P-V-T measurements of Fe3C to 117 GPa and 2100 K: Implications for stability of Fe3C phase at core c
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McGuire, Chris↗
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Materials Data on Fe3C by Materials Project
Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations
36 MATERIALS SCIENCE↗
Materials Data on Fe11MoC4 by Materials Project
MoFe5C2(Fe3C)2 crystallizes in the monoclinic Pm space group. The structure is two-dimensional and consists of one Fe3C sheet oriented in the (0, 1, 0) direction and one MoFe5C2 sheet oriented in the (0, 1, 0) direction. In the Fe3C sheet, there are four inequivalent Fe sites. In the first Fe site, Fe is bonded in a single-bond geometry to one C atom. The Fe–C bond length is 1.79 Å. In the second Fe site, Fe is bonded in a single-bond geometry to one C atom. The Fe–C bond length is 1.88 Å. In the third Fe site, Fe is bonded in a square co-planar geometry to four C atoms. There are two shorter (2.01 Å) and two longer (2.04 Å) Fe–C bond lengths. In the fourth Fe site, Fe is bonded in a square co-planar geometry to four C atoms. There are a spread of Fe–C bond distances ranging from 1.99–2.04 Å. There are two inequivalent C sites. In the first C site, C is bonded to six Fe atoms to form a mixture of corner and edge-sharing CFe6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the second C site, C is bonded to six Fe atoms to form a mixture of corner and edge-sharing CFe6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the MoFe5C2 sheet, Mo is bonded in a square co-planar geometry to four C atoms. There are a spread of Mo–C bond distances ranging from 2.10–2.12 Å. There are three inequivalent Fe sites. In the first Fe site, Fe is bonded in a single-bond geometry to one C atom. The Fe–C bond length is 1.89 Å. In the second Fe site, Fe is bonded in a single-bond geometry to one C atom. The Fe–C bond length is 1.90 Å. In the third Fe site, Fe is bonded in a square co-planar geometry to four C atoms. There are a spread of Fe–C bond distances ranging from 1.92–1.95 Å. There are two inequivalent C sites. In the first C site, C is bonded to two equivalent Mo and four Fe atoms to form a mixture of corner and edge-sharing CFe4Mo2 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the second C site, C is bonded to two equivalent Mo and four Fe atoms to form a mixture of corner and edge-sharing CFe4Mo2 octahedra. The corner-sharing octahedra tilt angles range from 0–1°.
36 MATERIALS SCIENCE↗
Laboratory infrared spectra of predicted condensates in carbon-rich stars
Laboratory spectra and mass absorption coefficients of MgS, CaS, FeS, SiS2, FeS2, Fe3C, and a commercial iron carbide are presented over the wavelength range 125-15 microns. These spectra confirm that MgS is the most likely source of the unidentified 30-micron emission in carbon-rich sources and that FeS, Fe3C, and 'iron carbide' cannot be responsible for this feature although they could contribute to the continuum in this region. CaS and FeS2 may contribute to the 30-micron feature; however, both higher resolution and higher precision astronomical observations are needed before their presence can be established. SiS2 has a peak near 22 microns and therefore cannot be a significant component of the dust in such regions.
Nuth, J. A.↗
The iron spin transition of deep nitrogen-bearing mineral Fe3N1.2 at high pressure
Abstract Nitrogen is an essential element for life, one of the most abundant volatiles in the atmosphere, and an important component in the Earth’s interior, where iron nitride is an essential host of deep nitrogen. Here, we investigate the pressure-induced electronic spin-pairing transition of iron in siderazot (Fe3N1.2) at pressures up to 45.8 GPa at room temperature, using diamond-anvil cell techniques coupled with synchrotron X-ray emission spectroscopy. The integrated intensity of the satellite emission peak (K′β) decreases upon compression but remains unchanged at pressures greater than 30.5 GPa. In other words, the high-spin to low-spin transition of iron in Fe3N1.2 starts immediately at very low pressures and completes at ~30.5 GPa. The iron spin transition completion pressures increase with the nitrogen concentration of hexagonal close-packed iron nitrides (i.e., Fe3N1.2, Fe7N3, and Fe2N). Moreover, the identity and concentration of light elements in binary iron-rich compounds such as Fe3N, Fe3C, Fe3P, Fe3S, Fe7C3, and Fe7N3, together with their crystal structure, could affect the iron spin transition pressures. The spin transition of iron-rich alloys could alter the bonding nature and the physical properties, including the thermal and electrical conductivity, thereby influencing the thermal state and evolution of planetary interiors.
