Fe-Si Core Research Articles

Thermal and magnetic evolution of Mercury with a layered Fe-Si(-S) core

Elucidating the structure and composition of Mercury is important for understanding its interior dynamics and evolution. The planet is characterised by unusual chemical characteristics and a weak magnetic field generated in a large metallic core, and its early evolution was also marked by the presence of a magnetic field, widespread volcanism and global contraction. Here we develop a parameterised model of coupled core-mantle thermal and magnetic evolution considering a layered Fe-Si(-S) core structure with chemical and physical properties of the mantle and the core based on previous laboratory studies. We seek successful solutions that are consistent with observations of Mercury's long-lived dynamo, total global contraction, present-day crustal thickness, and present-day interior structure. Successful solutions have a mantle reference viscosity >1021 Pa s (corresponding to a present-day bulk mantle viscosity >2×1020 Pa s), a silicon concentration in the core >13 wt%, a present inner core radius of ∼1000−1200 km and a thermally stable layer ∼ 500−800 km thick below the core-mantle boundary. Our results show that if present, a molten FeS layer atop the core has minimal effect on Mercury's long-term thermal and magnetic evolution. Predictions from our models can be tested with upcoming Bepi-Colombo observations.

Crosstalk in an uncompensated gapped-core contactless current transducer

A detailed analysis of the crosstalk in an uncompensated gapped-core current transducer is presented in this paper. A cut-core current transducer with a magnetic field sensor in the airgap is widely used to measure current in industry and in laboratories. Crosstalk is the effect of a nearby current-carrying conductor on the reading of this type of sensor. We present a study of the dependence of the crosstalk on the position of the external conductor, the core material, and the core geometry, including the number of airgaps. A 3D Finite Element Method (FEM) based model is used to analyze the crosstalk, and the results are compared with measurements.Using a low-permeability ferrite core with two 2 mm airgaps and a single Hall sensor results in a maximum crosstalk error of 18 %. This error can be reduced to 1 % either by using a differential Hall sensor pair, or surprisingly by using a single 4 mm airgap. This error can be further reduced to 0.15 % by using an FeSi core with larger permeability. However, this type of sensor is very sensitive to the position of the Hall sensor in the center of the airgap. Displacement or an angular mismatch can increase the error to 1.5 %, as demonstrated on a commercial sensor.

Structure Evolution and Performance of Fe-Si Core Used in Power Inductors of Smart Meters

Structure Evolution and Performance of Fe-Si Core Used in Power Inductors of Smart Meters

High-performance Fe–Si soft magnetic composites with controllable silicate/nano-Fe composite coating

The design of magnetic insulation coating structure has always been a challenge for high-performance soft magnetic composites (SMCs). In this work, we prepared Fe–Si SMCs with silicate/nano-Fe composite coating successfully by in-situ oxidation method combined with spark plasma sintering (SPS). The formation mechanism of the composite coating and its effect on the electro-magnetic properties of Fe–Si SMCs were investigated. The results showed that a uniform Fe2O3 coating can be obtained by reactions between Fe and H2O/O2 during in-situ oxidation process, and became thicker with the increased oxidation time. After sintering, the oxide coating was transformed into a composite coating composed of Fe2SiO4 with excellent insulation and nano-Fe with high ferromagnetism, which resulted from the interfacial reaction between Fe2O3 coating and Fe–Si core. The increased oxidation time led to the gradually thicker composite coating, and resulted in a linear decrease in saturation magnetization, indicating good controllability of the coating. However, excessive oxidation time led to the increased eddy current loss as well as the core loss due to the weakened resistivity. Thus, the Fe–Si SMCs exhibited high saturation magnetic induction (1.66T) and very low core loss (643.9 kW/m3 at 0.1 T/50 kHz) especially when the oxidation time was 1 h.

