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The conduction of heat through minerals and melts at extreme pressures and temperatures is of central importance to the evolution and dynamics of planets. In the cooling Earth's core, the [...]

The effect of iron on the post-perovskite phase transition has been controversial. We have performed direct chemical analyses of co-existing perovskite and post-perovskite that were synthesized from an ([Mg.sub.0.91][Fe.sub.0.09])Si[O.sub.3] bulk composition using a laser-heated diamond anvil cell at pressures above 100 GPa and temperatures of 1700-1800 K. Analysis on quenched samples was carried out using the transmission electron microscope (TEM). The results demonstrate that crystalline perovskite grains are enriched in iron compared to adjacent amorphous parts presumably converted from post-perovskite. This indicates that ferrous iron stabilizes perovskite to higher pressures. The ferrous and ferric irons are likely to have competing effects on the post-perovskite phase transition, and therefore the effect of iron may be controlled by aluminum. Keywords: Perovskite, post-perovskite, iron partitioning, phase transition, D' layer

The oxidation state of Fe in hydrous ultrapotassic (phono-tephritic) melts coexisting with mixed [H.sub.2]O-C[O.sub.2] fluids was studied experimentally at 1200 and 1250[degrees]C and pressures from 50 to 500 MPa. The oxygen fugacity ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) varied from NNO-2.9 to NNO+2.6 in log [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], relative to the Ni-NiO oxygen buffer (NNO), as imposed by external redox conditions in experimental vessels and internal variations in water activity from 0.05 to 1 inside the capsules. The Fe redox state of the quenched melts was determined by colorimetric wet-chemical analysis. This analytical method was optimized to measure the [Fe.sup.2+]/[SIGMA]Fe ratio of milligram-sized samples within [+ or -] 0.03 (2[sigma]). The accuracy and precision was tested with international reference materials and with standards analyzed by other methods. The [Fe.sup.2+][SIGMA]Fe ratio of the experimental glasses covered a range of 0.41 to 0.85. A small negative effect of dissolved water on [Fe.sup.2+]/[SIGMA]Fe at given [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] was found, consistent with the thermodynamic model of Moretti (2005). No effect of pressure and temperature on the redox state of Fe was resolvable in the investigated P-T range. Compared to hydrous ferrobasaltic melts that were studied previously under similar conditions, systematically lower [Fe.sup.2+]/[SIGMA]Fe ratios were found for the phono-tephritic melts, in particular at low oxygen fugacities. This effect is attributed to the much higher [K.sub.2]O contents of the phono-tephrite (7.5 compared to 0.3 wt%), but the difference in Fe[O.sub.T] (7.8 wt% in the phono-tephrite and 12.9 wt% in the ferrobasalt) may have an influence as well. Comparison of the experimentally obtained relationship between log [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and [Fe.sup.3+]/[Fe.sup.2+] for the studied hydrous ultrapotassic melts with commonly used empirical and thermodynamic models suggest that these models can be successfully applied to phono-tephritc melts, although such compositions were not implemented in the model calibrations. Furthermore, the new data can be used to improve the models with respect to the effects of compositional variables, such as [H.sup.2]O or [K.sub.2]O, on the redox state of Fe in silicate melts. Keywords: Fe oxidation state, FeO determination, oxygen fugacity, water activity, phono-tephrite, ultrapotassic hydrous silicate melt, Alban Hills

A constitutive model is developed in this work to describe the mechanical behavior of body centered cubic metals under a wide range of strain rates and temperatures. The model is based on macromechanical state variables such as stress, strain, and material constants that include threshold and transition temperature as well as micromechanical terms such as mobile dislocation density and burgers vector. The principle of the activation energy and its dependence on temperature, strain rate, and stress is the key point in this proposed model. The model is used to simulate the experimental behavior of pure iron at various temperatures and strain rates in order to obtain the different model parameters. The model shows good capability in capturing the coupling between strain rate and temperature, plastic strain and strain rate, and plastic strain and temperature. The model is used to characterize the hardness of iron at low and high strain rates for a representative strain of 8%. CE Database subject headings: Constitutive models; Strain rate; Temperature; Iron.

A study was conducted to experimentally investigate the two-dimensional expansion and the elliptical temperatures of several laser-induced plasmas (LIPs) produced during the ablation of metallic samples. A weak LIP, both in terms of temperature and in terms of forward peaking is observed to be associated with the ablation of Al, while a hot and dynamic LIP is produced during the ablation of a low boiling point material such as Zn with significant angular spread and high temperature.

