Pure Solid Iron Research Articles

Comparative study on heteropolar/homopolar magnetic bearings for high-speed rotating applications

Bearing technology must be supported to attain high-speed and high-efficiency rotating applications. Previous research focused on performance enhancement and optimization, rather than comparative studies among magnetic bearings. This study presents the design and comparison of five magnetic bearing types for high-speed rotating applications: an 8-pole conventional heteropolar, fork-type heteropolar, hybrid fork-type homopolar, and hybrid homopolar magnetic bearings. For quantitative evaluation, mechanical parameters were selected to ensure a uniform coil volume and current supply. The heteropolar magnetic bearings employed 35PN440 steel, whereas the homopolar magnetic bearings utilized pure solid iron. The bias currents were determined based on the respective material properties. The driving circuits were compared by comparing models with and without permanent magnets. The magnetic flux density was assessed at equilibrium and maximum control current, and the loss characteristics were evaluated at 30 000 rpm. Linear control regions were identified by analyzing the relationships between the electromagnetic force, current, and displacement. As a result, the most suitable magnetic bearing for high-speed rotating applications is proposed.

Partitioning of silicon and sulfur between solid and liquid iron under core pressures: Constraints on Earth's core composition

Not only the Earth's outer core but also the inner core contains light elements, which causes reductions in density and velocity with respect to those of pure solid iron. Silicon, sulfur, and possibly hydrogen are believed to be important inner core light elements, because their partition coefficients between solid Fe and liquid, D (solid/liquid), are high (>0.7) under inner core pressures unlike other possible light elements such as oxygen and carbon. Recent experiments demonstrated that DSi is remarkably enhanced with increasing sulfur concentration in liquid at 15–21 GPa. Here we conducted solid/liquid partitioning experiments on the Fe-Si-S(-C) system up to the Earth's core pressure range of 189 GPa in a laser-heated diamond-anvil cell (DAC) and examined the effect of silicon-sulfur interaction on both DSi and DS. The results show that DS significantly diminishes with increasing the silicon content in liquid, while DSi increases with higher sulfur concentration. Based on these partitioning data, we explored the pairs of possible liquid outer core and solid inner core compositions in the Fe-Si-S±H±O system, which account for their respective seismological observations of the density and velocities. For the temperature at the inner core boundary of 5400 K, we obtained Fe + Ni + 2.7–3.0 wt% Si + 1.7 wt% S (fixed) + 0.32–0.59 wt% H + 0.05–2.5 wt% O for the outer core and Fe + Ni + 2.5–2.8 wt% Si + 0.69–0.70 wt% S + 0.23–0.43 wt% H for the inner core.

Phosphate Capacities of CaO–FeO–SiO2–Al2O3/Na2O/TiO2 Slags

Abstract To effectively increase the dephosphorization efficiency of hot metals or the previous stage in the converter steelmaking process, phosphate capacities ( C P O 4 3 − ) {\rm{(}}{{\rm{C}}_{{\rm{PO}}_4^{3 - }}}) of CaO–FeO–SiO2–Al2O3/Na2O/TiO2 slags at 1300–1400°C were examined by laboratory experiments using equilibrating slag and pure solid iron foil. The data suggested that ( C P O 4 3 − ) {\rm{(}}{{\rm{C}}_{{\rm{PO}}_4^{3 - }}}) increases with decreasing temperature and increasing slag basicity. Compared to basicity, temperature considerably affected the phosphate capacities and tended to be the most important factor. The phosphate capacities of slag considerably decreased at a high temperature of 1400°C even under high binary basicity as well as high contents of Na2O and FeO. Moreover, with the increase in the content of FeO and Al2O3 in the slag, ( C P O 4 3 − ) {\rm{(}}{{\rm{C}}_{{\rm{PO}}_4^{3 - }}}) decreased. A low content of Na2O led to the increase in the phosphate capacities of slag, particularly at low temperatures of 1300–1350°C. The content of TiO2 in the slag considerably exhibited a weaker effect on ( C P O 4 3 − ) {\rm{(}}{{\rm{C}}_{{\rm{PO}}_4^{3 - }}}) . Furthermore, by regression analysis, ( C P O 4 3 − ) {\rm{(}}{{\rm{C}}_{{\rm{PO}}_4^{3 - }}}) was expressed as a function of the temperature and slag compositions as follows: logC PO 4 3 − = 0.041 ( % CaO ) − 0.086 log ( % FeO ) − 0.024 ( % SiO 2 ) − 0.02 ( % Al 2 O 3 ) + 0.067 ( % Na 2 O ) + 0.039 ( % TiO 2 ) + 56767 / T − 14.58 , ( R = 0.978 ) \eqalign{&{{\rm{log}}{{\rm{C}}_{{\rm PO}_4^{3 - }} = 0.041( \% {\rm CaO}) - 0.086{\rm log}({\rm{ \% }}{\rm FeO})} - 0.024( \% {\rm Si{O_2}})} \cr &{{ - 0.02({\rm{ \% }}{\rm A{l_2}{O_3})}} { + 0.067( \% {\rm N{a_2}O)} + 0.039( \% {\rm Ti{O_2})}}} \cr &+ 56767/{\rm T} - 14.58, ({\rm R} = 0.978)}}

Saturation of electrical resistivity of solid iron at Earth's core conditions.