Geochemistry & Geophysics↗
Electronic Structure and Spin Correlations in Novel Magnetic Structures
The research has advanced understanding of the interrelation between the crystal structure and magnetism in several materials which are or can be of interest for the development of improved, specialized or more cost-effective permanent magnets, as well as in selected materials for biomedical and catalytic applications. Fundamental aspects of ferromagnetism were investigated for Mn-Ge, Co-V and Co-Ge nanoclusters and for melt-spun Co-Sn alloys. New solution-chemistry synthesis methods were designed and tested for Fe-Pt, Fe3C and Fe3O4 nanoparticles. Off-stoichiometric Laves phases in the Fe-Si-Zr, Fe-Nb and Fe-Ta systems, as well as Fe5(Si,Ge)B2 compounds were assessed as new rare-earth-free permanent magnet materials; all except the Fe-Si-Zr Laves phases were found to be promising enough to merit a further exploration. A new method for manufacturing rare-earth-free magnets based on the MnBi compound was developed; by purposely avoiding oxidation-sensitive fine single-crystalline powders, the new method yields magnets with a 50% larger energy storage capacity. Studies of rare-earth-lean permanent-magnet materials (lean compared to the currently predominant Nd-Fe-B materials) were focused on the tetragonal compound of the ThMn12 structure type and included both discovery and characterization of new formulations and exploration of new fabrication/processing techniques. Among the most significant achievements were successful preparation of a vanadium-lean SmFe11V compound, the first observation of thermomechanically induced texture in nanocrystalline Sm(Fe,V)12 alloys, and a breakthrough reduction-diffusion synthesis of Sm1-xZrx(Fe0.8Co0.2)11.2Ti0.8 single-crystal particles with a coercivity as high as 12.6 kOe. Several experiments aimed at improvement of the Nd-Fe-B magnet have also been undertaken including a five-fold increase of the coercivity through a grain-boundary diffusion treatment of a Nd10Fe84B6 nanocrystalline alloy.
36 MATERIALS SCIENCE↗
The effect of C/O ratio on the condensation of planetary material
The condensation temperatures of refractory silicates and oxides in a gas of cosmic composition are strongly dependent on the C/O ratio. As the ratio increases from 0.4 to 0.9, condensation temperatures of compounds such as Al2O3, Ca2Al2SiO7, MgAl2O4, Mg2SiO4, and MgSiO3 decrease by 50-100 degrees. As C/O increases from 0.9 to 1.0, these temperatures drop an additional 300-400 degrees. Other chemical differences result when C/O approximately equals or exceeds 0.9. A new suite of high-temperature minerals appears (graphite, CaS, Fe3C, SiC and TiN); the reaction CO + 3H2 yields CH4 + H2O proceeds to the right at higher temperatures; and iron, whose condensation temperature is unaffected, condenses at higher temperatures than any silicate or oxide.
Larimer, J. W.↗
Iron and the formation of astrophysical dust grains
Condensation of metallic iron or the iron carbide cohenite Fe3C is proposed as the source of the approximately 1000 K dust condensate in nova shells, Wolf-Rayet stars, and other objects. Iron grains may serve as nucleation sites for carbon in carbon-star ejecta; however, nucleation of graphite at its equilibrium saturation temperature is almost certainly kinetically inhibited. A gas phase rich in CO, C2H2, and HCN is produced instead.
Lewis, J. S.↗
Intermediate phases in some rare earth-ruthenium systems
The phase equilibria and crystal structures of intermediate phases were investigated in eight representative RE-Ru systems using powder X-ray diffraction and metallographic techniques. The Fe3C, Mn5C2 and Er5Ru3 structures occur in all but the Ce-Ru systems. Phases analogous to Er5Ru3 possess an unknown crystal structure similar to Er5Rh3(I). MgCu2 and MgZn2 type Laves phases are encountered in the light rare earth and heavy rare earth systems, respectively, and RERu2 phases, where RE = Nd and Sm, possess both the Laves phase structures. An intermediate phase, NdRu, with an unknown structure, occurs only in the Nd-Ru system. A bcc structure with 40 atoms per unit cell is encountered in the phases Er3Ru2 and Y3Ru2. The behavior of cerium in Ce-Ru alloys is unique in that four unidentified structures, not encountered in other RE-Ru systems, have been encountered. Also a phase designated as Ce3Ru is found with the Th7Fe3 type structure.