Various studies are employed to study the kinetics and thermodynamics of the synthesis and characterization of an iron(III) (Fe(III)) complex of a novel crown ether-porphyrin conjugate, in addition to several other hydroxo, dimeric and peroxo species. The analysis demonstrates the reversible binding of the superoxide to the metal center, which normally occurs as a result of the fine-tuning of the proton concentration due to the specific physiological conditions.

A study is carried out on the Fe nanofluids that are prepared with ethylene glycol and Fe nanocrystalline powder synthesized by a chemical vapor condensation process. The results shows that the thermal conductivity of a Fe nanofluid is increased nonlinearly up to 18% as the volume fraction of particles increases up to 0.55 vol.%.

The preparation of structure and stability of an iron-based catalyst for the oxygen reduction reaction by heat treatment of carbon-supported iron(III) tetramethoxyphenylporphyrin chloride are investigated. A degradation by H2O2, which is a by product of the oxygen reduction, can explain the decrease of catalytic activity during longevity tests.

It is found by Mossbauer measurements on [M.sub.0.025][Fe.sub.0.975]S (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) that the 3-D-transition metal impurities profoundly affect both the structural phase and the spin rotation transitions of iron sulfide. It is noteworthy that both [V.sub.0.025][Fe.sub.0.975]S and [Co.sub.0.025][Fe.sub.0.975]S have Morin transition temperatures [T.sub.M] which are distinctly different from that of FeS; furthermore, the directions of changes of [T.sub.M] are opposite for [V.sub.0.025][Fe.sub.0.975]S and [Co.sub.0.025][Fe.sub.0.975]S. A vanadium impurity of 2.5 % of the metal atoms in the iron sulfide makes the structure transition take place rapidly in a narrow temperature region of about 15 K, while the [alpha] transition in FeS takes place over a wide temperature range of about 200 K. It is also found that the [alpha] transition for [V.sub.0.025][Fe.sub.0.975] S has a hysteresis width of 5 K. It is noteworthy that the structural transition is independent of the lattice parameters while the spin-rotation transition is dependent on them. Index Terms--[M.sub.0.025][Fe.sub.0.975]S(M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu), phase transition, spin-rotation, 3-D-transition metal.

The thermal transport properties such as thermal conductivity and thermal diffusivity for the mentioned samples have been discussed by comparison with those foe other candidates as the magnetic refrigerants working in the vicinity* of room temperature such as Gd5Si2Ge2, Gd and MnAs.

The preparation, as well as the electrical properties exhibited by the polyethylene glycol nanofluids containing carbon coated metal nanoparticles is analyzed. The thermal conductivity of the system is shown to be increase significantly with an increase in the filter loading frequency.

Several studies are conducted to explain the magnetic anisotropy, as well as the hyperthermia properties of the various small Fe nanoparticles present in the superparamagnetic regime. The specific absorption rate of these nanoparticles is shown to be completely dependent on their magnetic field.

Nickel zinc ferrite (NZFO) nanoparticles are prepared by using a reverse micelle method with a nonionic surfactant. Three different initial [Fe.sup.3+]/[Fe.sup.2+] ratios are used along with three different firing temperatures to examine the effects on the NZFO system and the extended x-ray absorption fine structure results have disclosed zinc loss at high annealing temperatures.

The successful applications of a simple coagulation model adapted from the theory of aerosol formation in the modeling of the production of iron nanoparticles are described. The recquired experimental conditions and factors to increase the production of large particle-size nanomaterials as function of particle size are also described.

The framework of the spherical random-bond-random-field model for the relaxor ferroelectric sublattice and the Heisenberg model for the magnetic sublattice was considered to study the influence of cation substitution on the Curie temperature and the magnetocapacitance in the doped magnetic relaxor ferroelectrics Cd[Cr.sub.2][S.sub.4]. The results revealed that the value of the Curie temperature increased significantly by A-site substitution of the Cd by Fe in [Cd.sub.1-x][Fe.sub.x][Cr.sub.2][S.sub.4] and the doping Fe ions play a critical role in the fluctuation of spin-pair correlation and magnetocapacitive response.

A study is conducted to examine the effect of Fe substitution on the phase transformation and magnetic properties of [Mn.sub.2]NiGa. Theoretical calculations indicated that both austenitic and martensitic phases are ferrimagnets and the Fe moment which varies from positive to negative after the tetragonal distortion leads to the decrease of the saturation magnetization.

