Science.gov

Sample records for al fe mg

  1. Chemical ordering and large tunnel magnetoresistance in Co2FeAl/MgAl2O4/Co2FeAl(001) junctions

    NASA Astrophysics Data System (ADS)

    Scheike, Thomas; Sukegawa, Hiroaki; Inomata, Koichiro; Ohkubo, Tadakatsu; Hono, Kazuhiro; Mitani, Seiji

    2016-05-01

    Epitaxial magnetic tunnel junctions (MTJs) with a Co2FeAl/CoFe (0.5 nm)/MgAl2O4/Co2FeAl(001) structure were fabricated by magnetron sputtering. High-temperature in situ annealing led to a high degree of B2-order in the Co2FeAl layers and cation order of the MgAl2O4 barrier. Large tunnel magnetoresistance (TMR) of up to 342% was obtained at room temperature (616% at 4 K), in contrast to the TMR ratio ( ≲ 160%) suppressed by the band-folding effect in Fe/cation-ordered MgAl2O4/Fe MTJs. The present study reveals that the high degree of B2-order and the resulting high spin polarization in the Co2FeAl electrodes enable us to bypass the band-folding problem in spinel barriers.

  2. Evolution of Fe Bearing Intermetallics During DC Casting and Homogenization of an Al-Mg-Si Al Alloy

    NASA Astrophysics Data System (ADS)

    Kumar, S.; Grant, P. S.; O'Reilly, K. A. Q.

    2016-06-01

    The evolution of iron (Fe) bearing intermetallics (Fe-IMCs) during direct chill casting and homogenization of a grain-refined 6063 aluminum-magnesium-silicon (Al-Mg-Si) alloy has been studied. The as-cast and homogenized microstructure contained Fe-IMCs at the grain boundaries and within Al grains. The primary α-Al grain size, α-Al dendritic arm spacing, IMC particle size, and IMC three-dimensional (3D) inter-connectivity increased from the edge to the center of the as-cast billet; both α c-AlFeSi and β-AlFeSi Fe-IMCs were identified, and overall α c-AlFeSi was predominant. For the first time in industrial billets, the different Fe-rich IMCs have been characterized into types based on their 3D chemistry and morphology. Additionally, the role of β-AlFeSi in nucleating Mg2Si particles has been identified. After homogenization, α c-AlFeSi predominated across the entire billet cross section, with marked changes in the 3D morphology and strong reductions in inter-connectivity, both supporting a recovery in alloy ductility.

  3. Spin-orbit torque in Cr/CoFeAl/MgO and Ru/CoFeAl/MgO epitaxial magnetic heterostructures

    NASA Astrophysics Data System (ADS)

    Wen, Zhenchao; Kim, Junyeon; Sukegawa, Hiroaki; Hayashi, Masamitsu; Mitani, Seiji

    2016-05-01

    We study the spin-orbit torque (SOT) effective fields in Cr/CoFeAl/MgO and Ru/CoFeAl/MgO magnetic heterostructures using the adiabatic harmonic Hall measurement. High-quality perpendicular-magnetic-anisotropy CoFeAl layers were grown on Cr and Ru layers. The magnitudes of the SOT effective fields were found to significantly depend on the underlayer material (Cr or Ru) as well as their thicknesses. The damping-like longitudinal effective field (ΔHL) increases with increasing underlayer thickness for all heterostructures. In contrast, the field-like transverse effective field (ΔHT) increases with increasing Ru thickness while it is almost constant or slightly decreases with increasing Cr thickness. The sign of ΔHL observed in the Cr-underlayer devices is opposite from that in the Ru-underlayer devices while ΔHT shows the same sign with a small magnitude. The opposite directions of ΔHL indicate that the signs of spin Hall angle in Cr and Ru are opposite, which are in good agreement with theoretical predictions. These results show sizable contribution from SOT even for elements with small spin orbit coupling such as 3d Cr and 4d Ru.

  4. Evaluation of thermochemical data on Fe-Mg olivine, orthopyroxene, spinel and Ca-Fe-Mg-Al garnet

    SciTech Connect

    Chatterjee, N.

    1987-09-01

    Thermochemical data on Fe-Mg olivine, orthopyroxene, spinel and Ca-Fe-Mg garnet have been tested and reevaluated in reproducing experimental equilibrium data. All data (except of spinel) adjusted in this process lie within the error limits of original calorimetric experiments. For spinel, an enthalpy of -2307.2 kJmol and an entropy of 81.5 Jmol-K has been recommended. Recommended interaction parameters for the spinel-hercynite and forsterite-fayalite solutions are as follows: Spinel: W/sub (spinel-hercynite)/= 9124.0 Jmol. W/sub (hercynite-spinel)/ = 0.0 Jmol. Olivine: W = 4500.0 Jmol for 1 cation. Excess entropies (on 1 cation basis) necessary to reproduce phase equilibria for the pyrope-almandine and almandine-grossular solutions are as follows: Mg-Fe garnet: Wsub(pyrope-almandine) = 11.760 - 0.0016T Jmol-K. Wsub(almandine-pyrope) = -10.146 + 0.0037T Jmol-K. Fe-Ca garnet: W/sup s/ = -16.07 + 0.0126T Jmol-K.

  5. Hot Tear Susceptibility of Al-Mg-Si-Fe Alloys with Varying Iron Contents

    NASA Astrophysics Data System (ADS)

    Sweet, Lisa; Easton, Mark A.; Taylor, John A.; Grandfield, John F.; Davidson, Cameron J.; Lu, Liming; Couper, Malcolm J.; StJohn, David H.

    2013-12-01

    Hot tear susceptibility in cast Al-0.52Si-0.34Mg- xFe 6060 aluminum alloys was investigated using a hot tearing test apparatus to simulate hot tearing in DC casting. The test apparatus has two cast bars, one that is used to measure the load response and one which is fixed at both ends to restrain thermal contraction so that hot tearing can be observed and rated where it occurred. The iron (Fe) content, ranging from 0.02 to 0.5 wt pct, was seen to have a major influence on the load response during solidification and the tear rating of these alloys. The findings are discussed in terms of Rappaz-Drezet-Gremaud (RDG) model sensitivity analysis and related to the effect of Fe content on the morphology and prevalence of the β-Al5FeSi and α-AlFeSi intermetallic phases and their influence on the coherency and coalescence of the microstructure.

  6. Elastic moduli of nanocrystalline binary Al alloys with Fe, Co, Ti, Mg and Pb alloying elements

    NASA Astrophysics Data System (ADS)

    Babicheva, Rita I.; Bachurin, Dmitry V.; Dmitriev, Sergey V.; Zhang, Ying; Kok, Shaw Wei; Bai, Lichun; Zhou, Kun

    2016-05-01

    The paper studies the elastic moduli of nanocrystalline (NC) Al and NC binary Al-X alloys (X is Fe, Co, Ti, Mg or Pb) by using molecular dynamics simulations. X atoms in the alloys are either segregated to grain boundaries (GBs) or distributed randomly as in disordered solid solution. At 0 K, the rigidity of the alloys increases with decrease in atomic radii of the alloying elements. An addition of Fe, Co or Ti to the NC Al leads to increase in the Young's E and shear μ moduli, while an alloying with Pb decreases them. The elastic moduli of the alloys depend on a distribution of the alloying elements. The alloys with the random distribution of Fe or Ti demonstrate larger E and μ than those for the corresponding alloys with GB segregations, while the rigidity of the Al-Co alloy is higher for the case of the GB segregations. The moduli E and μ for polycrystalline aggregates of Al and Al-X alloys with randomly distributed X atoms are estimated based on the elastic constants of corresponding single-crystals according to the Voigt-Reuss-Hill approximation, which neglects the contribution of GBs to the rigidity. The results show that GBs in NC materials noticeably reduce their rigidity. Furthermore, the temperature dependence of μ for the NC Al-X alloys is analyzed. Only the Al-Co alloy with GB segregations shows the decrease in μ to the lowest extent in the temperature range of 0-600 K in comparison with the NC pure Al.

  7. Numerical Study of Microstructural Evolution During Homogenization of Al-Si-Mg-Fe-Mn Alloys

    NASA Astrophysics Data System (ADS)

    Priya, Pikee; Johnson, David R.; Krane, Matthew J. M.

    2016-09-01

    Microstructural evolution during homogenization of Al-Si-Mg-Fe-Mn alloys occurs in two stages at different length scales: while holding at the homogenization temperature (diffusion on the scale of the secondary dendrite arm spacing (SDAS) in micrometers) and during quenching to room temperature (dispersoid precipitation at the nanometer to submicron scale). Here a numerical study estimates microstructural changes during both stages. A diffusion-based model developed to simulate evolution at the SDAS length scale predicts homogenization times and microstructures matching experiments. That model is coupled with a Kampmann Wagner Neumann-based precipitate nucleation and growth model to study the effect of temperature, composition, as-cast microstructure, and cooling rates during posthomogenization quenching on microstructural evolution. A homogenization schedule of 853 K (580 °C) for 8 hours, followed by cooling at 250 K/h, is suggested to optimize microstructures for easier extrusion, consisting of minimal α-Al(FeMn)Si, no β-AlFeSi, and Mg2Si dispersoids <1 μm size.

  8. Solubility and release of fenbufen intercalated in Mg, Al and Mg, Al, Fe layered double hydroxides (LDH): The effect of Eudragit S 100 covering

    SciTech Connect

    Arco, M. del; Fernandez, A.; Martin, C.; Rives, V.

    2010-12-15

    Following different preparation routes, fenbufen has been intercalated in the interlayer space of layered double hydroxides with Mg{sup 2+} and Al{sup 3+} or Mg{sup 2+}, Al{sup 3+} and Fe{sup 3+} in the layers. Well crystallized samples were obtained in most of the cases (intercalation was not observed by reconstruction of the MgAlFe matrix), with layer heights ranging between 16.1 and 18.8 A. The presence of the LDH increases the solubility of fenbufen, especially when used as a matrix. The dissolution rate of the drug decreases when the drug is intercalated, and is even lower in those systems containing iron; release takes place through ionic exchange with phosphate anions from the solution. Preparation of microspheres with Eudragit S 100 leads to solids with an homogeneous, smooth surface with efficient covering of the LDH surface, as drug release was not observed at pH lower than 7. - Graphical abstract: LDHs containing Mg, Al, Fe increase fenbufen solubility, release takes place through ionic exchange with phosphate anions from the medium. Spherical solids with homogeneous, smooth surface are formed when using Eudragit S 100, efficiently covering the LDH surface. Display Omitted

  9. Layered double hydroxides as adsorbents and carriers of the herbicide (4-chloro-2-methylphenoxy)acetic acid (MCPA): systems Mg-Al, Mg-Fe and Mg-Al-Fe.

    PubMed

    Bruna, F; Celis, R; Pavlovic, I; Barriga, C; Cornejo, J; Ulibarri, M A

    2009-09-15

    Hydrotalcite-like compounds [Mg(3)Al(OH)(8)]Cl x 4H(2)O; [Mg(3)Fe(OH)(8)]Cl x 4H(2)O; [Mg(3)Al(0.5)Fe(0.5)(OH)(8)]Cl x 4H(2)O (LDHs) and calcined product of [Mg(3)Al(OH)(8)]Cl x 4H(2)O, Mg(3)AlO(4.5) (HT500), were studied as potential adsorbents of the herbicide MCPA [(4-chloro-2-methylphenoxy)acetic acid] as a function of pH, contact time and pesticide concentration, and also as support for the slow release of this pesticide, with the aim to reduce the hazardous effects that it can pose to the environment. The information obtained in the adsorption study was used for the preparation of LDH-MCPA complexes. The results showed high and rapid adsorption of MCPA on the adsorbents as well as that MCPA formulations based on LDHs and HT500 as pesticide supports displayed controlled release properties and reduced herbicide leaching in soil columns compared to a standard commercial MCPA formulation. Thereby, we conclude that the LDHs employed in this study can be used not only as adsorbents to remove MCPA from aqueous solutions, but also as supports for the slow release of this highly mobile herbicide, thus controlling its immediate availability and leaching. PMID:19380194

  10. Assessment of Post-eutectic Reactions in Multicomponent Al-Si Foundry Alloys Containing Cu, Mg, and Fe

    NASA Astrophysics Data System (ADS)

    Javidani, Mousa; Larouche, Daniel; Grant Chen, X.

    2015-07-01

    Post-eutectic reactions occurring in Al-Si hypoeutectic alloys containing different proportions of Cu, Mg, and Fe were thoroughly investigated in the current study. As-cast microstructures were initially studied by optical and electron microscopy to investigate the microconstituents of each alloy. Differential scanning calorimetry (DSC) was then used to examine the phase transformations occurring during the heating and cooling processes. Thermodynamic calculations were carried out to assess the phase formation under equilibrium and in nonequilibrium conditions. The Q-Al5Cu2Mg8Si6 phase was predicted to precipitate from the liquid phase, either at the same temperature or earlier than the θ-Al2Cu phase depending on the Cu content of the alloy. The AlCuFe-intermetallic, which was hardly observed in the as-cast microstructure, significantly increased after the solution heat treatment in the alloys containing high Cu and Fe contents following a solid-state transformation of the β-Al5FeSi phase. After the solution heat treatment, the AlCuFe-intermetallics were mostly identified with the stoichiometry of the Al7Cu2Fe phase. Thermodynamic calculations and microstructure analysis helped in determining the DSC peak corresponding to the melting temperature of the N-Al7Cu2Fe phase. The effect of Cu content on the formation temperature of π-Al8Mg3FeSi6 is also discussed.

  11. Perpendicular Magnetic Anisotropy of Full-Heusler Films in Pt/Co2FeAl/MgO Trilayers

    NASA Astrophysics Data System (ADS)

    Li, Xiaoqi; Yin, Shaoqian; Liu, Yupeng; Zhang, Delin; Xu, Xiaoguang; Miao, Jun; Jiang, Yong

    2011-04-01

    We report on perpendicular magnetic anisotropy (PMA) in a Pt/Co2FeAl/MgO sandwiched structure with a thick Co2FeAl layer of 2-2.5 nm. The PMA is thermally stable and the anisotropy energy density Ku is 1.3×106 erg/cm3 for the structure with 2 nm Co2FeAl after annealing at 350 °C. The annealing temperature and Co2FeAl thickness greatly affect the PMA. Our results provide an effective way to realize relatively thick perpendicularly magnetized Heusler alloy films.

  12. Perpendicular magnetic anisotropy in Ta/Co2FeAl/MgO multilayers

    NASA Astrophysics Data System (ADS)

    Gabor, M. S.; Petrisor, T.; Tiusan, C.; Petrisor, T.

    2013-08-01

    In this paper, we demonstrate the stabilization of perpendicular magnetic anisotropy (PMA) in Ta/Co2FeAl/MgO multilayers sputtered on thermally oxidized Si(100) substrates. The magnetic analysis points out that these films show significant interfacial anisotropy even in the as-deposited state, KS=0.67 erg/cm2, enough to provide PMA for the as-deposited films with thicknesses below 1.5 nm. Moreover, the interfacial anisotropy is enhanced by thermal annealing up to 300 °C. The presence of a magnetic dead layer, whose thickness increases with annealing temperature, was also identified.

  13. Structural defects analysis versus spin polarized tunneling in Co2FeAl/MgO/CoFe magnetic tunnel junctions with thick MgO barriers

    NASA Astrophysics Data System (ADS)

    Gabor, M. S.; Tiusan, C.; Petrisor, T.; Petrisor, T.; Hehn, M.; Lu, Y.; Snoeck, E.

    2013-12-01

    We report on spin polarization reduction by incoherent tunneling in single crystal Co2FeAl/MgO/Co50Fe50 magnetic tunnel junctions (MTJs). A large density of misfit dislocations in the Heusler based MTJs has been provided by a thick MgO barrier and its 3.8% lattice mismatch with the Co2FeAl electrode. Our analysis implicates a correlated structural-transport approach. The crystallographic coherence in the real space has been investigated by High Resolution Transmission Electron Microscopy phase analysis. The electronic transport experiments in variable temperature, fitted with a theoretical extended-Glazman-Matveev model, address different levels of the tunneling mechanisms from direct to multi-center hopping. We demonstrate a double impact of dislocations, as extended defects, on the tunneling polarization. Firstly, the breaking of the crystal symmetry destroys the longitudinal and lateral coherence of the propagating Bloch functions. This affects the symmetry filtering efficiency of the Δ1 states across the (001) MgO barriers and reduces the associated effective tunneling polarization. Secondly, dislocations provide localized states within the MgO gap. This determines temperature activated spin-conserving inelastic tunneling through chains of defects which are responsible for the one order of magnitude drop of the tunnel magnetoresistance from low to room temperature.