We report on the temperature dependence of the electrical resistivity of solid iron at high pressure, up to and including conditions likely to be found at the centre of the Earth. We have extended some of the calculations of the resistivities of pure solid iron we recently performed at Earth’s core conditions (Pozzo et al. in Earth Planet Sci Lett 393:159–164, 2014) to lower temperature. We show that at low temperature the resistivity increases linearly with temperature, and saturates at high temperature. This saturation effect is well known as the Mott-Ioffe-Regel limit in metals, but has been largely ignored to estimate the resistivity of iron at Earth’s core conditions. Recent experiments (Gomi et al. in Phys Earth Planet Int 224:88–103, 2013) coupled new high pressure data and saturation to predict the resitivity of iron and iron alloys at Earth’s core conditions, and reported values up to three times lower than previous estimates, confirming recent first principles calculations (de Koker et al. in Proc Natl Acad Sci 109:4070–4073, 2012; Pozzo et al. in Nature 485:355–358, 2012, Phys Rev B 87:014110-10, 2013, Earth Planet Sci Lett 393:159–164, 2014; Davies et al. in Nat Geosci 8:678–685, 2015). The present results support the saturation effect idea.

Melting of Fe–Ni–Si and Fe–Ni–S alloys at megabar pressures: implications for the core–mantle boundary temperature

High pressure melting behavior of three Fe-alloys containing 5 wt% Ni and (1) 10 wt% Si, (2) 15 wt% Si or (3) 12 wt% S was investigated up to megabar pressures by in situ X-ray diffraction and laser-heated diamond anvil cell techniques. We observe a decrease in melting temperature with increasing Si content over the entire investigated pressure range. This trend is used to discuss the melting curve of pure Fe. Moreover, our measurements of eutectic melting in the Fe–Fe3S system show a change in slope around 50 GPa concomitant with the fcc–hcp phase transition in pure solid iron. Extrapolations of our melting curve up to the core–mantle boundary pressure yield values of 3,600–3,750 K for the freezing temperature of plausible outer core compositions.

The identity and quantity of the light matter on each side of the Earth's inner core boundary

Light elements in the iron-rich core of the Earth are important indicators for the evolution and dynamics of our planet. However, there is a longstanding controversy surrounding the identity and quantity of the light elements. The theory of tricritical phenomena has been recently employed as a precise theoretical framework to study solidification at the high pressures and temperatures of the Earth. When combined with the most reliable iron melting data and the seismic data, the theory provides the solidification temperature at the inner core boundary (ICB) pressure for both pure iron and for the alloy of iron and light elements in the actual core melt. Here the theory is used further to find a value of about 5 mol.% for the amount of light matter in the core melt at ICB and to calculate the density of liquid pure iron at its melting temperature. These give the density of the light matter consistent with it being MgSiO 3, and this identification is supported by sound velocity against density analysis. In addition, using the pure iron density and volume contraction obtained from the same theory, one finds the density of pure solid iron at its melting temperature. The sound velocity against density analysis for different iron crystal structures and various light compounds possibly present in the solid at the ICB shows that the most likely structure here is iron in its bcc δ phase with 4 wt.% Mg 2SiO 4 as light impurity. This finding is close to the conclusion of recent shear velocity calculations for Fe with Mg. The light matter identified here challenges the commonly assumed exclusion of mantle material in the core and this issue is discussed.

Activities of Phosphorus in Copper‐Iron Liquid Alloys Saturated with Copper‐Iron Solid Solutions

In order to determine the activities of phosphorus and iron in liquid {Cu‐Fe‐P} alloys, the two coexisting phases of liquid {Cu‐Fe‐P} alloys + <Cu‐Fe‐P> solid solutions were brought into equilibrium with a mixture of Al2O3 + AlPO4 + FexAl2O4 at temperatures of 1416K and 1526K. The oxygen partial pressures were measured with the aid of a solid‐oxide galvanic cell of the type:(+)Mo / Mo + MoO2/ ZrO2(MgO) / {Cu‐Fe‐P} + <Cu‐Fe‐P> + <Al2O3> + <AlPO4> + <FeAl2O4> / Fe(‐)The equilibrium reactions underlying the experiments can be expressed by 2[P]cu + (5/2) (O2) + <Al2O3> = 2 <AlPO4> and x[Fe]Cu + (1/2) (O2) + <Al2O3> = <FexAl2O4>The Henrian activity coefficient referred to 1 wt pct solution in pure liquid copper could be well expressed by the formulalog fP° = (4.46±0.40) ‐ (8.67±0.59)/(T/K).The iron activities referred to pure solid iron could be formulated as log aFe =‐ (0.37 ± 0.12) + (500 ±200) /(T/K).

Nitrogen Dissociation Rate at Solid Surface of Ferrous Alloys.

