Magnesiowustite Research Articles

Ab initio lattice thermal conductivity of (Mg,Fe)O ferropericlase at the Earth’s lower mantle pressure and temperature

The effects of iron (Fe) incorporation on the lattice thermal conductivity () of MgO are investigated under the Earth’s lower mantle pressure (P) and temperature (T) condition (P > ∼20 GPa, T > ∼2000 K) based on the density-functional theory combined with the anharmonic lattice dynamics theory. The of ferropericlase (FP) is determined combining the internally consistent LDA + U method and self-consistent approach to solve the phonon Boltzmann transport equation. The calculated are well fitted to the extended Slack model which is proposed in this study to represent in a wide volume and T range. Results demonstrate that the of MgO decreases strongly by Fe incorporation. This strong negative effect is found due to decreases in phonon group velocity and lifetime. Consequently, the of MgO at the core-mantle boundary condition (P∼ 136 GPa, T ∼ 4000 K) is substantially reduced from ∼40 to ∼10 W m−1 K−1 by the incorporation of Fe (12.5 mol%). The effect of Fe incorporation on the of MgO is found to be insensitive to P and T, and at high T, the of FP obeys a well-established T inverse relation unlike the experimental observations.

Effect of temperature on the slag/refractory interfacial reaction with directed reduced iron (DRI) addition in an electric arc furnace (EAF) process: Diffusional growth of magnesiowüstite layer by Boltzmann-Matano analysis

This study investigated the effect of temperature (1550–1650 °C) on the electric arc furnace (EAF) slag and magnesia refractory interfacial reaction with 20% direct reduced iron (DRI) addition as an alternative iron source in an Ar atmosphere. Variations in MgO content from initial to final stage were proportional to the temperature, indicating that MgO degradation by molten EAF slag was affected by the concentration gradient between initial and saturation conditions depending on temperature. In addition, the temperature affected MgO content more dominantly than DRI did. In other words, temperature control in an EAF process using DRI is relatively more important than the control of DRI itself for preventing MgO refractory degradation. The magnesiowüstite (MW) intermediate layer thickness and MgO refractory dissolution depth increased as the temperature increased because MgO solubility in molten EAF slag is proportional to temperature. Finally, the inter-diffusivity (D˜Fe−Mg, m2/s), which was estimated by Boltzmann-Matano analysis, ranged D˜Fe−Mg=10−12.0−10−12.5 and logD˜Fe−Mg generally decreased with decreasing temperature. The activation energy was found to be approximately 240 kJ/mol. Therefore, it can be concluded that suitable control of temperature in an EAF process using DRI is important to minimize refractory degradation.

Interfacial reactions between magnesia refractory and electric arc furnace (EAF) slag with use of direct reduced iron (DRI) as raw material

Interfacial reactions between the electric arc furnace (EAF) slag, i.e., CaO–SiO 2 –FeO–MgO–Al 2 O 3 –MnO system, and the magnesia refractory as a function of direct reduced iron (DRI) addition (0, 10, 20, 30 wt%) were investigated at 1550 °C under an Ar atmosphere. MgO solubility increases with increasing DRI content by decreasing basicity (i.e., CaO/SiO 2 ratio), which is due to an increase in SiO 2 supplied from DRI. The measured MgO content was always lower than the theoretical MgO saturation level irrespective of DRI content because the magnesiowüstite (MW) intermediate layer, which formed at the slag/refractory interface, retarded the direct dissolution of the refractory by acting as a self-protective layer. The thickness of the MW intermediate layer and dissolution depth were proportional to DRI content. However, the penetrativity decreased with increasing DRI content by decreasing the fluidity of the slag. Several kinetic parameters were estimated, including the dissolution rate constant of the MW intermediate layer, the dissolution rate of the MgO refractory, and the rate constant of MW growth. Dissolution of MgO refractory is controlled by the dissolution of the MW intermediate layer. Increasing the growth rate is very important for protecting refractory after the formation of a MW intermediate layer. In addition, we provided a schematic diagram of the slag/refractory interfacial reaction phenomena that compares situations of low and high DRI content. The results of the present study show that it is necessary to control DRI content to minimize refractory degradation during the EAF process. If a large amount of DRI must be used in the EAF process, then MgO content in the slag should be at the saturation limit at first, which accelerates growth of the MW intermediate layer.

Mechanism of magnetic moment collapse under pressure in ferropericlase

We propose a new scenario for the magnetic collapse under pressure in ferropericlase (FP) ()O without the presence of intermediate spin state, which contradicts the mechanism proposed in (2013 Phys. Rev. B 87 165113). This scenario is supported by results of combined local density approximation + dynamical mean-field theory method calculations for the paramagnetic phase at ambient and high pressures. At ambient pressure, calculation gave ()O as an insulator with Fe 3d-shell in high-spin state. Experimentally observed high-spin to low-spin state transition of the ion in the pressure range of 35–75 GPa is successfully reproduced in our calculations. The spin crossover is characterized by coexistence of ions in high and low spin state but intermediate spin state is absent in the whole pressure range. Moreover, the probability of Fe ion configuration with grows with pressure due to shortening of metal–oxygen distance. Also, no metal–insulator transition was obtained up to the pressure 140 GPa in agreement with experiment.

Stability of (Mg0.5Fe0.5)O and (Mg0.8Fe0.2)O magnesiowüstites in the lower mantle

We have heated magnesiowustites (Mg 0.5 Fe 0.5 )O and (Mg 0.8 Fe 0.2 )O to temperatures of over 1000 K at pressures of over 80 GPa simulating the stability of the solid solution at physical conditions relevant to the Earth9s lower mantle. The X-ray study of the externally heated samples in diamond-anvil cells shows that magnesiowustite may dissociate into a magnesium-rich and an iron-rich oxide component. The result is important because the decomposition of magnesiowustite into lighter and heavier phases will cause dynamic effects that could lead to mantle heterogeneity.