The electron transport for Fe-doped diamond-like carbon (DLC) thin films on Si substrate was studied at different temperatures and voltages. The three-stage I-t curve process not observed in the nondoped DLC/Si system could be elucidated in terms of the electric-field-induced [sp.sup.3]-to-[sp.sup.2] conversion, in which embedded Fe works as catalyst.

Spin-polarized density functional theory calculations are performed to explore the carbon pathways and hydrogenation mechanism for C[H.sub.4] formation on [Fe.sub.2]C(011), [Fe.sub.5][C.sub.2](010), [Fe.sub.3]C(001), and [Fe.sub.4]C(100). The calculated reaction energies and effective barriers revealed the C[H.sub.4] formation to be more favorable on [Fe.sub.5][C.sub.2](010) and [Fe.sub.2]C(011), while [Fe.sub.4]C(100) and [Fe.sub.3]C(001) are inactive toward C[H.sub.4] formation.

The preparation of iron and copper nanoparticle-based thermal fluids prepared by using a two-step process is described. The studies have shown that the thermal conductivity can be increased for copper nanofluids and for a given particle concentration, copper nanofluids are superior in thermal conductivity when compared to iron nanofluids.

Diffuse reflectivity is used for examining the effect of hydrostatic pressure on the thermal spin transition of Fe[(PM-BiA).sub.2][(NCS).sub.2] polymorph I (PM = N-2-pyridylmethylene and BiA = 4-aminobiphenyl). The studies have shown the onset of a progressive transformation into a phase of higher cooperativity that cannot be assigned to polymorph II.

The shock response of polycrystalline iron is studied in a series of planar impact experiments by using interferometer monitoring of the free surface of preheated/precooled samples. The dynamic yield and tensile strengths of iron are determined over the 143-1275 K temperature range, which is based on the recorded waveforms.

The single-turnover-like reaction conditions at ?78 degree [Celsius] are used to obtain a new dark-brown species with ([[lambda].sub.max] = 396, 732, 843 nm) from dark-green ([[lambda].max] = 440, 611, 747 nm) complex of iron(III) meso-N-substituted corrole ([TBP.sub.8]Cz)[Fe.sup.III] ([TBP.sub.8]Cz = octakis(4-tert-butylphenyl)corrolazinato). Rapid-mixing stopped-flow UV-vis studies showed that the low-temperature dark-brown complex is generated as a short-lived intermediate at room temperature and EPR spectroscopic characterization established the complex as an antiferromagnetically coupled iron(IV)-oxo [pi]-cation-radical complex.

The monoenergetic positron annihilation and photoluminescence (PL) measurements are used to study the thermal stability of SI property in Fe-doped GaN (GaN:Fe) films fabricated by hydride vapor phase epitaxy. The results for the defect chemistry of films indicated the possible use of GaN:Fe as a thermally stable SI substrate for electronic devices as its surface does not decompose during the epitaxial growths of overlayers.

[Co.sub.0.8][Mn.sub.x][Fe.sub.2.2-x][O.sub.4] (x = 0.2, 0.4, 0.6, and 0.8) powders are prepared by a sol-gel process and annealed at different temperatures and magnetic and structural properties are measured. The decrease in coercivity ([H.sub.c]) is attributed to the content decrease in [Co.sup.2+] on B sites and increasing grain sizes at higher annealing temperature have an intensive influence on [H.sub.c].

The isothermal oxidation of two iron-cobalt based alloys is examined. X-ray diffraction measurements have displayed the presence of MO-[Fe.sub.2][O.sub.3]-type (where M = Co, Nb, V) spinel structures along with [Fe.sub.2][O.sub.3].

Mossbauer investigation has shown that the highest value of saturation magnetization is achieved in [Ni.sub.0.65][Zn.sub.0.35][Fe.sub.2][O.sub.4] at lower sintering temperatures through sol-gel synthesis. Cation distribution of the composition is proposed and verified by calculating the intensity of each peak of x-ray diffraction and estimating the lattice constant.

The low temperature electrical transport properties of the carbon matrix containing iron nanoparticles and the films are comparatively studied. The films have displayed a crossover of the conductivity from power-law dependence at high temperatures to activated hopping law dependence in the low temperature region, which is attributed to changes in the energy dependence of the density of states near the Fermi level.

The amorphous (a-) CoFeB/crystalline (c-) MgO based tunneling system interface is studied by using a quantitative high resolution electron microscopy from atomic to micrometer length scales with increasing annealing temperatures. On the atomic scale a long-range is induced by the MgO interface, which has described the high tunnel magnetoresistance values >100% even for not fully crystallized CoFeB/MgO/CoFeB tunnel junctions.