The nitrogen dissociation rates at the surface of solid iron-M (M: Si, Al, Mn, Cr, and Ti) alloys have been measured by an isotope exchange technique at temperatures ranging from 1 473 to 1 798 K. From the present results, the rate constant of nitrogen dissociation at the surface of pure solid iron is derived as 1.97×10 -5 [mol/(cm 2 .s.atm)] at 1 773 K and the apparent activation energies for the nitrogen dissociation at the surfaces of δ-Fe and γ-Fe ([mass ppm O]=10.3, [mass ppm S]=7) at P N2 =0.05 (atm) are calculated as 127 and 162 (kJ/mol), respectively. The effects of the alloying elements on the nitrogen dissociation rate at the surface of solid iron have the same tendency as those at the surface of liquid iron investigated previously by a similar method to the present study; the nitrogen dissociation rate is increased by the addition of Mn, Cr, or Ti and is decreased by the addition of Si or Al. The degree of the effects of increasing or decreasing the rate by the alloying elements for the solid iron is found to be smaller than that for the liquid iron.

Thermodynamic study of Fe-Ta and Fe-Nb alloys by means of the Knudsen cell mass spectrometry.

The activity of iron in the Fe–Ta and Fe–Nb alloys at 1 873 K was determined by means of the Knudsen cell mass spectrometry. A modified internal standard method was employed, in which a piece of pure iron foil placed on the sample surface in the Knudsen cell served as the internal standard material. The ion intensity of iron from the foil was first measured at several temperatures before the alloy sample and the foil melted together. The ion intensity from pure solid iron thus obtained was extrapolated to give ion intensity from pure liquid iron at higher temperatures. The temperature of the sample was then raised to form uniform liquid alloy and the ion intensity of iron from the alloy was measured. The activity of iron in the alloy was determined by comparing the ion intensities from pure iron and from alloy.The activities of Ta and Nb were derived from that of iron by integrating the Gibbs-Duhem equation. The activity coefficients of Ta and Nb in the infinitely dilute solution with liquid pure metal as the standard state were also calculated. The interaction parameters were determined. These results were compared with those of elements adjacent to Ta and Nb in the periodic table.Invariant reactions appeared in the Fe–Ta binary alloy system at high temperature were investigated by employing the ion intensity thermal analysis, in which the ion intensity represented the temperature of the sample. Heat treatment and metallographic study was also carried out for the identification and composition determination of phases.

Thermodynamics of Ca-CaF2 and Ca-CaCI2 systems for the dephosphorization of steel

Calcium is soluble in halide salts which can be used to remove phosphorus from steel as a phosphide ion. The activity and activity coefficient of calcium phosphide, and the equilibrium phosphorus distribution ratio between Ca-CaF2 and Ca-CaCl2 fluxes and pure solid iron were measured as a function of the Ca composition in the flux at 1350 °, 1400 °, and 1450 °. The Ca-Ca halide fluxes were equilibrated with pure solid iron and a Ag-Ca alloy in an iron crucible under an Ar atmosphere. The Ag-Ca alloy was used to maintain a constant chemical potential of calcium. Phosphorus distribution between between these fluxes and solid pure iron increased with increasing calcium activity and decreasing temperature. The activity coefficient of γCa 1.5 P was calculated to be 36.6 at 1350 ° and 11.0 at 1450 ° for a calcium activity of 0.2 (wt pct Ca = 2.5) in the Ca-CaF2; the activity coefficient increases with increasing Ca in the flux. In addition, the activity of Ca in the Ca-Ca halide fluxes was determined. The equilibrium phosphorus distribution ratio between Ca-Ca halide systems and molten chromium steel was calculated as functions of Cr and C contents of the metal and calcium activity in the flux at 1600 °C by using γCa 1.5 P obtained in the present work. This ratio was found to be about 20 for 18 pct Cr stainless steel at 1600 °.

The Earth's core and the phase diagram of iron

The phase diagram of iron is presented for P < 330 GPa. The melting curve is derived from Stevenson’s generalized form of Lindemann’s law, successfully connecting the low-pressure (5-20 GPa) measurements to the new shock-wave measurements of 250 GPa. The isothermal equation of state of e-iron (h.c.p.) and y-iron (f.c.c.), indicate that the inner core density is that of pure solid iron. The present experiments cannot distinguish between the e or y phase for the inner core, but preference is given to y-iron. From these constructions, it is concluded that the melting temperature of iron at the inner core - outer core boundary pressure, T (i.c.b.), is 5200-6600 K. A likely model of the outer core temperature is presented by taking 5800 K as the probable value of T (i.c.b.), and assuming a temperature drop of 1000 K due to chemically induced melting point depression. This yields 3620 K for the T of the core side of the core-mantle boundary (c.m.b.). This model results in a large AjT(D"), (700 K), at the c.m.b., but the shock-wave data also allow other models where A!T(D") is less. A numerical experiment reveals that the value for A T(D") of 700 K does not lead to distortion of the density profile. The (y-8-liquid) triple point is beyond the i.c.b. Thus, diluted y-iron in the liquid phase constitutes the outer core. The experiments support a thermally driven model of the geomagnetic dynamo, and further support a model of a slowly freezing inner core for the energy source.