Adiabatic heat flow in Mercury's core from electrical resistivity measurements of liquid Fe-8.5 wt%Si to 24 GPa

The effect of the core thermal conductivity on the heat flow along the adiabat is investigated using direct measurements of electrical resistivity of Fe8.5Si at pressures from 5-24 GPa and temperatures above melting. Unexpected behaviour at low temperatures between 6-8 GPa may indicate an undocumented phase transition. Measurements of electrical resistivity at melting seem to remain constant at 127 μΩ⋅cm from 10-24 GPa, on both the solid and liquid side of the melting boundary. The adiabatic heat flow at the core side of Mercury's core-mantle boundary is estimated between 21.8-29.5 mWm−2, considerably higher than most models of an Fe-S or Fe-Si core yet similar to models of an Fe core. Comparing these results with thermal evolution models suggests that Mercury's dynamo remained thermally driven up to 0.08-0.22 Gyr, at which point the core became sub-adiabatic and stimulated a change from dominant thermal convection to dominant chemical convection arising from the growth of an inner core.

Use of Bulk Superconductors in the Excitation System of Low-Speed Synchronous Generators

This work focuses on implementing HTS bulks in the excitation circuit of low-speed synchronous generators as permanent magnets. In addition to the implementation study, it is also addressed to remagnetize HTS bulks in electric generators. To reduce the maintenance costs and time required for the magnetization process, an in-loco remagnetization is used. The HTS bulks are magnetized in their position inside the machine's magnetic circuit. A pulse-field magnetization (PFM) technique is used, using the stator coils of a linear generator. YBCO and GdBCO samples are tested. The experimental procedure starts with the in-loco PFM to magnetize the HTS bulks and, by applying an oscillatory movement to the linear generator's moving part, measuring the magnetic flux density induced voltage is done. Experimental tests show that, for the FeSi core used in the generator, the YBCO material is most suitable for the excitation circuit.

No FeS layer in Mercury? Evidence from Ti/Al measured by MESSENGER

In this study we investigate the likeliness of the existence of an iron sulfide layer (FeS matte) at the core-mantle boundary (CMB) of Mercury by comparing new chemical surface data obtained by the X-ray Spectrometer onboard the MESSENGER spacecraft with geochemical models supported by high-pressure experiments under reducing conditions. We present a new data set consisting of 233 Ti/Si measurements, which combined with Al/Si data show that Mercury's surface has a slightly subchondritic Ti/Al ratio of 0.035 ± 0.008. Multiphase equilibria experiments show that at the conditions of Mercury's core formation, Ti is chalcophile but not siderophile, making Ti a useful tracer of sulfide melt formation. We parameterize and use our partitioning data in a model to calculate the relative depletion of Ti in the bulk silicate fraction of Mercury as a function of a putative FeS layer thickness. By comparing the model results and surface elemental data we show that Mercury most likely does not have a FeS layer, and in case it would have one, it would only be a few kilometers thick (<13km). We also show that Mercury's metallic Fe(Si) core cannot contain more than ∼1.5 wt.% sulfur and that the formation of this core under reducing conditions is responsible for the slightly subchondritic Ti/Al ratio of Mercury's surface.

Mercury's thermal evolution controlled by an insulating liquid outermost core?

The weak intrinsic magnetic field of Mercury is intimately tied to the structure and cooling history of its metallic core. Recent constraints about the planet's internal structure suggest the presence of a FeS layer overlying a silicon-bearing core. We performed 4-electrode resistivity experiments on core analogues up to 10 GPa and over wide temperature ranges in order to investigate the insulating properties of core materials. Our results show that the FeS layer is liquid and insulating, and that the electrical resistivity of a miscible Fe-Si(-S) core is comparable to the one of an immiscible Fe-S, Fe-Si core. The difference in electrical resistivity between the FeS-rich layer and the underlying Fe-Si(-S) core is at least 1 log unit at pressure and temperature conditions relevant to Mercury's interior. Estimates of the lower bound of thermal conductivity for FeS and Fe-Si(-S) materials are calculated using the Wiedemann-Franz law. A thick (>40 km) FeS-rich shell is expected to maintain high temperatures across the core, and if temperature in this layer departs from an adiabat, then this might affect the core cooling rate. The presence of a liquid and insulating shell is not inconsistent with a thermally stratified core in Mercury and is likely to impact the generation and sustainability of a magnetic field.