  14. High-pressure behaviour of Cr-Fe-Mg-Al spinels: applications to diamond geobarometry

    NASA Astrophysics Data System (ADS)

    Periotto, Benedetta; Bruschini, Enrico; Nestola, Fabrizio; Lenaz, Davide; Princivalle, Francesco; Andreozzi, Giovanni B.; Bosi, Ferdinando

    2014-05-01

    Spinels belonging to the chromite - magnesiochromite - hercynite (FeCr2O4-MgCr2O4-FeAl2O4) system are among the most common inclusions found in diamonds (Stachel and Harris 2008). In particular, although FeCr2O4 and MgCr2O4 components sum to between 85 and 88% of spinels found in diamonds, hercynite FeAl2O4 plays a not negligible role in determining their thermo-elastic properties with concentrations reaching 7-9 % (other minor end-members like MgAl2O4, MgFe2O4 and Fe2O3 rarely reach 2-3% in total, see Lenaz et al. 2009). Recent studies were focused on the determination of the diamond formation pressure by the so-called "elastic method" (see for example Nestola et al. 2011 and references therein). It was demonstrated that accurate and precise thermo-elastic parameters are fundamental to minimize the uncertainty of formation pressure. In this work we have determined the equations of state at room temperature of three synthetic spinel end-members chromite - magnesiochromite - hercynite and one natural spinel crystal extracted from a diamond (from Udachnaya mine, Siberia, Russia) by single-crystal X-ray diffraction in situ at high-pressure. A diamond-anvil cell was mounted on a STADI IV diffractometer equipped with a point detector and motorized by SINGLE software (Angel and Finger 2011). The natural crystal was investigated to test (and possibly validate) the "empirical prediction model", capable to provide bulk modulus and its first pressure derivative only knowing the composition of the spinels found in diamonds. Such prediction model could be used to obtain pressure of formation for the diamond-spinel pair through the elastic method. Details and results will be discussed. The research was funded by the ERC Starting Grant to FN (grant agreement n° 307322). References Angel R.J., Finger L.W. (2011) SINGLE A program to control single-crystal diffractometers. Journal of Applied Crystallography, 44, 247-251. Lenaz D., Logvinova A.M., Princivalle F., Sobolev N. (2009

  15. Effect of inorganic and organic ligands on the sorption/desorption of arsenate on/from Al-Mg and Fe-Mg layered double hydroxides.

    PubMed

    Caporale, A G; Pigna, M; Dynes, J J; Cozzolino, V; Zhu, J; Violante, A

    2011-12-30

    This paper describes the sorption of arsenate on Al-Mg and Fe-Mg layered double hydroxides as affected by pH and varying concentrations of inorganic and organic ligands, and the effect of residence time on the desorption of arsenate by ligands. The capacity of ligands to inhibit the fixation of arsenate followed the sequence: nitrateAl-Mg-LDH and nitrateFe-Mg-LDH. The inhibition of arsenate sorption increased by increasing the initial ligand concentration and was greater on Al-Mg-LDH than on Fe-Mg-LDH. The longer the arsenate residence time on the LDH surfaces the less effective the competing ligands were in desorbing arsenate from sorbents. A greater percentage of arsenate was removed by phosphate from Al-Mg-LDH than from Fe-Mg-LDH, due to the higher affinity of arsenate for iron than aluminum. PMID:22071258

  16. Effect of inorganic and organic ligands on the sorption/desorption of arsenate on/from Al-Mg and Fe-Mg layered double hydroxides

    NASA Astrophysics Data System (ADS)

    Caporale, A. G.; Pigna, M.; Dynes, J. J.; Cozzolino, V.; Zhu, J.; Violante, A.

    2012-04-01

    In recent decades, a class of anionic clays known as layered double hydroxides (LDHs) has attracted substantial attention due to the potential use in many applications, such as photochemistry, electrochemistry, polymerization, magnetization and biomedical science. There has also been considerable interest in using LDHs as adsorbents to remove environmental contaminants due to their large surface area, high anion exchange capacity and good thermal stability. We studied the sorption of arsenate on Al-Mg and Fe-Mg layered double hydroxides (easily reproducible at low-cost) as affected by pH and varying concentrations of inorganic (nitrate, nitrite, phosphate, selenite and sulphate) and organic (oxalate and tartrate) ligands, ii) the effect of residence time on the arsenate desorption by these ligands, and iii) the kinetics of arsenate desorption by phosphate. The Fe-Mg-LDH sorbed nearly twice the amount of arsenate compared to the Al-Mg-LDH, due, in part, to its greater surface area and lower degree of crystallinity. Moreover, the Fe-Mg-LDH sorbed more arsenate than phosphate, in contrast to the Al-Mg-LDH, which adsorbed more phosphate than arsenate, probably because of the greater affinity of arsenate than phosphate for Fe sites and, vice versa, the greater affinity of phosphate than arsenate for Al sites. Arsenate sorption onto samples decreased by increasing pH, due, maybe, to the high affinity of hydroxyl ions for LDHs and/or to the value of zero point charge of two sorbents. The rate of decline in the amount of arsenate sorbed was, however, relatively constant, decreasing the fastest for the Fe-Mg-LDH compared to the Al-Mg-LDH. The capacity of ligands to inhibit the fixation of arsenate followed the sequence: nitrate < nitrite < sulphate < selenite < tartrate < oxalate << phosphate on Al-Mg-LDH and nitrate < sulphate ≈ nitrite < tartrate < oxalate < selenite << phosphate on Fe-Mg-LDH. The inhibition of arsenate sorption increased by increasing the initial

  17. Major soil element (Ca, Mg, K, Na, Al, Fe) distribution along the Qinghai-Tibet Railway

    NASA Astrophysics Data System (ADS)

    Wang, Z.; Zhang, Y.; Zhang, H.; Ding, M.; Lin, X.

    2011-12-01

    The Tibetan Plateau (TP), which has been called the third polar region, is the highest plateau in the world. There are a series of special soils present in the TP, which are extremely important in soil sciences for their particularities. Soil chemical composition is one of the necessary indices of soil characteristics. The major element content of the soil, such as Ca, Mg, K, Na, not only can affect the soil pH value and soil fertility but also are the main drivers of soil geochemical processes. It is helpful to understand the TP environmental characteristics, to study the major soil element content.The Qinghai-Tibet Railway (QTR) is the highest-elevation and the longest highland railway on earth. There are nearly all types of TP soil along the QTR. Most of the areas along the QTR are in fairly pristine condition. This offers a good platform to study the natural environmental characteristics of the soil. This study selected 240 soil samples from 28 sample areas along the Qinghai-Tibet Railway, and the aluminum, iron, calcium, sodium, potassium and magnesium content in the soil were measured with ICP-AES. The results indicated: (1) Compared with the national soil background values, the Ca content in soil was higher along the QTR and Al was lower; but the Fe, Mg, K and Na contents were similar. (2) Along the whole QTR, the soil Al, Fe and Mg content showed a decreasing trend from Xining to Lhasa, the changes in K and Na values were relatively complex, and the distribution of Ca could be divided three sections. (3) The soil element contents varied with different soil types and parent materials. Most of the six elements content was minimum in soil, which derived from debris materials for ice and water, and the elements content was maximum in soil, which evolved from debris for flood, and the content of soil Ca developed from debris for lake was maximum. The amount of each element present in the Hapli-Cryic Aridosols and Calci-Cryic Aridosols was relatively higher than

  18. Lattice-matched magnetic tunnel junctions using a Heusler alloy Co2FeAl and a cation-disorder spinel Mg-Al-O barrier

    NASA Astrophysics Data System (ADS)

    Scheike, Thomas; Sukegawa, Hiroaki; Furubayashi, Takao; Wen, Zhenchao; Inomata, Koichiro; Ohkubo, Tadakatsu; Hono, Kazuhiro; Mitani, Seiji

    2014-12-01

    Perfectly lattice-matched magnetic tunnel junctions (MTJs) consisting of a Heusler alloy B2-Co2FeAl (CFA) electrode and a cation-disorder spinel (Mg-Al-O) barrier were fabricated by sputtering and plasma oxidation. We achieved a large tunnel magnetoresistance (TMR) ratio of 228% at room temperature (RT) (398% at 5 K) for the epitaxial CFA/MgAl-O/CoFe(001) MTJ, in which the effect of lattice defects on TMR ratios is excluded. With inserting a ultrathin (≤1.5 nm) CoFe layer between the CFA and Mg-Al-O, the TMR ratio further increased up to 280% at RT (453% at 5 K), which reflected the importance of controlling barrier-electrode interface states other than the lattice matching.

  19. Evolution of Intermetallics, Dispersoids, and Elevated Temperature Properties at Various Fe Contents in Al-Mn-Mg 3004 Alloys

    NASA Astrophysics Data System (ADS)

    Liu, K.; Chen, X.-G.

    2015-12-01

    Nowadays, great interests are rising on aluminum alloys for the applications at elevated temperature, driven by the automotive and aerospace industries requiring high strength, light weight, and low-cost engineering materials. As one of the most promising candidates, Al-Mn-Mg 3004 alloys have been found to possess considerably high mechanical properties and creep resistance at elevated temperature resulted from the precipitation of a large number of thermally stable dispersoids during heat treatment. In present work, the effect of Fe contents on the evolution of microstructure as well as high-temperature properties of 3004 alloys has been investigated. Results show that the dominant intermetallic changes from α-Al(MnFe)Si at 0.1 wt pct Fe to Al6(MnFe) at both 0.3 and 0.6 wt pct Fe. In the Fe range of 0.1-0.6 wt pct studied, a significant improvement on mechanical properties at elevated temperature has been observed due to the precipitation of dispersoids, and the best combination of yield strength and creep resistance at 573 K (300 °C) is obtained in the 0.3 wt pct Fe alloy with the finest size and highest volume fraction of dispersoids. The superior properties obtained at 573 K (300 °C) make 3004 alloys more promising for high-temperature applications. The relationship between the Fe content and the dispersoid precipitation as well as the materials properties has been discussed.

  20. SDAS, Si and Cu Content, and the Size of Intermetallics in Al-Si-Cu-Mg-Fe Alloys

    NASA Astrophysics Data System (ADS)

    Sivarupan, Tharmalingam; Taylor, John Andrew; Cáceres, Carlos Horacio

    2015-05-01

    Plates of Al-(a)Si-(b)Cu-Mg-(c)Fe alloys with varying content of (mass pct) Si ( a = 3, 4.5, 7.5, 9, 10, or 11), Cu ( b = 0, 1, or 4), and Fe ( c = 0.2, 0.5 or 0.8) were cast in sand molds with a heavy chill at one end to ensure quasi-directional solidification over a wide range of Secondary Dendrite Arm Spacing (SDAS). Statistical analysis on the size of the β-Al5FeSi, α-Al8Fe2Si, or Al2Cu intermetallics on Backscattered Electron images showed that a high Si content reduced the size of the β platelets in alloys with up to 0.5 Fe content regardless of the SDAS, whereas at small SDAS the refining effect extended up to 0.8 Fe, and involved α-phase intermetallics which replaced the beta platelets at those concentrations. At low Si contents, a high Cu level appeared to have similar refining effects as increased Si, through the formation of α-phase particles in the post-eutectic stage which agglomerated with the Al2Cu intermetallics. A high content of Si appears to make the overall refining process less critical in terms of SDAS/cooling rate.

  1. A clear oscillation of the interlayer exchange coupling in Co2FeAl/Cr/Co2FeAl structure with MgO capping layer

    NASA Astrophysics Data System (ADS)

    Xu, Xiaoguang; Zhang, Jianli; Sha, Lei; Zhang, Delin; Jiang, Yong

    2012-10-01

    We have studied the interlayer exchange coupling in Co2FeAl (CFA)/Cr/CFA/MgO multilayers via both experiments and numerical simulation. Magnetization measurement on the films shows a clear oscillation attenuation behavior with the thickness (0.6 nm < t < 10 nm) of the Cr spacer layer, and the oscillation period is about 2.1 nm. The numerical simulation demonstrates that the interlayer exchange coupling between CFA layers is 90° coupling having an oscillation behavior, which is in good agreement with the experiments. MgO capping layer is supposed to be a key factor for the clear periodic oscillation behavior in CFA/Cr/CFA trilayers.

  2. The Effects of Individual Metal Contents on Isochrones for C, N, O, Na, Mg, Al, Si, and Fe

    NASA Astrophysics Data System (ADS)

    Beom, Minje; Na, Chongsam; Ferguson, Jason W.; Kim, Y.-C.

    2016-08-01

    The individual characteristics of C, N, O, Na, Mg, Al, Si, and Fe on isochrones have been investigated in this study. Stellar models have been constructed for various mixtures in which the content of each element is changed up to the extreme value reported in recent studies, and the changes in isochrone shape have been analyzed for the various mixtures. To express the abundance variation of different elements with a single parameter, we have focused on the relative changes in the total number of metal ions. A review of the shape changes revealed that Na, Mg, and Al work the same way in stellar models, similar to the well-known fact that C, N, and O have the same reactions in the stellar interior. In addition, it was found that in high-metallicity conditions the influence of Si and Fe on the red giant branch becomes smaller than that of Na, Mg, and Al closer to the tip. Furthermore, the influence of Fe on the main sequence is larger than that of Na, Mg, Al, and even Si.

  3. Influence cobalt on microstructural and hardness property of Al-Zn-Mg-Cu-Fe-Cr-Ni P/ M alloys

    NASA Astrophysics Data System (ADS)

    Naeem, Haider T.; Mohammad, Kahtan S.; Hussin, Kamarudin; Rahmat, Azim; Bashirom, Nurhuda

    2015-05-01

    In this study, influence cobalt additives on the microstructural and hardness properties of an Al-Zn-Mg-Cu-Fe-Cr-Ni PM alloy undergone the retrogression and re-aging treatment were carried out. Green compacts pressed at 370 MPa were then sintered at temperature 650°C in argon atmosphere for two hours. The sintered compacts subjected to a homogenizing treated at 470°C for 1.5 hours then aged at 120°C for 24 hours and retrogressed at 180°C for 30 minutes, and then re-aged at 120°C for 24 hours. Microstructural results of the Al-Zn-Mg-Cu-Fe-Cr-Ni-Co alloys introduced an intermetallics compound in the matrix of alloy, identified as the Al5Co2, Al70Co20Ni10 and Al4Ni3 phases besides to the MgZn2 and Mg2Zn11 phases which produced of the precipitation hardening during heat treatment. These compounds with precipitates provided strengthening of dispersion that led to improved Vickers's hardness and dinsifications properties of the alloy. The highest Vickers hardness of aluminum alloy containing cobalt was gotten after applying the retrogression and re-aging treatment.

  4. Tunnel magnetoresistance in textured Co2FeAl/MgO/CoFe magnetic tunnel junctions on a Si/SiO2 amorphous substrate

    NASA Astrophysics Data System (ADS)

    Wen, Zhenchao; Sukegawa, Hiroaki; Mitani, Seiji; Inomata, Koichiro

    2011-05-01

    Magnetic tunnel junctions with B2-ordered Co2FeAl full Heusler alloy as a ferromagnetic electrode were fabricated by sputtering on thermally oxidized Si/SiO2 amorphous substrates. A Co2FeAl/MgO/Co50Fe50 structure showed a highly (001)-textured structure and the tunneling magnetoresistance (TMR) ratio of 166% at room temperature and 252% at 48 K were achieved. The temperature dependence of TMR can be fitted with spin wave excitation model, and the bias voltage dependence of differential conductance demonstrated that the high TMR was mainly contributed by coherent tunneling. This work suggests the B2-Co2FeAl is one of the promising candidates for practical spintronic applications.

  5. Perpendicular magnetization of Co2FeAl full-Heusler alloy films induced by MgO interface

    NASA Astrophysics Data System (ADS)

    Wen, Zhenchao; Sukegawa, Hiroaki; Mitani, Seiji; Inomata, Koichiro

    2011-06-01

    The perpendicular magnetization of Co2FeAl (CFA) full-Heusler alloy films was achieved in the structures of CFA/MgO and MgO/CFA with the perpendicular magnetic anisotropy energy density (KU) of 2-3×106 erg/cm3, which can be used as the perpendicular ferromagnetic electrodes of MgO-based magnetic tunnel junctions (MTJs) with high thermal stability at sub-50-nm dimension. The CFA thickness dependence of KU was investigated at different annealing temperatures, indicating that the perpendicular anisotropy of CFA is contributed by the interfacial anisotropy between CFA and MgO. This letter will open up a way for obtaining perpendicular magnetization of Co-based full-Heusler alloys, which is promising for further reduction in the critical current of current induced magnetization switching in MgO-based MTJ nanopillars with perpendicular full-Heusler alloy electrodes.

