Redox-structure dependence of molten iron oxides

Abstract

The atomic structural arrangements of liquid iron oxides affect the thermophysical and thermodynamic properties associated with the steelmaking process and magma flows. Here, the structures of stable and supercooled iron oxide melts have been investigated as a function of oxygen fugacity and temperature, using x-ray diffraction and aerodynamic levitation with laser heating. Total x-ray structure factors and their corresponding pair distribution functions were measured for temperatures ranging from 1973 K in the stable melt, to 1573 K in the deeply supercooled liquid region, over a wide range of oxygen partial pressures. Empirical potential structure refinement yields average Fe–O coordination numbers ranging from ~4.5 to ~5 over the region FeO to Fe2O3, significantly lower than most existing reports. Ferric iron is dominated by FeO4, FeO5 and FeO6 units in the oxygen rich melt. For ferrous iron under reducing conditions FeO4 and FeO5 units dominate, in stark contrast to crystalline FeO.

The structure of molten calcium ferrite under various redox conditions

“…These values were significantly lower than existing data, but are consistent with recent density functional theory calculations [9,21]. Indeed, Shi et al [13] found that in oxygen-rich melts ferric iron is distributed among FeO 4 , FeO 5 and FeO 6 units, whereas under reducing conditions, ferrous iron mostly contains FeO 4 and FeO 5 units.…”

“…The Fe-O coordination environments of iron-bearing silicate melts and glasses have been extensively studied at a variety of compositions and redox conditions by Raman, Mössbauer and X-ray absorption spectroscopies, and total scattering techniques (X-ray and neutron) [13,15,16,[37][38][39][40][41]. A primary theme throughout previous studies has been the concept of 'networkformers' in tetrahedral positions with bridging oxygens and 'network-modifiers' occupying octahedral sites with more non-bridging oxygens, which can have considerable practical importance for the refining of steel.…”

“…It is well known that iron redox can depend on many factors, such as oxygen partial pressure, temperature and composition [13][14][15]. The situation for iron oxide melts is complicated because both ferrous and ferric iron coexist in melts, and exhibit a range of coordination environments.…”

“…Under oxidizing conditions no suitable containers exist, and oxygen pressures of several atmospheres or supercooling are essential to stabilize molten Fe 2 O 3 . In the liquid (FeO) x -(Fe 2 O 3 ) (1−x) system, Shi et al [13] used Empirical Potential Structure Refinement to extract average Fe-O coordination numbers, which ranged from 4.5 to 5 over the region FeO to Fe 2 O 3 . These values were significantly lower than existing data, but are consistent with recent density functional theory calculations [9,21].…”

Nickel -doped iron oxide nanoparticle-conjugated porphyrin interface (porphyrin/Fe2O3@Ni) for the non-enzymatic detection of dopamine from lacrimal fluid

“…5,6 In this context, iron oxide (Fe 2 O 3 ) nanoparticles have gained substantial attention owing to their biocompatibility, nontoxicity, and magnetic accountability along with their remarkable electro-activity and desirable anti-interference characteristics. 7,8 The high ratio of surface oxygen ion mobility in Fe 2 O 3 generates abundant redox-active sites 9 and triggers heterogeneous redox reactions with higher electrocatalytic activity. 10,11 However, Fe 2 O 3 -based interfaces suffer from inherent shortcomings such as agglomeration, heterogeneous distribution and low charge transfer rate with time due to halffilled d-band orbitals, 12 resulting in poor repeatability, storage difficulty and stability.…”