is enabled by aerodynamic levitation of samples combined with laser heating, in a wide range of gaseous atmospheres, from pure oxygen to carbon monoxide-rich CO-CO2 mixtures. It is shown that no existing classical molecular dynamics models are able to fully reproduce the findings, especially the observation of increasing number of chemical bonds per iron (coordination numbers) with oxygen content in the melt. Thus gaps in our knowledge of this important material class are highlighted, pointing toward future research directions.
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Why is it important?
The behavior of iron in molten oxides governs diverse processes from industrial copper smelting slags to natural magma flows. Despite its ubiquitous nature, our research shows we still have an incomplete understanding of how iron behaves, largely due to the complexities inherent with multivalent ions, and the likely need for accurate modelling of the electronic, as well as atomic, structure and properties.
Perspectives
This was part of a major research effort to study multivalent ions in high-temperature melts, as a function of redox via controlling oxygen partial pressure in the surrounding gas. Previous studies involved a combination of x-ray diffraction and Fe K-edge x-ray absorption spectroscopy, mostly on more complex silicate compositions. Whilst the spectroscopic technique is well suited to compositions dilute in Fe, the change in diffraction signal can be subtle and hence compositions rich in Fe are favored, with pure iron oxides representing perhaps the ideal case, and yielding highly informative datasets in the present study.
Dr Oliver Alderman
Science and Technology Facilities Council
Read the Original
This page is a summary of: Redox-structure dependence of molten iron oxides, Communications Materials, November 2020, Springer Science + Business Media,
DOI: 10.1038/s43246-020-00080-4.
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Resources
Teasing Out Iron's Structural Subtleties
Advanced Photon Source Science Highlight of previous work on molten iron silicates.
Local structural variation with oxygen fugacity in Fe2SiO4+x fayalitic iron silicate melts
Previous publication on molten iron silicates.
Iron K-edge X-ray absorption near-edge structure spectroscopy of aerodynamically levitated silicate melts and glasses
Previous paper on spectroscopic studies of iron in melts.
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