  6. Equilibrium and kinetics studies on As(V) and Sb(V) removal by Fe2+ -doped Mg-Al layered double hydroxides.

    PubMed

    Kameda, Tomohito; Kondo, Eisuke; Yoshioka, Toshiaki

    2015-03-15

    Mg-Al layered double hydroxides (Mg-Al LDHs) doped with Fe(2+) adsorbed As(V) [Formula: see text] and Sb(V) [Formula: see text] from an aqueous solution through anion exchange with Cl(-) intercalated in the LDH interlayer. Fe(2+)-doped Mg-Al LDH exhibited superior As(V) removal compared with Mg-Al LDH. The oxidation of Fe(2+) doped in the Mg-Al LDH host layer to Fe(3+) increased the positive layer charge of the LDH, thus increasing the anion-uptake capacity owing to stronger electrostatic attractive force between the positively charged layer and the anion. However, Fe(2+)-doped Mg-Al LDH was not superior to Mg-Al LDH in terms of Sb(V) removal. This was attributed to the preferential intercalation of OH(-) over [Formula: see text] . The As(V) and Sb(V) removal by LDH followed Langmuir-type adsorption, which proceeded via a pseudo-first-order reaction. The equilibrium and kinetics studies confirm that the adsorption of As(V) and Sb(V) by Fe(2+)-doped Mg-Al LDH was the result of chemical adsorption, involving the anion exchange of [Formula: see text] and [Formula: see text] with the intercalated Cl(-).

  7. Co2FeAl based magnetic tunnel junctions with BaO and MgO/BaO barriers

    NASA Astrophysics Data System (ADS)

    Rogge, J.; Hetaba, W.; Schmalhorst, J.; Bouchikhaoui, H.; Stender, P.; Baither, D.; Schmitz, G.; Hütten, A.

    2015-07-01

    We succeed to integrate BaO as a tunneling barrier into Co2FeAl based magnetic tunnel junctions (MTJs). By means of Auger electron spectroscopy it could be proven that the applied annealing temperatures during BaO deposition and afterwards do not cause any diffusion of Ba neither into the lower Heusler compound lead nor into the upper Fe counter electrode. Nevertheless, a negative tunnel magnetoresistance (TMR) ratio of -10% is found for Co2FeAl (24 nm) / BaO (5 nm) / Fe (7 nm) MTJs, which can be attributed to the preparation procedure and can be explained by the formation of Co- and Fe-oxides at the interfaces between the Heusler and the crystalline BaO barrier by comparing with theory. Although an amorphous structure of the BaO barrier seems to be confirmed by high-resolution transmission electron microscopy (TEM), it cannot entirely be ruled out that this is an artifact of TEM sample preparation due to the sensitivity of BaO to moisture. By replacing the BaO tunneling barrier with an MgO/BaO double layer barrier, the electric stability could effectively be increased by a factor of five. The resulting TMR effect is found to be about +20% at room temperature, although a fully antiparallel state has not been realized.

  8. Mg-Al and Zn-Fe layered double hydroxides used for organic species storage and controlled release.

    PubMed

    Seftel, E M; Cool, P; Lutic, D

    2013-12-01

    Layered double hydroxides (LDH) containing (Mg and Al) or (Zn and Fe) were prepared by coprecipitation at constant pH, using NaOH and urea as precipitation agents. The most pure LDH phase in the Zn/Fe system was obtained with urea and in Mg/Al system when using NaOH. The incorporation of phenyl-alanine (Phe) anions in the interlayer of the LDH was performed by direct coprecipitation, ionic exchange and structure reconstruction of the mixed oxide obtained by the calcination of the coprecipitated product at 400°C. The reconstruction method and the direct coprecipitation in a medium containing Phe in the initial mixture were less successful in terms of high yields of organic-mineral composite than the ionic exchange method. A spectacular change in sample morphology and yield in exchanged solid was noticed for the Zn3Fe sample obtained by ionic exchange for 6h with Phe solution. A delivery test in PBS of pH=7.4 showed the release of the Phe in several steps up to 25 h indicating different host-guest interactions between the Phe and the LDH matrix. This behavior makes the preparation useful to obtain late delivery drugs, by the incorporation of the anion inside the LDH layer.

  9. Giant tunneling magnetoresistance up to 330% at room temperature in sputter deposited Co{sub 2}FeAl/MgO/CoFe magnetic tunnel junctions

    SciTech Connect

    Wang Wenhong; Sukegawa, Hiroaki; Shan, Rong; Mitani, Seiji; Inomata, Koichiro

    2009-11-02

    Magnetoresistance ratio up to 330% at room temperature (700% at 10 K) has been obtained in a spin-valve-type magnetic tunnel junction (MTJ) consisting of a full-Heusler alloy Co{sub 2}FeAl electrode and a MgO tunnel barrier fabricated on a single crystal MgO (001) substrate by sputtering method. The output voltage of the MTJ at one-half of the zero-bias value was found to be as high as 425 mV, which is the largest reported to date in MTJs using Heusler alloy electrodes. The present finding suggests that Co{sub 2}FeAl may be one of the most promising candidates for future spintronics devices applications.

  10. The mechanical and electronic properties of Al/TiC interfaces alloyed by Mg, Zn, Cu, Fe and Ti: First-principles study

    NASA Astrophysics Data System (ADS)

    Sun, Ting; Wu, Xiaozhi; Li, Weiguo; Wang, Rui

    2015-03-01

    The adhesion and ductility of (100) and (110) Al/TiC interfaces alloyed by Mg, Zn, Cu, Fe, and Ti have been investigated using first-principles methods. Fe and Ti can enhance the adhesion of (100) and (110) interfaces. Mg and Zn have the opposite effect. Interfacial electronic structures have been created to analyze the changes of the work of adhesion. It is found that more charge is accumulated at interfaces alloyed by Fe and Ti compared with pure Al/TiC. There is also an obvious downward shift in the Fermi energy of Fe, Ti at the interface. Furthermore, the unstable stacking fault energies of the interfaces are calculated; the results demonstrate that the preferred slip direction is the < 110> direction for (100) and (110) Al/TiC. Based on the Rice criterion of ductility, the results predict that Mg, Fe, and Ti are promising candidates for improving the ductility of Al/TiC interfaces.

  11. Magnetic properties of a Pt/Co2FeAl/MgO structure with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Li, Xiao-Qi; Xu, Xiao-Guang; Wang, Sheng; Wu, Yong; Zhang, De-Lin; Miao, Jun; Jiang, Yong

    2012-10-01

    Microstructures and magnetic properties of Ta/Pt/Co2FeAl (CFA)/MgO multilayers are studied to understand perpendicular magnetic anisotropy (PMA) of half-metallic full-Heusler alloy films. PMA is realized in a 2.5-nm CFA film with B2-ordered structure observed by a high resolution transmission electron microscope. It is demonstrated that a high quality interface between the ferromagnetic layer and oxide layer is not essential for PMA. The conversions between in-plane anisotropy and PMA are investigated to study the dependence of magnetic moment on temperature. At the intersection points, the decreasing slope of the saturation magnetization (Ms) changes because of the conversions. The dependence of Ms on the annealing temperature and MgO thickness is also studied.

  12. Perpendicular magnetic anisotropy in Ta|Co{sub 40}Fe{sub 40}B{sub 20}|MgAl{sub 2}O{sub 4} structures and perpendicular CoFeB|MgAl{sub 2}O{sub 4}|CoFeB magnetic tunnel junction

    SciTech Connect

    Tao, B. S.; Li, D. L.; Yuan, Z. H.; Liu, H. F.; Ali, S. S.; Feng, J. F.; Wei, H. X.; Han, X. F.; Liu, Y.; Zhao, Y. G.; Zhang, Q.; Guo, Z. B.; Zhang, X. X.

    2014-09-08

    Magnetic properties of Co{sub 40}Fe{sub 40}B{sub 20} (CoFeB) thin films sandwiched between Ta and MgAl{sub 2}O{sub 4} layers have been systematically studied. For as-grown state, Ta/CoFeB/MgAl{sub 2}O{sub 4} structures exhibit good perpendicular magnetic anisotropy (PMA) with interface anisotropy K{sub i} = 1.22 erg/cm{sup 2}, which further increases to 1.30 erg/cm{sup 2} after annealing, while MgAl{sub 2}O{sub 4}/CoFeB/Ta multilayer shows in-plane magnetic anisotropy and must be annealed in order to achieve PMA. For bottom CoFeB layer, the thickness window for PMA is from 0.6 to 1.0 nm, while that for top CoFeB layer is between 0.8 and 1.4 nm. Perpendicular magnetic tunnel junctions (p-MTJs) with a core structure of CoFeB/MgAl{sub 2}O{sub 4}/CoFeB have also been fabricated and tunneling magnetoresistance ratio of about 36% at room temperature and 63% at low temperature have been obtained. The intrinsic excitations in the p-MTJs have been identified by inelastic electron-tunneling spectroscopy.

  13. Stability of the assemblage orthopyroxene-sillimanite-quartz in the system MgO-FeO-Fe2O3-Al2O3-SiO2-H2O

    NASA Astrophysics Data System (ADS)

    Annersten, H.; Seifert, F.

    1981-06-01

    The stability of coexisting orthopyroxene, sillimanite and quartz and the composition of orthopyroxene in this assemblage has been determined in the system MgO-FeO-Fe2O3-Al2O3-SiO2-H2O as a function of pressure, mainly at 1,000° C, and at oxygen fugacities defined mostly by the hematite-magnetite buffer. The upper stability of the assemblage is terminated at 17 kbars, 1,000° C, by the reaction opx+Al-silicate →gar+qz, proceeding toward lower pressures with increasing Fe/(Fe+Mg) ratio in the system. The lower stability is controlled by the reaction opx+sill+qz→ cord, which occurs at 11 kbars in the iron-free system but is lowered to 9 kbars with increasing Fe/(Fe+Mg). Spinel solid solutions are stabilized, besides quartz, up to 14 kbars in favour of garnet in the iron-rich part of the system (Fe/(Fe+Mg)≧0.30). Ferric-ferrous ratios in orthopyroxene are increasing with increasing ferro-magnesian ratio. At least part of the generally observed increase in Al content with Fe2+ in orthopyroxene is not due to an increased solubility of the MgAlAlSiO6 component but rather of a MgFe3+AlSiO6 component. The data permit an estimate of oxygen fugacity from the composition of orthopyroxene in coexistence with sillimanite and quartz.

  14. Spin-orbit torques and magnetization switching in W/Co2FeAl/MgO structures

    NASA Astrophysics Data System (ADS)

    Gabor, M. S.; Petrisor, T., Jr.; Mos, R. B.; Mesaros, A.; Nasui, M.; Belmeguenai, M.; Zighem, F.; Tiusan, C.

    2016-09-01

    Magnetization switching by current induced spin-orbit torques (SOTs) in heavy metal/ferromagnetic metal/oxide structures is of great research interest due to its potential applications in the field of low power consumption spintronic devices. Here, we study the Slonczewski-like and the field-like SOT effective fields in β-W/Co2FeAl/MgO structures showing perpendicular magnetic anisotropy (PMA). We characterize the SOT effective fields using harmonic Hall voltage measurements and we point out the essential role of the planar Hall effect corrections. We estimate that for bulk β-W an effective spin Hall angle as large as 0.3  ±  0.03 and a spin diffusion length of 2.2  ±  0.3 nm. Moreover, we demonstrate SOT-induced magnetization switching for charge current densities of the order of 106 A cm-2.

  15. Spin–orbit torques and magnetization switching in W/Co2FeAl/MgO structures

    NASA Astrophysics Data System (ADS)

    Gabor, M. S.; Petrisor, T., Jr.; Mos, R. B.; Mesaros, A.; Nasui, M.; Belmeguenai, M.; Zighem, F.; Tiusan, C.

    2016-09-01

    Magnetization switching by current induced spin–orbit torques (SOTs) in heavy metal/ferromagnetic metal/oxide structures is of great research interest due to its potential applications in the field of low power consumption spintronic devices. Here, we study the Slonczewski-like and the field-like SOT effective fields in β-W/Co2FeAl/MgO structures showing perpendicular magnetic anisotropy (PMA). We characterize the SOT effective fields using harmonic Hall voltage measurements and we point out the essential role of the planar Hall effect corrections. We estimate that for bulk β-W an effective spin Hall angle as large as 0.3  ±  0.03 and a spin diffusion length of 2.2  ±  0.3 nm. Moreover, we demonstrate SOT-induced magnetization switching for charge current densities of the order of 106 A cm‑2.

  16. High-pressure, temperature elasticity of Fe- and Al-bearing MgSiO3: Implications for the Earth's lower mantle

    NASA Astrophysics Data System (ADS)

    Zhang, Shuai; Cottaar, Sanne; Liu, Tao; Stackhouse, Stephen; Militzer, Burkhard

    2016-01-01

    Fe and Al are two of the most important rock-forming elements other than Mg, Si, and O. Their presence in the lower mantle's most abundant minerals, MgSiO3 bridgmanite, MgSiO3 post-perovskite and MgO periclase, alters their elastic properties. However, knowledge on the thermoelasticity of Fe- and Al-bearing MgSiO3 bridgmanite, and post-perovskite is scarce. In this study, we perform ab initio molecular dynamics to calculate the elastic and seismic properties of pure, Fe3+- and Fe2+-, and Al3+-bearing MgSiO3 perovskite and post-perovskite, over a wide range of pressures, temperatures, and Fe/Al compositions. Our results show that a mineral assemblage resembling pyrolite fits a 1D seismological model well, down to, at least, a few hundred kilometers above the core-mantle boundary, i.e. the top of the D″ region. In D″, a similar composition is still an excellent fit to the average velocities and fairly approximate to the density. We also implement polycrystal plasticity with a geodynamic model to predict resulting seismic anisotropy, and find post-perovskite with predominant (001) slip across all compositions agrees best with seismic observations in the D″.

  17. Co2FeAl Heusler thin films grown on Si and MgO substrates: Annealing temperature effect

    NASA Astrophysics Data System (ADS)

    Belmeguenai, M.; Tuzcuoglu, H.; Gabor, M. S.; Petrisor, T.; Tiusan, C.; Zighem, F.; Chérif, S. M.; Moch, P.

    2014-01-01

    10 nm and 50 nm Co2FeAl (CFA) thin films have been deposited on MgO(001) and Si(001) substrates by magnetron sputtering and annealed at different temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth (according to CFA(001)[110]//MgO(001)[100] epitaxial relation) for CFA films grown on a Si and on a MgO substrate, respectively. For these later, the chemical order varies from the A2 phase to the B2 phase when increasing the annealing temperature (Ta), while only the A2 disorder type has been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR) measurements revealed that the in-plane anisotropy results from the superposition of a uniaxial and a fourfold symmetry term for CFA grown on MgO substrates. This fourfold anisotropy, which disappears completely for samples grown on Si, is in accord with the crystal structure of the samples. The fourfold anisotropy field decreases when increasing Ta, while the uniaxial anisotropy field is nearly unaffected by Ta within the investigated range. The MS-FMR data also allow for concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with Ta. Finally, the FMR linewidth decreases when increasing Ta, due to the enhancement of the chemical order. We derive a very low intrinsic damping parameter (1.1×10-3 and 1.3×10-3 for films of 50 nm thickness annealed at 615 °C grown on MgO and on Si, respectively).

  18. The Molar Volume of FeO-MgO-Fe2O3-Cr2O3-Al2O3-TiO2 Spinels

    NASA Astrophysics Data System (ADS)

    Hamecher, E. A.; Antoshechkina, P. M.; Ghiorso, M. S.; Asimow, P. D.

    2011-12-01

    A new model of molar volume has been calibrated in the spinel supersystem (Mg,Fe2+)(Al,Cr,Fe3+)2O4 - (Mg,Fe2+)2TiO4. A total of 832 X-ray and neutron diffraction experiments performed on spinels at ambient and in situ high-P, T conditions (from the American Mineralogist Crystal Structure Database (Downs and Hall-Wallace, 2003) and other sources) were used to calibrate end-member equations of state and an excess volume model for this system. The effect on molar volume of cation ordering over the octahedral and tetrahedral sites is captured with linear dependence on Mg2+, Al3+, and Fe3+ site occupancy terms. We allowed standard state volumes and coefficients of thermal expansion of the end members to vary within their uncertainties during extraction of the mixing properties, in order to achieve the best fit. Published equations of states of the various spinel end members were analyzed to obtain optimal values of the bulk modulus and its pressure derivative, for each explicit end member. For any spinel composition in the supersystem, the model molar volume is obtained by adding excess volume and cation order-dependent terms to a linear combination of the five end member volumes, estimated at pressure and temperature using the high-T Vinet equation of state. The model has a total of 31 parameters and fits nearly all experiments to within 0.02 J/bar/mol, or better than 0.5% in volume. The model is compared to the current MELTS (Ghiorso and Sack, 1995; Ghiorso et al., 2002) spinel model with a demonstration of the impact of the model difference on the estimated spinel-garnet lherzolite transition pressure. Our primary motivation in this work is the development of a comprehensive spinel molar volume model for use in calibration of activity-composition models of garnet and pyroxene solid solutions. The thermodynamic models, along with a new silicate liquid equation of state, will be incorporated into the next generation MELTS model, xMELTS. The new solid solution models

  19. Thermal elasticity of Fe- and Al-bearing and -free MgSiO3-perovskite

    NASA Astrophysics Data System (ADS)

    Shukla, G.; Wu, Z.; Wentzcovitch, R. M.