Dynamic behavior of superparamagnetic iso-oriented magnesioferrite nanoparticles

Small magnetic particle systems generally present complex magnetic behaviors, which are due to the similarity of effects arising from distribution of size, shape, orientation of anisotropy axis and interparticle interactions that can jeopardize the comparison between experimental results and theoretical models. The system formed by magnesioferrite (MgFe 2O 4) nanoparticles precipitated in dilute solid solutions of iron in MgO (magnesiowüstite) is interesting since the insulating single crystal matrix impose nanoparticles iso-orientation, and the interparticle interactions are negligible. In addition it is easy to change its average particle size by sample annealing. In this work, we present some dynamic magnetic properties of this system and its relation with the evolution of the average particle sizes with annealing time.

Fe–Mg partitioning between post-perovskite and magnesiowustite

Fe–Mg partitioning between post-perovskite and magnesiowustite

Thermoelastic properties of (Mg 0.64Fe 0.36)O ferropericlase based on in situ X-ray diffraction to 26.7 GPa and 2173 K

We present 53 in situ measurements of the unit-cell volume ( V) of polycrystalline (Mg 0.64Fe 0.36)O ferropericlase (FP) at simultaneous high pressures ( P) and temperatures ( T) up to P = 26.7 GPa and T = 2173 K, including pressure–temperature conditions at the top of Earth's lower mantle. FP volumes were determined through in situ energy-dispersive synchrotron X-ray diffraction in a multi-anvil press, using gold and MgO as pressure markers. Our data, combined with 112 previously published P– V– T measurements for the same FP sample, were fitted to high-temperature Birch-Murnaghan and Mie-Grüneisen equations of state (EOS). Experimental data are reproduced accurately, with a standard deviation lower than 0.31 GPa for both EOS. EOS calculations show that the thermal expansion and P– T derivatives of the bulk modulus of this iron-rich FP are virtually identical to those of pure MgO to pressures >55 GPa and temperatures of 3000 K. This result is confirmed by measurements of the normalised unit-cell volumes for FP and MgO at identical simultaneous high P– T conditions, which are identical to within 0.6 per cent relative to 26.7 GPa and 2173 K. The pressure and temperature derivatives of the bulk modulus, and thermal expansion are concluded to be independent of iron content across the range of plausible FP compositions in Earth's lower mantle.

Thermal expansivity in the lower mantle

The pressure dependence of the thermal expansion coefficient, α, previously reported as (∂lnα/∂lnV)T = 5.5 ± 0.5 by Chopelas and Boehler [1989] is refined, using systematics in the volume dependence of (∂T/∂P)s measured for a large number of materials at high pressures and high temperatures. Since (∂ln (∂T/∂P)s/∂(V/V0))T is found to be constant and material independent over a very large compression range, (∂lnα/∂lnV)T is proportional to the compression, V/V0. We find α decreases by a factor of 5 for MgO throughout the mantle, reaching a value of 1.0 · 10−5 K−1 at its bottom. Densities of perovskite (PV) and magnesiowüstite (MW) are calculated for lower mantle conditions using our new α(P, T), a room temperature finite strain equation, and recent data on the Mg‐Fe partitioning in the PV‐MW system. Both minerals have nearly identical densities to those of PREM throughout the entire lower mantle, which allows variable PV:MW ratios. A lower mantle made entirely of PV with a molar ratio of Mg:Fe of 88:12 would be about 0.11 g/cm3 or 2.5% denser than this mixture, but this density would just be within the uncertainty in PREM. A change in chemistry at 660 km depth to a PV mantle requires a thermal boundary which would improve the match in the densities between PV and PREM. These density agreements therefore preclude evaluation of a mineralogical model for the lower mantle using density comparisons. Recent measurements on melting of Fe, FeO, and FeS, however, suggest temperatures at the core‐mantle boundary below 3500 K, which tends to favor a geotherm without a large thermal boundary at 660 km depth.

MgO飽和CaO-MgO-FeO<SUB>x</SUB>-SiO<SUB>2</SUB>系スラグ-溶鉄間のりん分配

Experiments have been made to study the phosphorus distribution between liquid iron and the CaO-MgO-FeOx-SiO2 slag equilibrated in a magnesia crucible in the temperature range 1 550-1 650°C. The phosphorus distribution ratio (P2O5)/[P] increased with increasing CaO content and decreasing temperature. The maximum values of the distribution ratio were found to be present near the slag composition saturated with the tricalcium silicate and the magnesio wustite phases. The experimentally determined phosphorus content in metal disagreed with the phosphorus content estimated from the treatments proposed by Balajiva et al., Turkdogan and Pearson, and Healy over the present range of slag compositions, except by Flood and Grjotheim.

Phosphorus distribution between liquid iron and MgO saturated slags of the system CaO-MgO-FeOx-SiO2.

Experiments have been made to study the phosphorus distribution between liquid iron and the CaO-SiO2-FeOx slag equilibrated in a magnesia crucible in the temperature range 1550° to 1650°C. The phosphorus distribution ratio (P2O5)/[P] increased with increasing CaO content and decreasing temperature. The maximum value of the distribution ratio was found to be present near the slag composition saturated with the tricalcium silicate and the magnesio wustite phases. The experimentally determined phosphorus content in metal disagrees with the phosphorus contents estimated from the treatments proposed by Balajiva et al., Turkdogan and Pearson, and Healy over the present range of slag compositions, except by Flood and Grjotheim.