The grazing incidence x-ray fluorescence method has differentiated the terrestrial contamination from the low concentration implanted solar wind. The elemental depth distribution is obtained by using this method, which has resulted in the determination of absolute solar wind elemental abundance.

Interfacial microstructure modulation is shown in [Ni.sub.80][Fe.sub.20]/(Ni,Fe)O thin films, where different ion bombardment energies have changed the exchange coupling between the (Ni,Fe)O and [Ni.sub.80][Fe.sub.20 interfaces. One interface configuration has provided positive or negative exchange coupling depending on whether the film is cooled with or without an external magnetic field, while another interface configuration has resulted in the more typical negative exchange coupling independent of the field cooling.

The characterization of a high-temperature (2000 K) thermal gas aggregation source which is ultrahigh vacuum compatible and could cleanly deposit transition metal clusters with partial pressures of contaminants in the 10-11 mbar range to facilitate codeposition with highly reactive matrices is described. The mass spectra of Fe clusters produced and recorded via the use of a quadrupole filter showed that a wide range of cluster sizes could be produced by changing the operating conditions and configuration of the source.

A study was conducted to explore the magnetization reversal mechanism in elliptical shaped nanomagnets obtained from single layer and pseudospin valve [Co.sub.50][Fe.sub.50] films. The magnetization reversal process of the single layer elements is strongly dependent on the film thickness and the strength of the coupling is significantly dependent on temperature.

A series of AlCrCoNiFe based alloys with equal percentage of principal components is fabricated and the related crystalline structures of the alloys are calculated. The results have shown that the formed bcc phase is a compound based B2 structure where there is partial ionic bonding between A1 and other transition metals and hence the bcc structure of the alloys should be a B2 instead of an A2.

The catalytic mechanism of Fe-type nitrile hydratases (NHase) is studied by examining the pH and temperature dependence of the kinetic parameters along with the solvent isotope effect for the Fe-type NHase from Comamonas testosteriome Ni1 ([C.sub.t]NHase). The similarities in the kinetic data obtained for both Co- and Fe-type NHase enzyme have shown that both types of NHase enzymes have hydrated nitriles in a similar fashion.

An approach is developed based on gas-membrane technology that has allowed the exploration of the deformation mechanism simultaneously at high temperature and ultrahigh pressure. The method could be applied to study texture changes in iron during deformation and phase transformation in three phases in situ, namely, bcc (alpha), fcc (gamma), and hcp (epsi).

The effect of temperature on the interaction between a screw dislocation and a nanosized bcc Cu precipitate in bcc Fe is studied by using molecular dynamics simulations. The results have shown temperature dependence in the antitwinning direction, whereby the screw dislocation has bypassed the Cu precipitate by Orowan looping below 200 K, but has sheared the precipitate above 300 K.

A combination of Rutherford backscattering/channeling spectrometry and time-of-flight elastic recoil detection analysis is used to study the undoped wurtzite GaN epilayers implanted at room temperature with 50-325 keV [Fe.sup.+] ions. The results showed that both radiation enhanced diffusion and the thermal diffusion of Fe atoms near the surface should be at least five times larger than ordinary bulk diffusion in order to explain the increased Fe surface concentration.

The mixing situation of Fe and Co atoms implanting onto Cu(001) substrate is examined with regard to substrate temperature and deposition rate by using molecular dynamics. The results have shown that the morphology of the layer is under epitaxial growth as the substrate temperature is 700 or 1000K, while it is not epitaxial at the substrate temperature of 300 or 450 K.

The grazing incidence x-ray reflectivity technique is employed to study the electron density profiles and other characteristics of the ruthenium (Ru) nano-oxide layer present in the CoFe-Ru-CoFe trilayer system. The Ru layer is shown to confirm the thermal stability of the spacer layer after annealing.

The effects of substitution of Cu and Fe for Cd in Cd[Cr.sub.2][S.sub.4] on magnetic properties and magnetic entropy changes are examined. The maximum values of magnetic entropy change have suggested a potential of the sulfospinel as a magnetic refrigerant in the corresponding temperature range.

The magnetic properties observed after thermomagnetic treatment for a large field induced anisotropy Co-Fe-Nb-Si-B based alloy are compared with two Co-Fe-Zr-B-Cu based alloys. The transverse field annealed Co-rich amorphous Co-Fe-Zr-B alloys have displayed properties that are competitive with the field crystallized Co-rich Co-Fe-Nb-Si-B alloys.