    2013-12-01

    We present a thorough analysis of the thermal elastic properties of iron- and aluminum-bearing and -free MgSiO3-perovskite. Results from different first principles methods are compared to experimental data available and results for elastic moduli and velocities are analyzed at lower mantle conditions. Velocity heterogeneity produced by temperature variations and variation of aluminum and iron content are carefully examined and contrasted. This analysis is essential for improving understanding of the constitution of Earth's lower mantle. Research supported by NSF awards EAR-1319361, -1019853, and -0810272.

  20. Fabrication of MgAl{sub 2}O{sub 4} tunnel barrier by radio frequency-sputtering method and magnetoresistance effect through it with Fe or Fe{sub 4}N ferromagnetic electrode

    SciTech Connect

    Tsunoda, Masakiyo; Chiba, Ryoichi; Kabara, Kazuki

    2015-05-07

    Spinel MgAl{sub 2}O{sub 4} thin films were deposited on MgO single-crystal substrates and epitaxial Fe (or Fe{sub 4}N) thin films by RF-sputtering from a ceramic target. Epitaxial relationship was confirmed by X-ray diffraction analysis between the crystalline spinel MgAl{sub 2}O{sub 4} films and the respective substrate and underlayers, while no diffraction peak was observed from the films deposited on amorphous substrates. Spin-valve type magnetic tunnel junctions (MTJs) with a stacking structure of Fe [Fe{sub 4}N]/MgAl{sub 2}O{sub 4}/CoFeB/Ru/Fe/MnIr exhibited normal [inverse] tunnel magnetoresistance (TMR) effect, reflecting the sign of spin polarization of Fe [Fe{sub 4}N]. The maximum magnitude of the TMR ratio obtained for the Fe-based and Fe{sub 4}N-based MTJs was 67% and 18%, respectively. The resistance area product values of the MTJs were significantly larger than the reported values for the MTJs with a post-oxidized spinel MgAl{sub 2}O{sub 4} barrier.

  1. Fabrication of MgAl2O4 tunnel barrier by radio frequency-sputtering method and magnetoresistance effect through it with Fe or Fe4N ferromagnetic electrode

    NASA Astrophysics Data System (ADS)

    Tsunoda, Masakiyo; Chiba, Ryoichi; Kabara, Kazuki

    2015-05-01

    Spinel MgAl2O4 thin films were deposited on MgO single-crystal substrates and epitaxial Fe (or Fe4N) thin films by RF-sputtering from a ceramic target. Epitaxial relationship was confirmed by X-ray diffraction analysis between the crystalline spinel MgAl2O4 films and the respective substrate and underlayers, while no diffraction peak was observed from the films deposited on amorphous substrates. Spin-valve type magnetic tunnel junctions (MTJs) with a stacking structure of Fe [Fe4N]/MgAl2O4/CoFeB/Ru/Fe/MnIr exhibited normal [inverse] tunnel magnetoresistance (TMR) effect, reflecting the sign of spin polarization of Fe [Fe4N]. The maximum magnitude of the TMR ratio obtained for the Fe-based and Fe4N-based MTJs was 67% and 18%, respectively. The resistance area product values of the MTJs were significantly larger than the reported values for the MTJs with a post-oxidized spinel MgAl2O4 barrier.

  2. Thermal equation of state of CaFe 2O 4-type MgAl 2O 4

    NASA Astrophysics Data System (ADS)

    Sueda, Yuichiro; Irifune, Tetsuo; Sanehira, Takeshi; Yagi, Takehiko; Nishiyama, Norimasa; Kikegawa, Takumi; Funakoshi, Ken-ichi

    2009-05-01

    In situ X-ray diffraction measurements of CaFe 2O 4-type MgAl 2O 4 have been conducted at pressures up to 42 GPa and temperatures to 2400 K using Kawai-type multianvil apparatus with sintered diamond anvils. Additional measurements have also been conducted at pressures to 12 GPa using diamond anvil cell with helium as a pressure medium at room temperature, and at temperatures to 836 K at the ambient pressure using a high-temperature X-ray diffractometer. The analysis of room-temperature data yielded V0 = 240.1(2) Å 3, K0 = 205(6) GPa, and K0=4.1(3). A fit of the present data to high-temperature Birch-Murnaghan equation of state (EOS) yielded (∂ K0/∂ T) P = -0.030(2) GPa/K and α0 = a0 + b0T with values of a0 = 1.96(13) × 10 -5 K -1 and b0 = 1.64(24) × 10 -8 K -2. The present data set was also fitted to Mie-Grüneisen-Debye (MGD) EOS and we obtained γ0 = 1.73(7), q = 2.03(37), and θ0 = 1546(104) K. Density changes of MORB have been estimated using the newly obtained thermoelastic parameters, assuming that the Al-rich phase in this composition possesses the CaFe 2O 4-type structure under the lower mantle P, T conditions. The calculated densities along geotherms for the normal mantle and subducting cold slabs are both significantly higher than those of typical seismological models, confirming the conclusion of some recent results on MORB by laser-heated diamond anvil cell experiments.

  3. A vibrational spectroscopic study of the phosphate mineral lulzacite Sr2Fe2+(Fe2+,Mg)2Al4(PO4)4(OH)10

    NASA Astrophysics Data System (ADS)

    Frost, Ray L.; López, Andrés; Belotti, Fernanda M.; Xi, Yunfei; Scholz, Ricardo

    2014-06-01

    The mineral lulzacite from Saint-Aubin des Chateaux mine, France, with theoretical formula Sr2Fe2+(Fe2+,Mg)2Al4(PO4)4(OH)10 has been studied using a combination of electron microscopy with EDX and vibrational spectroscopic techniques. Chemical analysis shows a Sr, Fe, Al phosphate with minor amounts of Ga, Ba and Mg. Raman spectroscopy identifies an intense band at 990 cm-1 with an additional band at 1011 cm-1. These bands are attributed to the PO43-ν1 symmetric stretching mode. The ν3 antisymmetric stretching modes are observed by a large number of Raman bands. The Raman bands at 1034, 1051, 1058, 1069 and 1084 together with the Raman bands at 1098, 1116, 1133, 1155 and 1174 cm-1 are assigned to the ν3 antisymmetric stretching vibrations of PO43- and the HOPO32- units. The observation of these multiple Raman bands in the symmetric and antisymmetric stretching region gives credence to the concept that both phosphate and hydrogen phosphate units exist in the structure of lulzacite. The series of Raman bands at 567, 582, 601, 644, 661, 673 and 687 cm-1 are assigned to the PO43-ν2 bending modes. The series of Raman bands at 437, 468, 478, 491, 503 cm-1 are attributed to the PO43- and HOPO32-ν4 bending modes. No Raman bands of lulzacite which could be attributed to the hydroxyl stretching unit were observed. Infrared bands at 3511 and 3359 cm-1 are ascribed to the OH stretching vibration of the OH units. Very broad bands at 3022 and 3299 cm-1 are attributed to the OH stretching vibrations of water. Vibrational spectroscopy offers insights into the molecular structure of the phosphate mineral lulzacite.

  4. XRD line-broadening characteristics of M-oxides (M = Mg, Mg-Al, Y, Fe) nanoparticles produced by coprecipitation method

    NASA Astrophysics Data System (ADS)

    Pratapa, S.; Susanti, L.; Insany, Y. A. S.; Alfiati, Z.; Hartono, B.; Mashuri, Taufiq, Ahmad; Fuad, Abdullah; Triwikantoro, Baqiya, M. A.; Purwaningsih, S.; Yahya, E.; Darminto

    2010-10-01

    Simple coprecipitation method has been used to produce nanoparticles of MgO (magnesia), MgOṡAl2O3 (spinel), Y2O3 (yttria) and Fe3O4 (ferrite). The raw materials were, in respective, magnesium powder, magnesium and aluminium powders, ytrria powder, and natural sand. The coprecipitation included the use of suitable acid and base to dissolve the powders or sand and to produce precipitates, as well as the use of water to wash and purify the precipitates, and drying at relatively low temperatures, namely lower than 100° C, followed by heating at 450° C, 750° C, 600° C and 200° C to produce magnesia, spinel, yttria and ferrite nanopowders, respectively. X-ray diffractometry was used to characterise the purity and nanocrystallinity of the final powders. It was found qualitatively that the powders were of high purity. Further line-broadening analysis using single-line and Rietveld-based softwares was performed to reveal the nanocrystallinity of the powders. Different line breadth values were found for the powders, indicating different crystallite sizes. It was also found that, particularly for spinel and yttria, the diffraction peaks exhibited `longer' tails, indicating broader crystallite size distribution. The average crystallite size for the powders ranged from 3 to 70 nm. The results could then be used as `fingerprints' for nanocrystallinity using x-ray diffractometry. The XRD crystallite sizes for yttria and ferrite nanocrystals are in fair agreement with their counterparts from electron microscopy observation.

  5. Adsorption of Cd(II) by Mg-Al-CO3- and magnetic Fe3O4/Mg-Al-CO3-layered double hydroxides: Kinetic, isothermal, thermodynamic and mechanistic studies.

    PubMed

    Shan, Ran-ran; Yan, Liang-guo; Yang, Kun; Hao, Yuan-feng; Du, Bin

    2015-12-15

    Understanding the adsorption mechanisms of metal cations on the surfaces of solids is important for determining the fate of these metals in water and wastewater treatment. The adsorption kinetic, isothermal, thermodynamic and mechanistic properties of cadmium (Cd(II)) in an aqueous solution containing Mg-Al-CO3- and magnetic Fe3O4/Mg-Al-CO3-layered double hydroxide (LDH) were studied. The results demonstrated that the adsorption kinetic and isotherm data followed the pseudo-second-order model and the Langmuir equation, respectively. The adsorption process of Cd(II) was feasible, spontaneous and endothermic in nature. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to explain the adsorption mechanisms. The characteristic XRD peaks and FTIR bands of CdCO3 emerged in the LDH spectra after Cd(II) adsorption, which indicated that the adsorption of Cd(II) by LDHs occurred mainly via CdCO3 precipitation, surface adsorption and surface complexation. Furthermore, the magnetic Fe3O4/Mg-Al-CO3-LDH can be quickly and easily separated using a magnet before and after the adsorption process.

  6. Co2FeAl thin films grown on MgO substrates: Correlation between static, dynamic, and structural properties

    NASA Astrophysics Data System (ADS)

    Belmeguenai, M.; Tuzcuoglu, H.; Gabor, M. S.; Petrisor, T., Jr.; Tiusan, C.; Berling, D.; Zighem, F.; Chauveau, T.; Chérif, S. M.; Moch, P.

    2013-05-01

    Co2FeAl (CFA) thin films with thickness varying from 10 to 115 nm have been deposited on MgO(001) substrates by magnetron sputtering and then capped by a Ta or Cr layer. X-ray diffraction (XRD) revealed that the cubic [001] CFA axis is normal to the substrate and that all the CFA films exhibit full epitaxial growth. The chemical order varies from the B2 phase to the A2 phase when decreasing the thickness. Magneto-optical Kerr effect (MOKE) and vibrating sample magnetometer (VSM) measurements show that, depending on the field orientation, one- or two-step switchings occur. Moreover, the films present a quadratic MOKE signal increasing with the CFA thickness, due to the increasing chemical order. Ferromagnetic resonance (FMR), MOKE transverse bias initial inverse susceptibility and torque (TBIIST) measurements reveal that the in-plane anisotropy results from the superposition of a uniaxial and of a fourfold symmetry term. The fourfold anisotropy is in accord with the crystal structure of the samples and is correlated to the biaxial strain and to the chemical order present in the films. In addition, a large negative perpendicular uniaxial anisotropy is observed. Frequency and angular dependencies of the ferromagnetic resonance linewidth show two magnon scattering and mosaicity contributions, which depend on the CFA thickness. A Gilbert damping coefficient as low as 0.0011 is found.

  7. Microstructure, Mechanical Properties, and Age-Hardening Behavior of an Al-Si-Fe-Mn-Cu-Mg Alloy Produced by Spray Deposition

    NASA Astrophysics Data System (ADS)

    Feng, Wang; Jishan, Zhang; Baiqing, Xiong; Yongan, Zhang

    2011-02-01

    It has been recognized generally that the spray-deposited process is an innovative technique of rapid solidification. In this paper, Al-20Si-5Fe-3Mn-3Cu-1Mg alloy was synthesized by the spray atomization and deposition technique. The microstructure and mechanical properties of the spray-deposited alloy were studied using x-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), and tensile tests. It is observed that the microstructure of spray-deposited Al-20Si-5Fe-3Mn-3Cu-1Mg alloy is composed of the α-Al,Si and the particle-like Al15(FeMn)3Si2 compounds. The aging process of the alloy was investigated by microhardness measurement, differential scanning calorimetry analysis, and TEM observations. The results indicate that the two types of precipitates, S-Al2CuMg and σ-Al5Cu6Mg2 precipitate from matrix and improve the tensile strength of the alloy efficiently at both the ambient and elevated temperatures (300 °C).

  8. Comparison of laser-induced and intrinsic tunnel magneto-Seebeck effect in CoFeB /MgAl2O4 and CoFeB/MgO magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Huebner, Torsten; Boehnke, Alexander; Martens, Ulrike; Thomas, Andy; Schmalhorst, Jan-Michael; Reiss, Günter; Münzenberg, Markus; Kuschel, Timo

    2016-06-01

    We present a comparison of the tunnel magneto-Seebeck effect for laser-induced and intrinsic heating. Therefore, Co40Fe40B20 /MgAl2O4 and Co25Fe55B20 /MgO magnetic tunnel junctions have been prepared. The TMS ratio of 3% in case of the MAO MTJ agrees well with ratios found for other barrier materials, while the TMS ratio of 23% of the MgO MTJ emphasizes the influence of the CoFe composition. We find results using the intrinsic method that differ in sign and magnitude in comparison to the results of the laser heating. The intrinsic contributions can alternatively be explained by the Brinkman model and the given junction properties. Especially, we are able to demonstrate that the symmetric contribution is solely influenced by the barrier asymmetry. Thus, we conclude that the symmetry analysis used for the intrinsic method is not suitable to unambiguously identify an intrinsic tunnel magneto-Seebeck effect.

  9. XRD line-broadening characteristics of M-oxides (M = Mg, Mg-Al, Y, Fe) nanoparticles produced by coprecipitation method

    SciTech Connect

    Pratapa, S.; Susanti, L.; Insany, Y. A. S.; Alfiati, Z.; Hartono, B.; Mashuri,; Triwikantoro; Baqiya, M. A.; Purwaningsih, S.; Yahya, E.; Darminto; Taufiq, Ahmad; Fuad, Abdullah

    2010-10-24

    Simple coprecipitation method has been used to produce nanoparticles of MgO (magnesia), MgO{center_dot}Al{sub 2}O{sub 3}(spinel), Y{sub 2}O{sub 3}(yttria) and Fe{sub 3}O{sub 4}(ferrite). The raw materials were, in respective, magnesium powder, magnesium and aluminium powders, ytrria powder, and natural sand. The coprecipitation included the use of suitable acid and base to dissolve the powders or sand and to produce precipitates, as well as the use of water to wash and purify the precipitates, and drying at relatively low temperatures, namely lower than 100 deg. C, followed by heating at 450 deg. C, 750 deg. C, 600 deg. C and 200 deg. C to produce magnesia, spinel, yttria and ferrite nanopowders, respectively. X-ray diffractometry was used to characterise the purity and nanocrystallinity of the final powders. It was found qualitatively that the powders were of high purity. Further line-broadening analysis using single-line and Rietveld-based softwares was performed to reveal the nanocrystallinity of the powders. Different line breadth values were found for the powders, indicating different crystallite sizes. It was also found that, particularly for spinel and yttria, the diffraction peaks exhibited 'longer' tails, indicating broader crystallite size distribution. The average crystallite size for the powders ranged from 3 to 70 nm. The results could then be used as 'fingerprints' for nanocrystallinity using x-ray diffractometry. The XRD crystallite sizes for yttria and ferrite nanocrystals are in fair agreement with their counterparts from electron microscopy observation.

