Neutron Laue diffraction study of the complex low-temperature magnetic behaviour of brownmillerite-type Ca2Fe2O5

Mechanistic study on the promotion of Ca2+ leaching in steel slag through high-temperature solid waste modification

Indirect carbonation of steel slag is an effective method for CO2 storage, reducing emissions, and promoting cleaner production in the steel industry. However, challenges remain, such as low Ca2+ leaching rates and slag management complexities arising from variations in mineral compositions. To address this, a high-temperature modification process is proposed to alter the mineral composition and facilitate the synergistic utilization of calcium and iron. This study delves into the effects of various solid waste modifications on the leaching of Ca2+ and the total iron content within steel slag. Results show that high-basicity modified slag forms Ca2(Al, Fe)2O5, reducing calcium leaching. Low-alkalinity modified slag produces calcium-rich aluminum minerals and also reduces the leaching of Ca2+ ions. At a basicity of 2.5, coal gangue, fly ash, and blast slag achieve maximum Ca2+ leaching rates of 88.93%, 89.46%, and 90.17%, respectively, with corresponding total iron contents of 41.46%, 37.72%, and 35.29%. Upgraded coal gangue exhibits a 50.02% increase in calcium leaching and a 15.58% increase in total iron content compared to the original slag. This enhances CO2 fixation and iron resource utilization. Overall, the proposed indirect carbonation and iron enrichment modification offer a novel approach for the resource utilization and environmental stability of steel slag.

Reversible Exsolution of Dopant Improves the Performance of Ca2Fe2O5 for Chemical Looping Hydrogen Production

Hydrogen (H₂) is a clean energy carrier and a major industrial feedstock, e.g., to produce ammonia and methanol. High-purity H₂ can be produced efficiently from methane (CH₄) using chemical looping-based approaches. In this work, we report on the development of a calcium-iron-based oxygen carrier (Ca₂Fe₂O₅) doped with Ni or Cu and investigate its redox performance for H₂ production when CH₄ is used as the fuel. The experimental results suggest that the rapid formation of metallic Ni or Cu through exsolution promotes the reducibility of Ca₂Fe₂O₅ with CH₄. It was found that the reversible exsolution of Ni or Cu nanoparticles and their reincorporation in the Ca₂Fe₂O₅ structure is key to avoid particle sintering and deactivation. Having the potential of converting a larger fraction of steam to H₂ than pure iron oxide in addition to its higher reactivity with CH₄, the doped calcium-iron-based oxygen carrier is a promising material for chemical looping H₂ production.

Spatially Confined Spin Polarization and magnetic sublattice control in (La,Sr)MnO3-δ Thin Films by Oxygen Vacancy Ordering

Perovskite oxides are known for their strong structure property coupling and functional properties such as ferromagntism, ferroelectricity and high temperature superconductivity. While the effect of ordered cation vacancies on functional properties have been much studied, the possibility of tuning the functionality through anion vacancy ordering has received much less attention. Oxygen vacancies in ferromagnetic La_0.7Sr_0.3MnO_3−δ thin films have recently been shown to accumulate close to interfaces and form a brownmillerite structure (ABO_2.5). This structure has alternating oxygen octahedral and tetrahedral layers along the stacking direction, making it a basis for a family of ordered anion defect controlled materials. We use density functional theory to study how structure and properties depend on oxygen stoichiometry, relying on a block-by-block approach by including additional octahedral layers in-between each tetrahedral layer. It is found that the magnetic and electronic structures follow the layers enforced by the ordered oxygen vacancies. This results in spatially confined electronic conduction in the octahedral layers, and decoupling of the magnetic sub-lattices in the octahedral and tetrahedral layers. These results demonstrate that anion defect engineering is a promising tool to tune the properties of functional oxides, adding a new avenue for developing functional oxide device technology.

Weak ferromagnetic ordering in brownmillerite Ca2Fe2O5 and its effect on electric field gradients

Electric field gradients in weakly ferromagnetic CaFe₂O₅ remarkably change below T_N, because of local electric polarizations induced by Dzyalosinskii-Moriya interactions.