Thermal equation of state and thermodynamic properties of iron carbide Fe 3 C to 31 GPa and 1473 K

Resent experimental and theoretical studies suggested preferential stability of Fe 3 C over Fe 7 C 3 at the condition of the Earth's inner core. Previous studies showed that Fe 3 C remains in an orthorhombic structure with the space group Pnma to 250 GPa, but it undergoes ferromagnetic (FM) to paramagnetic (PM) and PM to nonmagnetic (NM) phase transitions at 6–8 and 55–60 GPa, respectively. These transitions cause uncertainties in the calculation of the thermoelastic and thermodynamic parameters of Fe 3 C at core conditions. In this work we determined P‐V‐T equation of state of Fe 3 C using the multianvil technique and synchrotron radiation at pressures up to 31 GPa and temperatures up to 1473 K. A fit of our P‐V‐T data to a Mie‐Gruneisen‐Debye equation of state produce the following thermoelastic parameters for the PM‐phase of Fe 3 C: V 0  = 154.6 (1) Å 3 , K T 0 = 192 (3) GPa, K T ′ = 4.5 (1), γ 0 = 2.09 (4), θ 0  = 490 (120) К, and q  = −0.1 (3). Optimization of the P‐V‐T data for the PM phase along with existing reference data for thermal expansion and heat capacity using a Kunc‐Einstein equation of state yielded the following parameters: V 0  = 2.327 cm 3 /mol (154.56 Å 3 ), K T 0  = 190.8 GPa, K T ′ = 4.68, Θ E10  = 305 K (which corresponds to θ 0  = 407 K), γ 0  = 2.10, e 0  = 9.2 × 10 −5 K −1 , m  = 4.3, and g  = 0.66 with fixed parameters m E 1  = 3 n  = 12, γ ∞  = 0, β  = 0.3, and a 0  = 0. This formulation allows for calculations of any thermodynamic functions of Fe 3 C versus T and V or versus T and P . Assuming carbon as the sole light element in the inner core, extrapolation of our equation of state of the NM phase of Fe 3 C suggests that 3.3 ± 0.9 wt % С at 5000 К and 2.3 ± 0.8 wt % С at 7000 К matches the density at the inner core boundary. Key Points We present a P‐V‐T EOS for PM‐Fe 3 C with support from thermodynamic analyses We discuss uncertainties in magnetic transitions We applied EOS data for modeling carbon content in the corePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/101805/1/jgrb50396.pd

Editorial for Special Issue “Minerals of Kimberlites: An Insight into Petrogenesis and the Diamond Potential of Deep Mantle Magmas”

Kimberlites are igneous rocks that represent the deepest magmas originated from the mantle (>150 km) and typically occur within cratons [...

40Ar/39Ar Geochronology and New Mineralogical and Geochemical Data from Lamprophyres of Chompolo Field (South Yakutia, Russia)

The alkaline igneous rocks of the Chompolo field (Aldan shield, Siberian craton), previously defined as kimberlites or lamproites, are more correctly classified as low-Ti lamprophyres. The emplacement age of the Ogonek pipe (137.8 ± 1.2 Ma) and the Aldanskaya dike (157.0 ± 1.6 Ma) was obtained using 40Ar/39Ar K-richterite dating. The Chompolo rocks contain abundant xenocrysts of mantle minerals (chromium-rich pyropic garnets, Cr-diopsides, spinels, etc.). The composition of the mantle xenocrysts indicates the predominance of spinel and garnet–spinel lherzolites, while the presence of garnet lherzolites, dunites, harzburgites, and eclogites is minor. The Chompolo rocks are characterized by large-ion lithophile element (LILE) and Light Rare Earth Element (LREE) enrichments, and high field strength element (HFSE) depletions. The rocks of the Ogonek pipe have radiogenic Sr (87Sr/86Sr (t) = 0.70775 and 0.70954), and highly unradiogenic εNd(t) (−20.03 and −20.44) isotopic composition. The trace element and isotopic characteristics of the Chompolo rocks are indicative of the involvement of subducted materials in their ancient enriched lithospheric mantle source. The Chompolo rocks were formed at the stage when the Mesozoic igneous activity was triggered by global tectonic events. The Chompolo field of alkaline magmatism is one of the few available geological objects, which provides the opportunity to investigate the subcontinental lithospheric mantle beneath the south part of the Siberian craton

High-Pressure–High-Temperature Study of Benzene: Refined Crystal Structure and New Phase Diagram up to 8 GPa and 923 K

The high-temperature structural properties of solid benzene were studied at 1.5–8.2 GPa up to melting or decomposition using multianvil apparatus and <i>in situ</i> neutron and X-ray diffraction. The crystal structure of deuterated benzene phase II (<i>P</i>2₁/<i>c</i> unit cell) was refined at 3.6–8.2 GPa and 473–873 K. Our data show a minor temperature effect on the change in the unit cell parameters of deuterated benzene at 7.8–8.2 GPa. At 3.6–4.0 GPa, we observed the deviation of deuterium atoms from the benzene ring plane and minor zigzag deformation of the benzene ring, enhancing with the temperature increase caused by the displacement of benzene molecules and decrease of van der Waals bond length between the π-conjuncted carbon skeleton and the deuterium atom of adjacent molecule. Deformation of benzene molecule at 723–773 K and 3.9–4.0 GPa could be related to the benzene oligomerization at the same conditions. In the pressure range of 1.5–8.2 GPa, benzene decomposition was defined between 773–923 K. Melting was identified at 2.2 GPa and 573 K. Quenched products analyzed by Raman spectroscopy consist of carbonaceous material. The defined benzene phase diagram appears to be consistent with those of naphthalene, pyrene, and coronene at 1.5–8 GPa