  10. Role of Mg interlayers in Fe/Mg/MgO/Fe and Fe/Mg/MgO/Mg/Fe magnetic tunnel junctions

    SciTech Connect

    Wang, Y.; Zhang, J.; Zhang, Xiaoguang; Cheng, Hai-Ping; Han, Prof. X. F.

    2010-01-01

    -Fe(001)/Mg/MgO/Fe- and -Fe(001)/Mg/MgO/Mg/Fe- magnetic tunnel junctions (MTJs) with Mg interlayers are studied by first-principles calculation. An important role of the Mg interlayer is identified to be preserving the preferential transmission of the majority-spin states with \\Delta_1 symmetry, which dominate the spin-dependent electron transport of MTJs with MgO barrier. One layer of Mg at the electrode/barrier interface does not decrease the tunneling magnetoresistance (TMR) ratio nearly as much as one layer of oxide. At certain Mg thickness case the TMR could be strongly influenced by the resonance tunneling states in minority-spin channel, these states are mainly raised from the quantum-well states formed in the Mg interlayer and coupled with interfacial resonance states which are very sensitive to the interface structures.

  11. MgSiO3-FeSiO3-Al2O3 in the Earth's lower mantle: Perovskite and garnet at 1200 km depth

    NASA Technical Reports Server (NTRS)

    O'Neill, Bridget; Jeanloz, Raymond

    1994-01-01

    Natural pyroxene and garnet starting material are used to study the effects of joint Fe and Al substitution into MgSiO3 perovskite at approxmiately 50 GPa. Garnet is found to coexist with perovskite in samples containing both Fe and Al to pressures occurring deep into the lower mantel (approximately 1200 km depth). The volume of the perovskite unit cell is V(sub o(Angstrom(exp 3)) = 162.59 + 5.95x(sub FeSiO3) + 10.80x(sub Al2O3) with aluminum causing a significant increase in the distortion from the ideal cubic cell. On the basis of a proposed extension of the MgSiO3-Al2O3 high-pressure phase diagram toward FeSiO3, Fe is shown to partition preferentially into the garnet phase. The stability of garnet deep into the lower mantel may hinder the penetration of subducted slabs below the transition zone.

  12. Magnetic anisotropy and order structure of L10-FePt(001) single-crystal films grown epitaxially on (001) planes of MgO, SrTiO3, and MgAl2O4 substrates

    NASA Astrophysics Data System (ADS)

    Hotta, A.; Ono, T.; Hatayama, M.; Tsumura, K.; Kikuchi, N.; Okamoto, S.; Kitakami, O.; Shimatsu, T.

    2014-05-01

    L10-FePt(001) single-crystal films were grown epitaxially on SrTiO3(001), MgAl2O4(001), and MgO(001) substrates. Their uniaxial magnetic anisotropy Ku and the order structure were examined for the film thickness t range of 2-14 nm. All series of films show large Ku of 4 × 107 erg/cm3 in the thickness range higher than 10 nm, with order parameter S of 0.8 and saturation magnetization Ms of 1120 emu/cm3. Ku decreased gradually as t decreased. The Ku reduction was considerable when t decreased from 4 nm to 2 nm. No marked difference in the thickness dependence of Ku was found in any series of films, although the lattice mismatch between FePt and the substrates was markedly different. Ku reduction showed good agreement with the reduction of S for the films on MgAl2O4 and MgO. The Ku ˜ S2 plot showed an almost linear relation, which is in good agreement with theoretical predictions. Transmission electron microscopy images for a FePt film on MgO substrate revealed that the lattice mismatch between FePt(001) and MgO(001) was relaxed in the initial 1 or 2 layers of FePt(001) lattices, which is likely to be true also for two other series of films.

  13. High-pressure, temperature elasticity of Fe- and Al-bearing MgSiO3: implications for the Earth's lower mantle

    NASA Astrophysics Data System (ADS)

    Zhang, S.; Cottaar, S.; Liu, T.; Stackhouse, S.; Militzer, B.

    2015-12-01

    A good knowledge on the thermoelasticity of the major constitutional minerals, Fe- and Al-bearing MgSiO3 bridgmanite and post-perovskite (pPv), is one of the keys for understanding the lower mantle. However, the available data are scarce. By means of first-principles molecular dynamics simulations that treat all anharmonic effects accurately, we extensively explore the effects of the existence of Fe, including both Fe2+ and Fe3+, and Al on the elastic properties of MgSiO3, at different compositions and atomic distributions, mineral phases, and pressure and temperature conditions that are relevant to the Earth's lower mantle. Based on these results, we find that the laterally averaged (1D) density and seismic velocities support a pyrolitic composition across the whole lower mantle; we also study the transverse anisotropy of these minerals in a subducting slab near the core-mantle boundary, and confirm that the pPv phase with predominant (001) slip plane matches the seismic anisotropy in the D'' region independent of the amount of Fe or Al. These results provide a useful resource to investigate the seismic properties of mineral assemblages in the deep mantle and to explore the mineralogical origin of heterogeneities in the lower mantle.

  14. Effect of an interface Mg insertion layer on the reliability of a magnetic tunnel junction based on a Co2FeAl full-Heusler alloy

    NASA Astrophysics Data System (ADS)

    Lee, Jung-Min; Kil, Gyu Hyun; Lee, Gae Hun; Choi, Chul Min; Song, Yun-Heub; Sukegawa, Hiroaki; Mitani, Seiji

    2014-04-01

    The reliability of a magnetic tunnel junction (MTJ) based on a Co2FeAl (CFA) full-Heusler alloy with a MgO tunnel barrier was evaluated. In particular, the effect of a Mg insertion layer under the MgO was investigated in view of resistance drift by using various voltage stress tests. We compared the resistance change during constant voltage stress (CVS) and confirmed a trap/detrap phenomenon during the interval stress test for samples with and without a Mg insertion layer. The MTJ with a Mg insertion layer showed a relatively small resistance change for the CVS test and a reduced trap/detrap phenomenon for the interval stress test compared to the sample without a Mg insertion layer. This is understood to be caused by the improved crystallinity at the bottom of the CFA/MgO interface due to the Mg insertion layer, which provides a smaller number of trap site during the stress test. As a result, the interface condition of the MgO layer is very important for the reliability of a MTJ using a full-Heusler alloy, and the the insert of a Mg layer at the MgO interface is expected to be an effective method for enhancing the reliability of a MTJ.

  15. Magnetization behavior of L10-ordered FePt alloy thin films prepared on MgO(100), MgAl2O4(100), and KTaO3(100) single-crystal substrates

    NASA Astrophysics Data System (ADS)

    Iwama, Hiroki; Doi, Masaaki; Shima, Toshiyuki

    2016-07-01

    In order to investigate the effects of lattice mismatch between FePt thin films and single-crystal substrates on the tetragonality and magnetization process, FePt thin films were fabricated on several single-crystal substrates such as KTaO3 (KTO) (100), MgAl2O4 (MAO) (100), and MgO(100) at a substrate temperature of 700 °C. The Fe content of the FePt films was varied from 45.0 to 50.8 at. %. In addition to the fundamental (002) peak, the (001) and (003) superlattice peaks were clearly observed in the X-ray diffraction patterns of all the samples, indicating the formation of the L10-ordered structure. The magnetization measurements show that all the samples were perpendicularly magnetized. Coercivities (H c) of 57.8, 52.5, and 3.3 kOe were obtained for the films with Fe49.3Pt50.7 (at. %) deposited on the MgO, MAO, and KTO substrates. The marked reduction in H c is considered to arise from the morphology of FePt thin films.

  16. Ferroindialite (Fe2+,Mg)2Al4Si5O18, a new beryl-group mineral from the Eifel volcanic region, Germany

    NASA Astrophysics Data System (ADS)

    Chukanov, N. V.; Aksenov, S. M.; Pekov, I. V.; Ternes, B.; Schüller, W.; Belakovskiy, D. I.; Van, K. V.; Blass, G.

    2014-12-01

    A new mineral, ferroindialite, a Fe2+-dominant analog of indialite, has been found in a pyrometamorphosed xenolith of pelitic rock hosted in alkaline basalts. Associated minerals are phlogopite, sanidine, sillimanite, pyroxenes of the enstatite-ferrosilite series, wagnerite, fluorapatite, tridymite, zircon and almandine. Ferroindialite forms brown-purple to gray with a violet-blue tint short prismatic or thick tabular hexagonal crystals up to 1.5 mm in size. The new mineral is brittle, with a Mohs' hardness of 7. Cleavage is not observed. D meas = 2.66(1), D calc = 2.667 g/cm3. IR spectrum shows neither H2O nor OH groups. Ferroindialite is anomalously biaxial (-), α = 1.539(2), β = 1.552(2), γ = 1.554(2), 2 V meas = 30(10)°. The mineral is weakly pleochroic, ranging from colorless on X to pale violet on Z. Dispersion is weak, r < v. The chemical composition (electron microprobe, mean of five point analyses, wt %) is as follows: 0.14 Na2O, 0.46 K2O, 4.95 MgO, 1.13 MnO, 12.66 FeO, 2.64 Fe2O3, 30.45 Al2O3, 47.22 SiO2, total is 99.65. The distribution of total iron content between Fe2+ and Fe3+ was carried out according to structural data. The empirical formula of ferroindialite is: (K0.06Na0.03)(Fe{1.12/2+}Mg0.78Mn0.10)Σ2.00(Al3.79Fe{0.21/3+})Σ4.00Si4.98O18. The simplified formula is: (Fe2+,Mg)2Al4Si5O18. The crystal structure has been refined on a single crystal, R = 0.049. Ferroindialite is hexagonal, space group P6/ mcc; a = 9.8759(3), c = 9.3102(3) Å, V = 786.40(3) Å3, Z = 2. The strongest lines in the X-ray powder diffraction pattern [ d, Å ( I, %) ( hkl)] are: 8.59 (100) (100), 4.094 (27) (102), 3.390 (35) (112), 3.147 (19) (202), 3.055 (31) (211), 2.657 (12) (212), 1.695 (9) (224). The type specimen of ferroindialite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, registration number 4400/1.

  17. Co{sub 2}FeAl based magnetic tunnel junctions with BaO and MgO/BaO barriers

    SciTech Connect

    Rogge, J.; Schmalhorst, J.; Hütten, A.; Hetaba, W.

    2015-07-15

    We succeed to integrate BaO as a tunneling barrier into Co{sub 2}FeAl based magnetic tunnel junctions (MTJs). By means of Auger electron spectroscopy it could be proven that the applied annealing temperatures during BaO deposition and afterwards do not cause any diffusion of Ba neither into the lower Heusler compound lead nor into the upper Fe counter electrode. Nevertheless, a negative tunnel magnetoresistance (TMR) ratio of -10% is found for Co{sub 2}FeAl (24 nm) / BaO (5 nm) / Fe (7 nm) MTJs, which can be attributed to the preparation procedure and can be explained by the formation of Co- and Fe-oxides at the interfaces between the Heusler and the crystalline BaO barrier by comparing with theory. Although an amorphous structure of the BaO barrier seems to be confirmed by high-resolution transmission electron microscopy (TEM), it cannot entirely be ruled out that this is an artifact of TEM sample preparation due to the sensitivity of BaO to moisture. By replacing the BaO tunneling barrier with an MgO/BaO double layer barrier, the electric stability could effectively be increased by a factor of five. The resulting TMR effect is found to be about +20% at room temperature, although a fully antiparallel state has not been realized.

  18. Analysis of the Fe-Ce-O-C- M phase diagrams ( M = Ca, Mg, Al, Si) by constructing a component-solubility surface

    NASA Astrophysics Data System (ADS)

    Mikhailov, G. G.; Makrovets, L. A.; Smirnov, L. A.; Dresvyankina, L. E.

    2016-06-01

    Analysis of the ternary phase diagrams of Ce2O3- and CeO2-containing oxide systems allowed us to find the oxide compounds that form during steel deoxidizing with cerium and with cerium together with aluminum, calcium, magnesium, or silicon. The temperature dependences of the equilibrium constants of formation of Ce2O3 oxides and Ce2O3 · Al2O3, Ce2O3 · 11Al2O3, Ce2O3 · 2SiO2, 7Ce2O3 · 9SiO2 and Ce2O3 · SiO2 compounds are found. Surfaces for the component solubility in metallic melts Fe-Al-Ce-O-C, Fe- Ca-Ce-O-C, Fe-Mg-Ce-O-C, and Fe-Si-Ce-O-C are constructed. Nonmetallic inclusions that form in the course of experimental melts of St20 steel after its deoxidizing with silicocalcium and rare-earth metal (REM)-containing master alloys in a ladle furnace after degassing are studied. Phase inhomogeneity of the inclusions is found. As a rule, they consist of phases classified into the following three groups: oxide-sulfide, sulfide-oxide, and multiphase oxide-sulfide melt. Calcium aluminates are found to be components of complex sulfide-oxide noncorrosive inclusions.

  19. Temperature dependence of the perpendicular magnetic anisotropy in Ta/Co2FeAl/MgO structures probed by Anomalous Hall Effect

    NASA Astrophysics Data System (ADS)

    Gabor, M. S.; Petrisor, T.; Pop, O.; Colis, S.; Tiusan, C.

    2015-10-01

    We report a detailed study of the temperature dependence of the magnetic anisotropy in Ta/Co2FeAl/MgO structures by means of Anomalous Hall Effect measurements. The volume magnetic anisotropy, although negligible at room temperature, shows a non-negligible value at low temperatures and favors an in-plane easy magnetization axis. The surface magnetic anisotropy, which promotes the perpendicular magnetic easy axis, shows an increase from 0.76 ± 0.05 erg /cm2 at 300 K, up to 1.08 ± 0.04 erg /cm2 at 5 K, attributed to the evolution of the Co2FeAl layer saturation magnetization with temperature.

  20. Tululite, Ca14(Fe3+,Al)(Al,Zn,Fe3+,Si,P,Mn,Mg)15O36: a new Ca zincate-aluminate from combustion metamorphic marbles, central Jordan

    NASA Astrophysics Data System (ADS)

    Khoury, Hani N.; Sokol, Ella V.; Kokh, Svetlana N.; Seryotkin, Yurii V.; Nigmatulina, Elena N.; Goryainov, Sergei V.; Belogub, Elena V.; Clark, Ian D.

    2016-02-01

    Tululite (Ca14(Fe3+,Al)(Al,Zn,Fe3+,Si,P,Mn,Mg)15O36 (the hypothetical end-member formula Ca14{Fe3+O6}[SiO4][Zn5Al9]O26) (IMA2014-065) is a new natural Ca zincate-aluminate, identified in medium-temperature (800-850 °C) combustion metamorphic (CM) spurrite-fluorellestadite marbles from central Jordan. The type locality (Tulul Al Hammam area) is situated in the northern part of the Siwaqa complex, the largest area of the "Mottled Zone" Formation in the Dead Sea region. The marbles originated from bitumen-rich chalky marine sediments of the Maastrichtian-Paleogene Muwaqqar Chalk Marl Formation, which have low clay content (and, consequently, low Al) and high Zn, Cd, and U enrichments. The bulk CM rocks derived from the low-Al protolith have unusually high (Zn + Cd)/Al ratios ( 0.2) and, as a result, a mineralogy with negligibly small percentages of Ca aluminates having low Ca:Al molar ratios (minerals of mayenite supergroup, Ca:Al = 6:7) common to most of calcareous CM rocks in the Mottled Zone. Instead, the mineral assemblage of the Zn-rich marbles contains tululite, with high Ca:Al = 2.55 molar ratios and Zn substituting for a large portion of Al (Zn:Al = 1.1). Tululite occurs in thin clusters as irregular grains with indented outlines (20-100 μm in size), having typical open-work textures associated with rock-forming calcite, fluorellestadite, spurrite, and accessory Zn-rich periclase, lime-monteponite solid solutions, calcium uranates, and zincite. Marbles also bear brownmillerite, dorrite, fluormayenite, high-fluorine Ca aluminate, and lakargiite. Secondary phases are brucite, gel-like calcium silicate hydrates and calcium silicate aluminate hydrates, including Zn- and U-bearing and Cd-rich compounds, Si-bearing hydrated compounds after calcium uranates, and basic Cd chlorides. The empirical formula of the holotype tululite (a mean of 32 analyses) is (Ca13.29Cd0.75)Σ14.04(Al5.46Zn5.20Fe3+ 2.23Si0.95Mn3+ 1.01Mg0.78P0.41)Σ16.04O36. Tululite is cubic, space

  1. Melts in the Deep Earth: Calculating the Densities of CaO-FeO-MgO-Al2O3-SiO2 Liquids

    NASA Astrophysics Data System (ADS)

    Thomas, C.; Guo, X.; Agee, C. B.; Asimow, P. D.; Lange, R. A.