The thermal evolution of Mercury's Fe–Si core

We have studied the thermal and magnetic field evolution of planet Mercury with a core of Fe–Si alloy to assess whether an Fe–Si core matches its present-day partially molten state, Mercury's magnetic field strength, and the observed ancient crustal magnetization. The main advantages of an Fe–Si core, opposed to a previously assumed Fe–S core, are that a Si-bearing core is consistent with the highly reduced nature of Mercury and that no compositional convection is generated upon core solidification, in agreement with magnetic field indications of a stable layer at the top of Mercury's core. This study also present the first implementation of a conductive temperature profile in the core where heat fluxes are sub-adiabatic in a global thermal evolution model.We show that heat migrates from the deep core to the outer part of the core as soon as heat fluxes at the outer core become sub-adiabatic. As a result, the deep core cools throughout Mercury's evolution independent of the temperature evolution at the core-mantle boundary, causing an early start of inner core solidification and magnetic field generation. The conductive layer at the outer core suppresses the rate of core growth after temperature differences between the deep and shallow core are relaxed, such that a magnetic field can be generated until the present. Also, the outer core and mantle operate at higher temperatures than previously thought, which prolongs mantle melting and mantle convection. The results indicate that S is not a necessary ingredient of Mercury's core, bringing bulk compositional models of Mercury more in line with reduced meteorite analogues.

Reduction of Power Transformer Core Noise Generation Due to Magnetostriction-Induced Deformations Using Fully Coupled Finite-Element Modeling Optimization Procedures

This paper focuses on the development of an algorithm for the prediction of transformer core deformation, using a fully coupled magneto-mechanical approach. An imposed magnetic flux method coupled with finite-element modeling is employed for the magnetic resolution. The constitutive law of the material is considered with a simplified multi-scale model describing both magnetic and magnetostrictive anisotropies. Magnetostriction is introduced as an input free strain of a mechanical problem to get the deformation and displacement fields. A 3-D estimation of acoustic power is carried out to evaluate the global core deformation and acoustic noise level. The numerical process is applied to a three-phase transformer made of grain-oriented FeSi core, leading to a set of noise estimation for different flux excitations and core geometries.

Acoustic Noise Characteristics and Magnetostriction of Fe-Si Powder Cores

Fe-Si powder compressed cores have been widely used as reactors in the powder conditioning systems (PCS) of photovoltaic applications and electrical vehicles. Reduction of acoustic noise from the reactor is important when the PCS is installed indoors. In this paper, magnetostriction of the Fe-Si powder cores was investigated in connection with acoustic noise from the reactors assembled with Fe-Si cores. A dummy gage in the coil, wound noninductively, is useful in eliminating the contribution of thermal expansion of cores under strain. Magnetostriction varied with the mechanical strength of the Fe-Si core, which is dependent on the conditions of impregnation. Magnetostriction of the cores was several ppm under the maximum field of 18 kA/m. The Fe-Si cores with lower mechanical strength show lower magnetostriction and thus lower acoustic noise. Strain due to Maxwell force is much larger than that of magnetostriction in the rectangular-type reactor.

Hydrogenation of FeSi under high pressure

Hydrogen is the most abundant element in the solar system, suggesting that hydrogen is one of the plausible light elements in the planetary cores. To investigate the solubility of hydrogen into FeSi and phase relations of the FeSi-H system under high pressure, we performed in situ X-ray diffraction experiments on the FeSi-H and FeSi systems at high pressure and high temperature. Hydrogen starts to dissolve in FeSi (hydrogenation) and form FeSiH x with cubic B20 structure above 10 GPa. Hydrogen content (x), estimated from the volume difference between the FeSi-H and FeSi systems, increases from 0.07 to 0.22 with increasing pressure for P &gt; 10 GPa. Comparing the present results with hydrogenation pressure of Fe, presence of Si in metal increases the minimal pressure for H incorporation. Hydrogen, therefore, can only incorporate into the Fe-Si core at the deeper part (P &gt; 10 GPa) in the planetary interior.