Sharifrazi, P.↗
A New Analytical Approach to Predict Spacing Selection in Lamellar and Rod Eutectic Systems
The Jackson and Hunt (JH) theory has been modified to relax the assumption of isothermal solid/liquid interface(SLI) used in their treatment. Based on the predictions of this modified theory the traditional definitions of regular and irregular eutectics are revised. For regular eutectics the new model identifies a range of spacing within the limits defined by the minimum undercooling of the alpha and beta phase. For the irregular Al-Si eutectic system two different spacing selection mechanisms were identified: a) for a particular growth rate, a nearly isothermal interface can be achieved at a unique minimum spacing lambda(sub I); b) the average spacing (lambda(sub av) greater than lambda(sub I)) is essentially dictated by the undercooling of the faceted phase. Based on the modified theoretical model a semiempirical expression has been developed to account for the influence of the temperature gradient, which is dominant in the irregular Al-Si system. The behavior of the Fe-Fe3C eutectic is also discussed The theoretical calculations have been found to be in good agreement with the published experimental measurements.
Catalina, Adrian V.↗
A New Analytical Approach to Predict Spacing Selection in Lamellar and Rod Eutectic Systems
The Jackson and Hunt (JH) theory has been modified to relax the assumption of isothermal solid liquid interface used in their treatment. Based on the predictions of this modified theory, the traditional definitions of regular and irregular eutectics are revised. For regular eutectics, the new model identifies a range of spacing within the limits defined by the minimum undercooling of the a and beta phases. For the irregular Al-Si eutectic system, two different spacing selection mechanisms were identified: (1) for a particular growth rate, a nearly isothermal interface can be achieved at a unique minimum spacing lambda (sub t); (2) the average spacing (lambda (sub av) greater than lambda (sub t) is essentially dictated by the undercooling of the faceted phase. Based on the modified theoretical model, a semiempirical expression has been developed to account for the influence of the temperature gradient, which is dominant in the irregular Al-Si system. The behavior of the Fe-Fe3C eutectic is also discussed. The theoretical calculations have been found to be in good agreement with the published experimental measurements.
Catalina, Adrian V.↗
First Report of Taenite in an Asteroidal Interplanetary Dust Particle: Flash-heating Simulates Nebular Dust Evolution
Metallic iron with a taenite structure rimmed by Fe3C carbide, kamacite with a magnetite rim, both approximately 200 nm in size, and les than 15 nm kamacite crystals embedded in equilibrated aggregates (or GEMS) were reported in IDPs. Here I report the first g-(Fe,Ni), taenite, in sulfide fragment -F6 particle with adhered patches of thermally modified aggregate IDP-like material belonging to cluster IDP L2011#21.
Rietmeijer, F. J. M.↗
Laser pyrolysis fabrication of ferromagnetic gamma'-Fe4N and FeC nanoparticles
Using the laser pyrolysis method, single phase gamma'-Fe4N nanoparticles were prepared by a two step method involving preparation of nanoscale iron oxide and a subsequent gas-solid nitridation reaction. Single phase Fe3C and Fe7C3 could be prepared by laser pyrolysis from Fe(CO)5 and 3C2H4 directly. Characterization techniques such as XRD, TEM and vibrating sample magnetometer were used to measure phase structure, particle size and magnetic properties of these nanoscale nitride and carbide particles. c2000 American Journal of Physics.
NASA Discipline Life Sciences Technologies↗
The Formation of Carbonaceous Material in the Early Solar Nebula: The Role of Metal Dusting
For many years it has been suggested that the carbonaceous material found in association with Fe/Ni metal and metal carbides in primitive bodies is linked to the Fischer–Tropsch reaction. This is especially true with chondritic-porous interplanetary dust particles, which are considered to have a cometary origin and are among some of the most primitive and least processed materials available for study. Another phenomenon which occurs under the same carburizing conditions as the Fischer–Tropsch reaction is called metal dusting and could be a possible pathway to forming some of the carbonaceous material found in primitive bodies. Metal dusting is a catastrophic corrosion of metal under these carburizing conditions that results in a porous mixture of carbonaceous material, metal, and metal carbides. In the case of pure iron, type I metal dusting results in the formation of a metastable iron carbide, typically cementite, Fe3C. While metal dusting has been studied industrially for over 50 years, it does not appear to have been applied to the formation of carbonaceous material in astrophysical settings. In this work, the general mechanism of metal dusting on iron is described and a thermodynamic analysis of the dusting phenomena applied to solar nebula conditions. Rate measurements are made with pure iron samples over the temperature range from 400°C to 950°C. In addition, the products from experimental runs at 500°C and 600°C are studied by transmission electron microscopy. Results show that iron carbide particles are formed with carbonaceous material consisting of poorly graphitized carbon.
Interplanetary dust↗