    2012-12-01

    We present new equation of state (EOS) measurements for hedenbergite (Hd, CaFeSi2O6) and forsterite (Fo, Mg2SiO4) liquids. These liquid EOS add to the basis set in the CaO-FeO-MgO-Al2O3-SiO2 (CMASF) oxide space at elevated temperatures and pressures; other liquids include: enstatite (En, MgSiO3), anorthite (An, CaAl2Si2O8), diopside (Di, CaMgSi2O6), and fayalite (Fa, Fe2SiO4). The Hd EOS measurement was a multi-technique collaboration using 1-atm double-bob Archimedean, ultrasonic, sink/float, and shock wave techniques. Un-weighted linear fitting of the shock data in shock velocity (US)-particle velocity (up) space defines a pre-heated (1400 °C) Hugoniot US = 2.628(0.024) + 1.54(0.01)up km/s. The slope corresponds to a K' of 5.16(0.04), consistent with piston-cylinder and multi-anvil sink/float experiments. The intercept is fixed at the ultrasonic sound speed (Co) since the unconstrained intercept is within the stated error. This behavior demonstrates consistency across methods and that the liquid is relaxed during shock compression. Shock compression of pre-heated (2000°C) single crystal Fo gives an un-weighted linear Hugoniot of US = 2.674(0.188) + 1.64(0.06)up km/s. The unconstrained Co falls below estimates based on extrapolation in both temperature and composition from two published partial molar sound speed models, 3.195m/s [1] and 3.126 m/s [2]. The shock-derived Co indicates that dC/dT is negative for Fo liquid, contrary to the positive [1] and zero [2] temperature dependences derived over relatively narrow temperature intervals. CMASF liquid isentropes were calculated using five end-members (En, Fo, Fa, An, Di). For modeling crystallization of a fictive magma ocean, we examined two liquids: peridotite [3] (P=.33En+.56Fo+.07Fa+.03An+.007Di) and simplified chondrite [4] (Ch=.62En+.24Fo+.08Fa+.04An+.02Di). Each end-member is defined by a 3rd or 4th order Birch-Murnaghan isentrope, Mie-Grüneisen thermal pressure and a constant heat capacity. The volumes are

  2. Vibrational spectroscopic characterization of the phosphate mineral kulanite Ba(Fe2+,Mn2+,Mg)2(Al,Fe3+)2(PO4)3(OH)3

    NASA Astrophysics Data System (ADS)

    Frost, Ray L.; López, Andrés; Xi, Yunfei; Granja, Amanda; Scholz, Ricardo

    2013-11-01

    The mineral kulanite BaFe2Al2(PO4)3(OH)3, a barium iron aluminum phosphate, has been studied by using a combination of electron microscopy and vibrational spectroscopy. Scanning electron microscopy with EDX shows the mineral is homogenous with no other phases present. The Raman spectrum is dominated by an intense band at 1022 cm-1 assigned to the PO43-ν1 symmetric stretching mode. Low intensity Raman bands at 1076, 1110, 1146, 1182 cm-1 are attributed to the PO43-ν3 antisymmetric stretching vibrations. The infrared spectrum shows a complex spectral profile with overlapping bands. Multiple phosphate bending vibrations supports the concept of a reduction in symmetry of the phosphate anion. Raman spectrum at 3211, 3513 and 3533 cm-1 are assigned to the stretching vibrations of the OH units. Vibrational spectroscopy enables aspects on the molecular structure of kulanite to be assessed.

  3. A vibrational spectroscopic study of the phosphate mineral zanazziite - Ca2(MgFe2+)(MgFe2+Al)4Be4(PO4)6ṡ6(H2O)

    NASA Astrophysics Data System (ADS)

    Frost, Ray L.; Xi, Yunfei; Scholz, Ricardo; Belotti, Fernanda M.; Dias Menezes Filho, Luiz Alberto

    2013-03-01

    Zanazziite is the magnesium member of a complex beryllium calcium phosphate mineral group named roscherite. The studied samples were collected from the Ponte do Piauí mine, located in Itinga, Minas Gerais. The mineral was studied by electron microprobe, Raman and infrared spectroscopy. The chemical formula can be expressed as Ca2.00(Mg3.15,Fe0.78,Mn0.16,Zn0.01,Al0.26,Ca0.14)Be4.00(PO4)6.09(OH)4.00ṡ5.69(H2O) and shows an intermediate member of the zanazziite-greinfeinstenite series, with predominance of zanazziite member. The molecular structure of the mineral zanazziite has been determined using a combination of Raman and infrared spectroscopy. A very intense Raman band at 970 cm-1 is assigned to the phosphate symmetric stretching mode whilst the Raman bands at 1007, 1047, 1064 and 1096 cm-1 are attributed to the phosphate antisymmetric stretching mode. The infrared spectrum is broad and the antisymmetric stretching bands are prominent. Raman bands at 559, 568, 589 cm-1 are assigned to the ν4 out of plane bending modes of the PO4 and HPO4 units. The observation of multiple bands supports the concept that the symmetry of the phosphate unit in the zanazziite structure is reduced in symmetry. Raman bands at 3437 and 3447 cm-1 are attributed to the OH stretching vibrations; Raman bands at 3098 and 3256 are attributed to water stretching vibrations. The width and complexity of the infrared spectral profile in contrast to the well resolved Raman spectra, proves that the pegmatitic phosphates are better studied with Raman spectroscopy.

  4. The Perovskite to Post-Perovskite phase transition in Al-bearing (Mg,Fe)SiO3: A XANES in-situ analysis at the Fe K-edge

    NASA Astrophysics Data System (ADS)

    Andrault, D.; Munoz, M.; Bolfan-Casanova, N.; Guignot, N.; Perrillat, J.; Aquilanti, G.; Pascarelli, S.

    2008-12-01

    Phase transition from perovskite (Pv) to Post-Pv (PPv) phase in MgSiO3 has been studied by many groups since its discovery in 2004 (1,2) and the different studies find similar transition pressures. The effect of Al and Fe on the phase transition remains more controversial. The most recent studies suggest an increase of the transition pressure with increasing Fe-content (3,4), but other experimental work (5) as well as ab-initio calculations (6) show the opposite effect. The effect of Al was reported to increase slightly the pressure transition to the CaIrO3 form (4,7), but its influence on the Fe3+ content in the PPv phase has not been documented yet. By means of in situ study of the Fe K-edge fine structures (XANES), we investigated the phase relations between Pv and PPv phases for three different Al-(Mg,Fe)SiO3 compositions. For this, we synthesized various Pv and PPv mixtures using laser-heated diamond anvil cell (DAC) for pressures between 60 and 170 GPa. The sample's mineralogy, i.e. the Pv and PPv phase fractions, was determined using in-situ X-ray diffraction at the ID27 beamline of the ESRF (8,9). Then, we probed the Fe speciation, i.e. the Fe concentration in each phases, in-situ in the DAC using the µ-XANES mapping technique available at the ID24 beamline (10,11). Both pieces of information were combined to retrieve the Fe partitioning coefficient between the two high-pressure phases. Our results show that Fe partitions strongly into the PPv phase, which implies a very large binary loop of coexistence of the two phases. Thus, at the core-mantle boundary pressure (135 GPa), the Pv and PPv phase always coexist for all geophysically relevant Al-(Mg,Fe)SiO3 compositions, and the Fe-content in the PPv-phase is only a few percent. References: 1. M. Murakami, K. Hirose, K. Kawamura, N. Sata, Y. Ohishi, Science 304, 855 (2004). 2. A. R. Oganov, S. Ono, Nature 430, 445 (2004). 3. S. Tateno, K. Hirose, N. Sata, Y. Ohishi, Phys. Earth Planet. Inter. 160, 319 (2007

  5. Distinct magnetism in ultrathin epitaxial NiFe2O4 films on MgAl2O4 and SrTiO3 single crystalline substrates

    NASA Astrophysics Data System (ADS)

    Foerster, Michael; Rebled, José Manuel; Estradé, Sònia; Sánchez, Florencio; Peiró, Francesca; Fontcuberta, Josep

    2011-10-01

    Spinel ferrites are being considered for advanced spintronic applications. Here, we report on the magnetic properties of ultrathin (3-37 nm) epitaxial films of NiFe2O4 (NFO) on MgAl2O4 (MAO) and SrTiO3 (STO) single crystalline substrates. It is found that NFO films on STO display superparamagnetic response down to 50 K, whereas films grown on MAO display ferrimagnetic response up to room temperature. Microstructural information indicates that this distinct response can be attributed to the different growth mechanisms of the spinel ferrite on the isostructural MAO substrate (two-dimensional growth) and the perovskite STO (Volmer-Weber three-dimensional growth). We discuss the reasons for this distinct behavior and its relevance for the integration of ferrites in epitaxial heterostructures for tunnel devices.

  6. Spin accumulation in Si channels using CoFe/MgO/Si and CoFe/AlO{sub x}/Si tunnel contacts with high quality tunnel barriers prepared by radical-oxygen annealing

    SciTech Connect

    Akushichi, T. Shuto, Y.; Sugahara, S.; Takamura, Y.

    2015-05-07

    We investigate spin injection into Si channels using three-terminal spin-accumulation (3T-SA) devices with high-quality CoFe/MgO/n-Si and CoFe/AlO{sub x}/n-Si tunnel spin-injectors whose tunnel barriers are formed by radical oxidation of Mg and Al thin films deposited on Si(100) substrates and successive annealing under radical-oxygen exposure. When the MgO and AlO{sub x} barriers are not treated by the radical-oxygen annealing, the Hanle-effect signals obtained from the 3T-SA devices are closely fitted by a single Lorentz function representing a signal due to trap spins. On the other hand, when the tunnel barriers are annealed under radical-oxygen exposure, the Hanle-effect signals can be accurately fitted by the superposition of a Lorentz function and a non-Lorentz function representing a signal due to accumulated spins in the Si channel. These results suggest that the quality improvement of tunnel barriers treated by radical-oxygen annealing is highly effective for spin-injection into Si channels.

  7. Interaction of Ta-O and perpendicular magnetic anisotropy of Ta/Pd (0-2.4 nm)/Co2FeAl0.5Si0.5/MgO/Ta structured films

    NASA Astrophysics Data System (ADS)

    You, C. Y.; Fu, H. R.; Zhang, X.; Tian, N.; Wang, P. W.

    2015-03-01

    Perpendicular magnetic anisotropy (PMA) was realized by inserting Pd layer into the stack of Ta/Pd (0-2.4 nm)/Co2FeAl0.5Si0.5/MgO/Ta. The realization of PMA is accompanied by the (Co, Fe)-O reduction at Co2FeAl0.5Si0.5/MgO interface under annealing. Without inserting Pd layer, the annealed Ta/Co2FeAl0.5Si0.5/MgO/Ta film presents an in-plane magnetization. Through X-ray photoelectron spectrometry analyzes, it was found that the oxygen was enriched at the interface of Ta/Co2FeAl0.5Si0.5. This work clarifies that the inserted Pd layer effectively blocks the diffusion of interfacial oxygen to Ta layer, achieving the beneficial redox reaction at Co2FeAl0.5Si0.5/MgO interface to realize PMA.

  8. Co{sub 2}FeAl Heusler thin films grown on Si and MgO substrates: Annealing temperature effect

    SciTech Connect

    Belmeguenai, M. Tuzcuoglu, H.; Zighem, F.; Chérif, S. M.; Moch, P.; Gabor, M. S. Petrisor, T.; Tiusan, C.

    2014-01-28

    10 nm and 50 nm Co{sub 2}FeAl (CFA) thin films have been deposited on MgO(001) and Si(001) substrates by magnetron sputtering and annealed at different temperatures. X-rays diffraction revealed polycrystalline or epitaxial growth (according to CFA(001)[110]//MgO(001)[100] epitaxial relation) for CFA films grown on a Si and on a MgO substrate, respectively. For these later, the chemical order varies from the A2 phase to the B2 phase when increasing the annealing temperature (T{sub a}), while only the A2 disorder type has been observed for CFA grown on Si. Microstrip ferromagnetic resonance (MS-FMR) measurements revealed that the in-plane anisotropy results from the superposition of a uniaxial and a fourfold symmetry term for CFA grown on MgO substrates. This fourfold anisotropy, which disappears completely for samples grown on Si, is in accord with the crystal structure of the samples. The fourfold anisotropy field decreases when increasing T{sub a}, while the uniaxial anisotropy field is nearly unaffected by T{sub a} within the investigated range. The MS-FMR data also allow for concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with T{sub a}. Finally, the FMR linewidth decreases when increasing T{sub a}, due to the enhancement of the chemical order. We derive a very low intrinsic damping parameter (1.1×10{sup −3} and 1.3×10{sup −3} for films of 50 nm thickness annealed at 615 °C grown on MgO and on Si, respectively)

  9. Phase transformation of Mg-Fe alloys

    SciTech Connect

    Yoneda, Yasuhiro; Abe, Hiroshi; Ohshima, Takeshi; Uchida, Hirohisa

    2010-05-15

    An Mg-Fe alloy system prepared through mechanical alloying (MA) was structurally analyzed. MA can produce single-phase bcc alloys using Mg concentrations up to about 15 mol %. Use of conventional average structure analysis and x-ray pair-distribution function method enabled the long-range and short-range order structures of the Mg-Fe alloys to be bridged. The substituted Mg atoms were randomly arranged in the low-Mg composition but started to have an order structure. The partially ordered Mg-Fe alloy undergoes an austenitic (cubic) to martensitic (orthorhombic) phase change, as increasing Mg composition.

  10. Ultratrace determination of arsenic in water samples by electrothermal atomic absorption spectrometry after pre-concentration with Mg-Al-Fe ternary layered double hydroxide nano-sorbent.

    PubMed

    Abdolmohammad-Zadeh, Hossein; Jouyban, Abolghasem; Amini, Roghayeh

    2013-11-15

    A selective solid phase extraction method, based on nano-structured Mg-Al-Fe(NO3(-)) ternary layered double hydroxide as a sorbent, is developed for the pre-concentration of ultra-trace levels of arsenic (As) prior to determination by electrothermal atomic absorption spectrometry. It is found that both As(III) and As(V) could be quantitatively retained on the sorbent within a wide pH range of 4-12. Accordingly, the presented method is applied to determination of total inorganic As in aqueous solutions. Maximum analytical signal of As is achieved when the pyrolysis and atomization temperatures are close to 900 °C and 2300 °C, respectively. Several variables affecting the extraction efficiency including pH, sample flow rate, amount of nano-sorbent, elution conditions and sample volume are optimized. Under the optimized conditions, the limit of detection (3Sb/m) and the relative standard deviation are 4.6 pg mL(-1) and 3.9%, respectively. The calibration graph is linear in the range of 15.0-650 pg mL(-1) with a correlation coefficient of 0.9979, sorption capacity and pre-concentration factor are 8.68 mg g(-1) and 300, respectively. The developed method is validated by the analysis of a standard reference material (SRM 1643e) and is successfully applied to the determination of ultra-trace amounts of As in different water samples.

  11. Menzerite-(Y) a New Species {(Y REE)(Ca Fe2plus)2}[(Mg Fe2plus)(Fe3plus Al)](Si3)O12 from a Felsic Granulite Parry Sound Ontario and a New Garnet End-member (Y2Ca)Mg2(SiO4)3

    SciTech Connect

    E Grew; J Marsh; M Yates; B Lazic; T Armbruster; A Locock; S Bell; M Dyar; H Bernhardt; O Medenbach

    2011-12-31

    Menzerite-(Y), a new mineral species, forms reddish brown cores, n = 1.844 (20), up to 70 {micro}m across, rimmed successively by euhedral almandine containing up to 2.7 wt% Y{sub 2}O{sub 3} and by K-feldspar in a felsic granulite on Bonnet Island in the interior Parry Sound domain, Grenville Orogenic Province, Canada. It is named after Georg Menzer (1897-1989), the German crystallographer who solved the crystal structure of garnet. Single-crystal X-ray-diffraction results yielded space group Ia3d, a = 11.9947(6) {angstrom}. An electron-microprobe analysis of the grain richest in Y (16.93 wt% Y{sub 2}O{sub 3}) gave the following formula, normalized to eight cations and 12 oxygen atoms: {l_brace}Y{sub 0.83}Gd{sub 0.01}Dy{sub 0.05}Ho{sub 0.02}Er{sub 0.07}Tm{sub 0.01}Yb{sub 0.06}Lu{sub 0.02}Ca{sub 1.37}Fe{sub 0.49}{sup 2+}Mn{sub 0.07}{r_brace} [Mg{sub 0.55}Fe{sub 0.42}{sup 2+}Fe{sub 0.58}{sup 3+}Al{sub 0.35} V{sub 0.01}Sc{sub 0.01}Ti{sub 0.08}](Si{sub 2.82}Al{sub 0.18})O{sub 12}, or {l_brace}(Y,REE)(Ca,Fe{sup 2+}){sub 2}{r_brace}[(Mg,Fe{sup 2+})(Fe{sup 3+},Al)](Si{sub 3})O{sub 12}. Synchrotron micro-XANES data gave Fe{sup 3+}/{Sigma}Fe = 0.56(10) versus 0.39(2) calculated from stoichiometry. The scattering power refined at the octahedral Y site, 17.68 epfu, indicates that a relatively light element contributes to its occupancy. Magnesium, as determined by electron-microprobe analyses, would be a proper candidate. In addition, considering the complex occupancy of this site, the average Y-O bond length of 2.0244(16) {angstrom} is in accord with a partial occupancy by Mg. The dominance of divalent cations with Mg > Fe{sup 2+} and the absence of Si at the octahedral Y site (in square brackets) are the primary criteria for distinguishing menzerite-(Y) from other silicate garnet species; the menzerite-(Y) end-member is {l_brace}Y{sub 2}Ca{r_brace}[Mg{sub 2}](Si{sub 3})O{sub 12}. The contacts of menzerite-(Y) with almandine are generally sharp and, in places, cuspate. It is

  12. SOx removal by calcined MgAlFe hydrotalcite-like materials: effect of the chemical composition and the cerium incorporation method.