Experimental and modelling analysis of ferroresonant electric circuits

This paper presents a numerical and an experimental investigation on the ferroresonance in a LCR series electric circuit with the aim of deepening the effects of the magnetization phenomena in the ferromagnetic core. In the experiments an Epstein-like FeSi core, enabling an accurate material characterization under the same test conditions, constitutes the non-linear inductance. The model couples the circuit equations with a finite element solution of the one-dimensional electromagnetic field along the lamination thickness. The analysis of the numerical results, which are confirmed by experiments, shows that the accurate prediction of ferroresonance requires the use of detailed constitutive models, when the role of the magnetic losses is significant.

Mössbauer studies in [formula omitted] granular solids

Mössbauer spectroscopy has been used in Fe ( SiO 2, BN) granular solids in order to elucidate the large differences in their coercivity values. The Mössbauer data suggest a core/shell morphology for the Fe SiO 2 films with an Fe(Si) core surrounded by an FeSiO shell whose surface consists of Fe 2+SiO particles. In Fe BN the data indicate the presence of amorphous FeB particles in a BN matrix.

Constraints on core composition from shock-waves data

Seismic data demonstrate that the density of the liquid core is some 8-10 % less than pure iron. Equations of state of Fe-Si, C, FeS 2 , FeS, KFeS 2 and FeO, over the pressure interval 133-364 GPa and a range of possible core temperatures (3500- 5000 K), can be used to place constraints on the cosmochemically plausible light element constituents of the core (Si, C, S, K and O ). The seismically derived density profile allows from 14 to 20 % Si (by mass) in the outer core. The inclusion of Si, or possibly G (up to 11 %), in the core is possible if the Earth accreted inhomogeneously within a region of the solar nebulae in which a C :0 (atomic) ratio of about 1 existed, compared with a G : O ratio of 0.6 for the present solar photosphere. In contrast, homogeneous accretion permits Si, but not C, to enter the core by means of reduction of silicates to metallic Fe-Si core material during the late stages of the accumulation of the Earth. The data from the equation of state for the iron sulphides allow up to 9-13 % S in the core. This composition would provide the entire Earth with a S:Si ratio in the range 0.14-0.3, comparable with meteoritic and cosmic abundances. Shock-wave data for KFeS 2 give little evidence for an electronic phase change from 4s to 3d orbitals, which has been suggested to occur in K, and allow the Earth to store a cosmic abundance of K in the metallic core.

Electronic transformers using amorphous material

An electronic current transformer uses an amorphous material core transformer which operates into a virtually zero ohm load by use of feedback type operational amplifiers. The output voltage is directly proportional to the primary current of the transformer. Due to the very low flux density created by virtually short circuiting the CT, the nonlinear effects and core losses are reduced substantially. An advantage of the electronic transformer is, among others, that a current transformer of reduced size may be used. Application of the amorphous alloys in small electronic current transformers and other devices appear to be justified where the design optimization can make use of (1) the lower cost expected from the amorphous alloys, or (2) their lower losses and higher permeabilities compared to the crystalline Fe-Co and Fe-Si alloys. Test results have shown that the amorphous material core transformer using an active load has somewhat lower performance than Fe-Ni (HyMu 80) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sup> core transformer of the same size but the amorphous core transformer is significantly superior to the Fe-Si core transformer.

Thermal regime in the earth's core and lower mantle

Current views favour the presence of sulphur in the core, giving a composition of Fe + FeS. It is argued that the core composition is close to the eutectic and that this eutectic composition is Fe 2S. The consequences for the thermal regime in the core are examined in terms of the most likely properties of the Fe 2S eutectic. This leads to much lower temperatures than would be expected for an iron or FeSi core. Consideration of the thermal regime in the mantle and the probable thermal properties of lower-mantle assemblages leads to a similar low temperature for the core-mantle boundary. These temperatures require a temperature gradient near the adiabatic in the mantle, implying a convective thermal history.