    PubMed

    Cantú, Manuel; López-Salinas, Esteban; Valente, Jaime S; Montiel, Ramon

    2005-12-15

    Sulfur oxides are one of the most hazardous atmospheric pollutants since they contribute directly to acid rain formation. Consequently, stringent environmental regulations limit atmospheric SOx emissions, motivating research on efficient ways to reduce them. To supply an alternative to reduce these emissions in fluid catalytic cracking units, this study discloses efficient SOx reducing materials based on calcined MgAlFe hydrotalcite-like compounds (HT's). Thus, HT materials were synthesized by several methods including cerium addition. The adsorption of SO2 was carried out by contacting the calcined solid with a mixture of SO2 (1%) in air at 650 degrees C. It was demonstrated that the isomorphic incorporation of iron increased its reduction capability which was reflected in higher reduction rates and metal sulfate reduction grade at 550 degrees C. Moreover, when cerium was present in the iron-containing materials the saturation rate was improved, because cerium oxide promotes the oxidation of SO2 to SO3. The way cerium is incorporated influences the SO2 adsorption capacity.

  13. Vibrational spectroscopy of the phosphate mineral lazulite--(Mg, Fe)Al2(PO4)2·(OH)2 found in the Minas Gerais, Brazil.

    PubMed

    Frost, Ray L; Xi, Yunfei; Beganovic, Martina; Belotti, Fernanda Maria; Scholz, Ricardo

    2013-04-15

    This research was done on lazulite samples from the Gentil mine, a lithium bearing pegmatite located in the municipality of Mendes Pimentel, Minas Gerais, Brazil. Chemical analysis was carried out by electron microprobe analysis and indicated a magnesium rich phase with partial substitution of iron. Traces of Ca and Mn, (which partially replaced Mg) were found. The calculated chemical formula of the studied sample is: (Mg0.88, Fe0.11)Al1.87(PO4)2.08(OH)2.02. The Raman spectrum of lazulite is dominated by an intense sharp band at 1060 cm(-1) assigned to PO stretching vibrations of of tetrahedral [PO4] clusters presents into the HPO4(2-) units. Two Raman bands at 1102 and 1137 cm(-1) are attributed to both the HOP and PO antisymmetric stretching vibrations. The two infrared bands at 997 and 1007 cm(-1) are attributed to the ν1PO4(3-) symmetric stretching modes. The intense bands at 1035, 1054, 1081, 1118 and 1154 cm(-1) are assigned to the ν3PO4(3-) antisymmetric stretching modes from both the HOP and tetrahedral [PO4] clusters. A set of Raman bands at 605, 613, 633 and 648 cm(-1) are assigned to the ν4 out of plane bending modes of the PO4, HPO4 and H2PO4 units. Raman bands observed at 414, 425, 460, and 479 cm(-1) are attributed to the ν2 tetrahedral PO4 clusters, HPO4 and H2PO4 bending modes. The intense Raman band at 3402 and the infrared band at 3403 cm(-1) are assigned to the stretching vibration of the OH units. A combination of Raman and infrared spectroscopy enabled aspects of the molecular structure of the mineral lazulite to be understood.

  14. Vibrational spectroscopy of the phosphate mineral lazulite - (Mg, Fe)Al2(PO4)2·(OH)2 found in the Minas Gerais, Brazil

    NASA Astrophysics Data System (ADS)

    Frost, Ray L.; Xi, Yunfei; Beganovic, Martina; Belotti, Fernanda Maria; Scholz, Ricardo

    2013-04-01

    This research was done on lazulite samples from the Gentil mine, a lithium bearing pegmatite located in the municipality of Mendes Pimentel, Minas Gerais, Brazil. Chemical analysis was carried out by electron microprobe analysis and indicated a magnesium rich phase with partial substitution of iron. Traces of Ca and Mn, (which partially replaced Mg) were found. The calculated chemical formula of the studied sample is: (Mg0.88, Fe0.11)Al1.87(PO4)2.08(OH)2.02. The Raman spectrum of lazulite is dominated by an intense sharp band at 1060 cm-1 assigned to PO stretching vibrations of of tetrahedral [PO4] clusters presents into the HPO42- units. Two Raman bands at 1102 and 1137 cm-1 are attributed to both the HOP and PO antisymmetric stretching vibrations. The two infrared bands at 997 and 1007 cm-1 are attributed to the ν1PO43- symmetric stretching modes. The intense bands at 1035, 1054, 1081, 1118 and 1154 cm-1 are assigned to the ν3PO43- antisymmetric stretching modes from both the HOP and tetrahedral [PO4] clusters. A set of Raman bands at 605, 613, 633 and 648 cm-1 are assigned to the ν4 out of plane bending modes of the PO4, HPO4 and H2PO4 units. Raman bands observed at 414, 425, 460, and 479 cm-1 are attributed to the ν2 tetrahedral PO4 clusters, HPO4 and H2PO4 bending modes. The intense Raman band at 3402 and the infrared band at 3403 cm-1 are assigned to the stretching vibration of the OH units. A combination of Raman and infrared spectroscopy enabled aspects of the molecular structure of the mineral lazulite to be understood.

  15. Vibrational spectroscopy of the phosphate mineral lazulite--(Mg, Fe)Al2(PO4)2·(OH)2 found in the Minas Gerais, Brazil.

    PubMed

    Frost, Ray L; Xi, Yunfei; Beganovic, Martina; Belotti, Fernanda Maria; Scholz, Ricardo

    2013-04-15

    This research was done on lazulite samples from the Gentil mine, a lithium bearing pegmatite located in the municipality of Mendes Pimentel, Minas Gerais, Brazil. Chemical analysis was carried out by electron microprobe analysis and indicated a magnesium rich phase with partial substitution of iron. Traces of Ca and Mn, (which partially replaced Mg) were found. The calculated chemical formula of the studied sample is: (Mg0.88, Fe0.11)Al1.87(PO4)2.08(OH)2.02. The Raman spectrum of lazulite is dominated by an intense sharp band at 1060 cm(-1) assigned to PO stretching vibrations of of tetrahedral [PO4] clusters presents into the HPO4(2-) units. Two Raman bands at 1102 and 1137 cm(-1) are attributed to both the HOP and PO antisymmetric stretching vibrations. The two infrared bands at 997 and 1007 cm(-1) are attributed to the ν1PO4(3-) symmetric stretching modes. The intense bands at 1035, 1054, 1081, 1118 and 1154 cm(-1) are assigned to the ν3PO4(3-) antisymmetric stretching modes from both the HOP and tetrahedral [PO4] clusters. A set of Raman bands at 605, 613, 633 and 648 cm(-1) are assigned to the ν4 out of plane bending modes of the PO4, HPO4 and H2PO4 units. Raman bands observed at 414, 425, 460, and 479 cm(-1) are attributed to the ν2 tetrahedral PO4 clusters, HPO4 and H2PO4 bending modes. The intense Raman band at 3402 and the infrared band at 3403 cm(-1) are assigned to the stretching vibration of the OH units. A combination of Raman and infrared spectroscopy enabled aspects of the molecular structure of the mineral lazulite to be understood. PMID:23434550

  16. Influence of Mg component and pressure on magnetic ordering of (Mg,Fe)O

    NASA Astrophysics Data System (ADS)

    Fujii, A.; Kondo, T.; Taniguchi, T.

    2012-12-01

    (Mg,Fe)O is the second most abundant phase in the Earth's lower mantle. Knowing the fundamental properties of (Mg,Fe)O is important to understand the Earth's materials. The relation between rhombohedral distortion and antiferromagnetic ordering in FeO have been discussed, as an end member of (Mg,Fe)O. However, it does not fully understand for (Mg,Fe)O yet because its structural transition pressure is influenced by Mg component and stress condition [e.g. Zhuravlev et al., 2007]. We should also account compositional dependence on Néel temperature [Woods and Fine, 1969; Fujii et al., 2011] and spin glass-like behavior [Abbas and Hicks, 1990; Jing et al., 1993]. In this study, we investigated the compositional dependence of magnetic ordering at ambient pressure, and pressure dependence of Néel temperature up to 1.27 GPa. Superconducting Quantum Interference Device (SQUID, MPMS-7, Quantum design) was used for all magnetic measurements. We measured the temperature dependence of susceptibilities cooling with in zero field (ZFC) and in a field (FC) at ambient pressure and observed splitting between susceptibility of ZFC and FC. We confirmed that the smaller compositional dependence on Néel temperature in (Mg1-XFeX)O (X ≤ 0.60) [Fujii et al., 2011] may be explained by spin-glass transition. The transition temperature of (Mg0.40Fe0.60)O is 82 K and is close to 76 K that observed in (Mg0.23Fe0.77)0.92O [Abbas and Hicks, 1990]. The spin-glass like behavior does not affect on the Néel temperature of (Mg1-XFeX)O (X ≥ 0.70) suggested by previous work [Fujii et al., 2011] because spin-glass transition temperature would not exceed 82 K. We also measured the pressure dependence of Néel temperature of (Mg0.30Fe0.70)O, (Mg0.25Fe0.75)O and (Mg0.20Fe0.80)O using a piston cylinder type pressure cell. We calibrated pressure by superconducting transition of tin. Néel temperature of (Mg,Fe)O were increased with increasing pressure except for some measurements under non

  17. Calcioferrite with composition (Ca3.94Sr0.06)Mg1.01(Fe2.93Al1.07)(PO4)6(OH)4·12H2O

    PubMed Central

    Lafuente, Barbara; Downs, Robert T.; Yang, Hexiong; Jenkins, Robert A.

    2014-01-01

    Calcioferrite, ideally Ca4MgFe3+ 4(PO4)6(OH)4·12H2O (tetra­calcium magnesium tetrairon(III) hexakis-phosphate tetra­hydroxide dodeca­hydrate), is a member of the calcioferrite group of hydrated calcium phosphate minerals with the general formula Ca4 AB 4(PO4)6(OH)4·12H2O, where A = Mg, Fe2+, Mn2+ and B = Al, Fe3+. Calcioferrite and the other three known members of the group, montgomeryite (A = Mg, B = Al), kingsmountite (A = Fe2+, B = Al), and zodacite (A = Mn2+, B = Fe3+), usually occur as very small crystals, making their structure refinements by conventional single-crystal X-ray diffraction challenging. This study presents the first structure determination of calcioferrite with composition (Ca3.94Sr0.06)Mg1.01(Fe2.93Al1.07)(PO4)6(OH)4·12H2O based on single-crystal X-ray diffraction data collected from a natural sample from the Moculta quarry in Angaston, Australia. Calcioferrite is isostructural with montgomeryite, the only member of the group with a reported structure. The calcioferrite structure is characterized by (Fe/Al)O6 octa­hedra (site symmetries 2 and -1) sharing corners (OH) to form chains running parallel to [101]. These chains are linked together by PO4 tetra­hedra (site symmetries 2 and 1), forming [(Fe/Al)3(PO4)3(OH)2] layers stacking along [010], which are connected by (Ca/Sr)2+ cations (site symmetry 2) and Mg2+ cations (site symmetry 2; half-occupation). Hydrogen-bonding inter­actions involving the water mol­ecules (one of which is equally disordered over two positions) and OH function are also present between these layers. The relatively weaker bonds between the layers account for the cleavage of the mineral parallel to (010). PMID:24764934

  18. Interstitial Fe in MgO

    NASA Astrophysics Data System (ADS)

    Mølholt, T. E.; Mantovan, R.; Gunnlaugsson, H. P.; Svane, A.; Masenda, H.; Naidoo, D.; Bharuth-Ram, K.; Fanciulli, M.; Gislason, H. P.; Johnston, K.; Langouche, G.; Ólafsson, S.; Sielemann, R.; Weyer, G.

    2014-01-01

    Isolated 57Fe atoms were studied in MgO single-crystals by emission Mössbauer spectroscopy following implantation of 57Mn decaying to 57Fe. Four Mössbauer spectral components were found corresponding to different Fe lattice positions and/or charge states. Two components represent Fe atoms substituting Mg as Fe2+ and Fe3+, respectively; a third component is due to Fe in a strongly implantation-induced disturbed region. The fourth component, which is the focus of this paper, can be assigned to Fe at an interstitial site. Comparison of its measured isomer shift with ab initio calculations suggests that the interstitial Fe is located on, or close to, the face of the rock-salt MgO structure. To harmonize such an assignment with the measured near-zero quadrupole interaction a local motion process (cage motion) of the Fe has to be stipulated. The relation of such a local motion as a starting point for long range diffusion is discussed.

  19. Interstitial Fe in MgO

    SciTech Connect

    Mølholt, T. E. Gislason, H. P.; Ólafsson, S.; Mantovan, R.; Gunnlaugsson, H. P.; Svane, A.; Weyer, G.; Masenda, H.; Naidoo, D.; Bharuth-Ram, K.; Fanciulli, M.; Johnston, K.; Sielemann, R.

    2014-01-14

    Isolated {sup 57}Fe atoms were studied in MgO single-crystals by emission Mössbauer spectroscopy following implantation of {sup 57}Mn decaying to {sup 57}Fe. Four Mössbauer spectral components were found corresponding to different Fe lattice positions and/or charge states. Two components represent Fe atoms substituting Mg as Fe{sup 2+} and Fe{sup 3+}, respectively; a third component is due to Fe in a strongly implantation-induced disturbed region. The fourth component, which is the focus of this paper, can be assigned to Fe at an interstitial site. Comparison of its measured isomer shift with ab initio calculations suggests that the interstitial Fe is located on, or close to, the face of the rock-salt MgO structure. To harmonize such an assignment with the measured near-zero quadrupole interaction a local motion process (cage motion) of the Fe has to be stipulated. The relation of such a local motion as a starting point for long range diffusion is discussed.

  20. Effect of oxidation on interlayer exchange coupling in Fe|MgO|Fe tunnel junctions

    NASA Astrophysics Data System (ADS)

    Yang, H.-X.; Chshiev, M.; Kalitsov, A.; Schuhl, A.; Butler, W. H.

    2010-03-01

    The interlayer exchange coupling (IEC) in MgO-based magnetic tunnel junctions (MTJ) is a subject of major interest for spintronics community [1,2]. Recent experiments demonstrated that oxydation conditions strongly affect the character of the IEC in Fe/MgO/Fe(001) MTJs [3]. In order to elucidate the effect of over- and under-oxidation on the nature of the IEC in Fe|MgO|Fe MTJs, we performed systematic studies of the influence of O impurities and vacancies on the IEC using ab-initio and tight-binding approaches. We found that the O vacancies cause strong AF IEC in agreement with previous studies [2-4]. Furthermore, an additional O atom at the Fe|MgO interface makes the IEC ferromagnetic in for 3ML and above MgO thicknesses in agreement with experiment [3]. We demonstrate also that the full structural relaxation of ideal Fe|MgO|Fe MTJs may lead to the antiferromagnetic IEC. Tight-binding calculations of the IEC in the framework of the Keldysh formalism were also performed. The results obtained support our first principles calculations. [1] J. Faure-Vincent et al, Phys. Rev. Lett. 89, 107206 (2002); [2] T. Katayama et al., Appl. Phys. Lett. 89, 112503 (2006); [3] Y.F. Chiang et al, Phys. Rev. B 79, 184410 (2009); [4] M.Y. Zhuravlev et al, Phys. Rev. Lett. 94, 026806 (2005).

  1. Raman spectroscopic study of the mineral qingheiite Na2(Mn2+,Mg,Fe2+)2(Al,Fe3+)(PO4)3, a pegmatite phosphate mineral from Santa Ana pegmatite, Argentina.

    PubMed

    Frost, Ray L; Xi, Yunfei; Scholz, Ricardo; López, Andrés; Moreira, Caio; de Lena, Jorge Carvalho

    2013-10-01

    The pegmatite mineral qingheiite Na2(Mn(2+),Mg,Fe(2+))2(Al,Fe(3+))(PO4)3 has been studied by a combination of SEM and EMP, Raman and infrared spectroscopy. The studied sample was collected from the Santa Ana pegmatite, Argentina. The mineral occurs as a primary mineral in lithium bearing pegmatite, in association with beausite and lithiophilite. The Raman spectrum is characterized by a very sharp intense Raman band at 980 cm(-1) assigned to the PO4(3-) symmetric stretching mode. Multiple Raman bands are observed in the PO4(3-) antisymmetric stretching region, providing evidence for the existence of more than one phosphate unit in the structure of qingheiite and evidence for the reduction in symmetry of the phosphate units. This concept is affirmed by the number of bands in the ν4 and ν2 bending regions. No intensity was observed in the OH stretching region in the Raman spectrum but significant intensity is found in the infrared spectrum. Infrared bands are observed at 2917, 3195, 3414 and 3498 cm(-1) are assigned to water stretching vibrations. It is suggested that some water is coordinating the metal cations in the structure of qingheiite.

  2. Raman spectroscopic study of the mineral qingheiite Na2(Mn2+,Mg,Fe2+)2(Al,Fe3+)(PO4)3, a pegmatite phosphate mineral from Santa Ana pegmatite, Argentina.

    PubMed

    Frost, Ray L; Xi, Yunfei; Scholz, Ricardo; López, Andrés; Moreira, Caio; de Lena, Jorge Carvalho

    2013-10-01

    The pegmatite mineral qingheiite Na2(Mn(2+),Mg,Fe(2+))2(Al,Fe(3+))(PO4)3 has been studied by a combination of SEM and EMP, Raman and infrared spectroscopy. The studied sample was collected from the Santa Ana pegmatite, Argentina. The mineral occurs as a primary mineral in lithium bearing pegmatite, in association with beausite and lithiophilite. The Raman spectrum is characterized by a very sharp intense Raman band at 980 cm(-1) assigned to the PO4(3-) symmetric stretching mode. Multiple Raman bands are observed in the PO4(3-) antisymmetric stretching region, providing evidence for the existence of more than one phosphate unit in the structure of qingheiite and evidence for the reduction in symmetry of the phosphate units. This concept is affirmed by the number of bands in the ν4 and ν2 bending regions. No intensity was observed in the OH stretching region in the Raman spectrum but significant intensity is found in the infrared spectrum. Infrared bands are observed at 2917, 3195, 3414 and 3498 cm(-1) are assigned to water stretching vibrations. It is suggested that some water is coordinating the metal cations in the structure of qingheiite. PMID:23792288

  3. Determination of 1-naphthol and 2-naphthol from environmental waters by magnetic solid phase extraction with Fe@MgAl-layered double hydroxides nanoparticles as the adsorbents prior to high performance liquid chromatography.

    PubMed

    Zhou, Qingxiang; Lei, Man; Li, Jing; Zhao, Kuifu; Liu, Yongli

    2016-04-01

    Magnetic Fe@MgAl-layered double hydroxides (MgAl-LDHs) composite was firstly synthesized by coating MgAl-layered double hydroxides on the surface of the dispersed nanoscale zero valent irons with co-precipitation method and characterized by transmission electron microscopy and X-ray diffraction techniques. The synthesized Fe@MgAl-LDHs nanoparticles were investigated for magnetic solid phase extraction (MSPE) of 1-naphthol and 2-naphthol from the water samples. The elutent containing 1-naphthol and 2-naphthol was analyzed by high performance liquid chromatography with variable wavelength detection (HPLC-UV). Under optimal conditions, there is good linear relationship between the concentration and the peak area in the range of 0.5-200 μgL(-1) with the correlation coefficients (r(2)) above 0.998 for 1-naphthol and 2-naphthol. The limits of detection were 0.22 μgL(-1) and 0.19 μgL(-1) for 1-naphthol and 2-naphthol, respectively, and precisions were both below 2.5% (n=6). The real water analysis demonstrated that the spiked recoveries were in the range of 79.2-80.9% (n=3). All these results indicated that the developed MSPE-HPLC-UV method was proved to be an efficient tool for the analysis of naphthols.

  4. Pressure effect on the electronic structure of iron in (Mg,Fe)(Al,Si)O3 perovskite: A combined synchrotron M?ssbauer and x-ray emission spectroscopy study up to 100 GPa

    SciTech Connect

    Li, J; Sturhahn, W; Jackson, J; Struzhkin, V V; Lin, J F; Zhao, J; Mao, H K; Shen, G

    2006-01-23

    We investigated the valence and spin state of iron in an Al-bearing ferromagnesian silicate perovskite sample, (Mg{sub 0.88}Fe{sub 0.09})(Si{sub 0.94}Al{sub 0.10})O{sub 3}, at 300 K and up to 100 GPa, using diamond-anvil cells and synchrotron Moessbauer spectroscopy techniques. Under elevated pressures, our Moessbauer time spectra are sufficiently fitted by a ''three-doublet'' model, which assumes two ferrous (Fe{sup 2+}) iron types and one ferric (Fe{sup 3+}) iron type with distinct hyperfine parameters. At pressures above 20 GPa, the fraction of the ferric iron, Fe{sup 3+}/{Sigma}Fe, is about 75% and remains unchanged to the highest pressure, indicating a fixed valence state of iron within this pressure range. Between 20 and 100 GPa, the quadruple splittings of all three iron types do not change with pressure, while the isomer shift between the Fe{sup 3+} types and the Fe{sup 2+} type increases continuously with increasing pressure. In conjunction with previous x-ray emission data on the same sample, the unchanging quadruple splittings and increasing isomer shift suggest that Fe{sup 2+} undergoes a broad spin crossover towards the low-spin state at 100 GPa, while Fe{sup 3+} remains in the high-spin state. The essentially constant quadruple splittings of Fe{sup 2+} can also be taken as an indication for strong resistance against further distortion of the local iron environment after initial compression.

  5. Fabrication and characterization of spin injector using a high-quality B2-ordered-Co{sub 2}FeSi{sub 0.5}Al{sub 0.5}/MgO/Si(100) tunnel contact

    SciTech Connect

    Kawame, Yu Akushichi, Taiju; Shuto, Yusuke; Sugahara, Satoshi; Takamura, Yota

    2015-05-07

    We successfully fabricate a (100)-orientated B2-type-Co{sub 2}FeSi{sub 0.5}Al{sub 0.5} (CFSA)/MgO/Si(100) tunnel contact that is promising for an efficient spin injector for Si channels. The MgO barrier is formed by radical oxidation of an Mg thin film deposited on a Si(100) surface at room temperature and successive radical oxygen annealing at 400 °C. The CFSA electrode is grown on the MgO barrier at 400 °C by ultrahigh-vacuum molecular beam deposition, and it exhibits a (100)-orientated columnar polycrystalline structure with a high degree (63%) of B2-order. The MgO barrier near the interface of the CFSA/MgO junction is crystallized with the (100) orientation, i.e., the spin filter effect due to the MgO barrier could be expected for this junction. A three-terminal Si-channel spin-accumulation device with a CFSA/MgO/Si(100) spin injector is fabricated, and the Hanle effect of accumulated spin polarized electrons injected from this contact to the Si channel is observed.

  6. Effects of Al2O3 and MgO on Softening, Melting, and Permeation Properties of CaO-FeO-SiO2 on a Coke Bed

    NASA Astrophysics Data System (ADS)

    Ueda, Shigeru; Kon, Tatsuya; Miki, Takahiro; Kim, Sun-Joong; Nogami, Hiroshi

    2016-08-01

    In ironmaking, maintaining gas permeability in blast furnace with low coke rate operation is essential to reduce carbon emissions. The high pressure loss in the cohesive zone decreases the gas permeability and affects the productivity of blast furnace. In order to increase the gas permeability in the cohesive zone, the thickness of the cohesive layer should be decreased. For this purpose, increasing softening temperature and decreasing dripping temperature of the iron ore are desired. In this study, softening, melting, and permeation of SiO2-FeO-CaO-Al2O3-MgO on a coke bed were investigated. The oxide sample in a tablet form was heated under CO/CO2 atmosphere, and the shape of the tablet was observed. The softening and melting temperatures of the SiO2-FeO-CaO system changed with the addition of Al2O3 and MgO. Oxide tablets with and without Al2O3 softened below and above the solidus temperature, respectively. The melting temperatures varied with the ratio of CO/CO2 in the gas. The permeation temperature was independent of the melting temperature, but dependent on the wettability.

  7. Crystal structure of the mineral (Na,Ca,K){sub 2}(Ca,Na){sub 4}(Mg,Fe){sub 5}(Mg,Fe,Ti){sub 5}[Si{sub 12}Al{sub 4}O{sub 44}](F,O){sub 4}: a triclinic representative of the amphibole family

    SciTech Connect

    Rastsvetaeva, R. K. Aksenov, S. M.

    2012-05-15

    A mineral belonging to the amphibole family found at the Rothenberg paleovolcano (Eifel, Germany) was studied by single-crystal X-ray diffraction. The triclinic pseudomonoclinic unit-cell parameters are a = 5.3113(1) Angstrom-Sign , b = 18.0457(3) Angstrom-Sign ; c = 9.8684(2) Angstrom-Sign , {alpha} = 90.016(2) Degree-Sign , {beta} = 105.543(4) Degree-Sign , {gamma} = 89.985(2) Degree-Sign . The structure was solved by direct methods in sp. gr. P1 and refined to the R factor of 2.7% based on 6432 reflections with |F| > 3{sigma}(F) taking into account twinning. The mineral with the idealized formula (Na,Ca,K){sub 2}(Ca,Na){sub 4}(Mg,Fe){sub 5}(Mg,Fe,Ti){sub 5}[Si{sub 12}Al{sub 4}O{sub 44}](F,O){sub 4} has some symmetry and structural features that distinguish it from other minerals of this family.

  8. Enhancement of Biquadratic Coupling in Co/Fe/MgO/Fe(001)

    NASA Astrophysics Data System (ADS)

    Wong, Jared; Chiang, Yueh-Feng; Hoff, Andrew; Tan, Xiaojing; Li, Yan; Pi, Keyu; Hau Wang, Wei; Tom, Harry; Kawakami, Roland

    2009-03-01

    One interesting aspect of the interlayer exchange coupling (IEC) across MgO is that in addition to the bilinear coupling, a biquadratic coupling favoring 90 magnetization alignment has been observed [1, 2, 3]. We investigate IEC in Co/Fe/MgO/Fe(001) and the affects of non-ideal aspects of the MgO-heterostructure, such as interface oxidation and impurities in the MgO, via molecular beam epitaxy (MBE) synthesis and magneto-optic Kerr effect (MOKE) measurements across wedged samples. By independently varying the oxygen content of the MgO film and the Fe/MgO interface, we find that the biquadratic coupling is correlated to the interfacial oxidation. Furthermore, the temperature dependence of the biquadratic coupling exhibits a strong increase at low temperatures. Our findings strongly support the loose spin mechanism as the origin of the biquadratic coupling across MgO[4]. 1. J. Faure-Vincent, C. Tiusan, C. Bellouard, et al., Phys. Rev. Lett. 89, 107206 (2002). 2. T. Katayama, S. Yuasa, J. Velev, et al., Appl. Phys. Lett. 89, 112503 (2006). 3. E. Snoeck, P. Baules, G. BenAssayag, et al., J. Phys.: Cond. Mat. 20, 055219 (2008). 4. J. C. Slonczewski, J. Appl. Phys. 73, 5957 (1993).

  9. Investigating and engineering spin-orbit torques in heavy metal/Co{sub 2}FeAl{sub 0.5}Si{sub 0.5}/MgO thin film structures

    SciTech Connect

    Loong, Li Ming; Deorani, Praveen; Qiu, Xuepeng; Yang, Hyunsoo

    2015-07-13

    Current-induced spin-orbit torques (SOTs) have the potential to revolutionize magnetization switching technology. Here, we investigate SOT in a heavy metal (HM)/Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} (CFAS)/MgO thin film structure with perpendicular magnetic anisotropy (PMA), where the HM is either Pt or Ta. Our results suggest that both the spin Hall effect and the Rashba effect contribute significantly to the effective fields in the Pt underlayer samples. Moreover, after taking the PMA energies into account, current-induced SOT-based switching studies of both the Pt and Ta underlayer samples suggest that the two HM underlayers yield comparable switching efficiency in the HM/CFAS/MgO material system.

  10. New series of triple molybdates AgA3R(MoO4)5 (A=Mg, R=Cr, Fe; A=Mn, R=Al, Cr, Fe, Sc, In) with framework structures and mobile silver ion sublattices

    NASA Astrophysics Data System (ADS)

    Kotova, Irina Yu.; Solodovnikov, Sergey F.; Solodovnikova, Zoya A.; Belov, Dmitry A.; Stefanovich, Sergey Yu.; Savina, Aleksandra A.; Khaikina, Elena G.

    2016-06-01

    Triple molybdates AgA3R(MoO4)5 (A=Mg, R=Cr, Fe; A=Mn, R=Al, Cr, Fe, Sc, In) of the NaMg3In(MoO4)5 type were synthesized and single crystals of AgMg3R(MoO4)5 (R=Cr, Fe) were grown. In their structures, the MoO4 tetrahedra, pairs and trimers of edge-shared (Mg, R)O6 octahedra are connected by common vertices to form a 3D framework. Large framework cavities involve Ag+ cations disordered on three nearby positions with CN=3+1 or 4+1. Alternating (Mg, R)O6 octahedra and MoO4 tetrahedra in the framework form quadrangular windows penetrable for Ag+ at elevated temperatures. Above 653-673 K, the newly obtained molybdates demonstrate abrupt reduction of the activation energy to 0.4-0.6 eV. At 773 K, AgMg3Al(MoO4)5 shows electric conductivity 2.5·10-2 S/cm and Ea=0.39 eV compatible with characteristics of the best ionic conductors of the NASICON type.

  11. Effect of Fe and Mg on crystallization in granitic systems

    SciTech Connect

    Naney, M.T.; Swanson, S.E.

    1980-07-01

    Single-step and multistep undercooling experiments using both Fe, Mg-free and Fe, Mg-bearing model granitic compositions were conducted to investigate the influence of mafic components on the crystallization of granitic melts. Crystallization of granite and granodiorite compositions in the system NaAlSi/sub 3/O/sub 8/-KAlSi/sub 3/O/sub 8/-CaAl/sub 2/Si/sub 2/O/sub 8/-SiO/sub 2/-H/sub 2/O produces assemblages containing one or more of the following phases: plagioclase, alkali feldspar, quartz, silicate liquid, and vapor. The observed phase assemblages are generally in good agreement with equilibrium data reported in the literature on the same bulk compositions. With the addition of Fe and Mg to these bulk compositions six new phases participate in the equilibria (orthopyroxene, clinopyroxene, biotite, hornblende,epidote, and magnetite). However, crystalline assemblages produced in phase equilibrium and crystal growth experiments brought to the same final P-T-X/sub H/sub 2/O/ conditions are in general not equivalent. Perhaps the addition of Fe and Mg has caused a breakdown of the Si-O framework in the melt, thereby promoting the more rapid nucleation of the ino- and phyllosilicates rather than the framework silicates. Border zones of granitic plutons, commonly rich in mafic minerals, may result from the more rapid nucleation of mafic phases from the silicate liquid. These zones are thought to develop by early crystallization along the walls of the pluton. Our results suggest the mafic phases should nucleate more quickly than the feldspars and quartz and thus should enrich the early crystallization products in ferromagnesian minerals.

  12. A Sulfide Capacity Prediction Model of CaO-SiO2-MgO-FeO-MnO-Al2O3 Slags during the LF Refining Process Based on the Ion and Molecule Coexistence Theory

    NASA Astrophysics Data System (ADS)

    Yang, Xue-Min; Zhang, Meng; Shi, Cheng-Bin; Chai, Guo-Ming; Zhang, Jian

    2012-04-01

    A sulfide capacity prediction model of CaO-SiO2-MgO-FeO-MnO-Al2O3 ladle furnace (LF) refining slags has been developed based on the ion and molecule coexistence theory (IMCT). The predicted sulfide capacity of the LF refining slags has better accuracy than the measured sulfide capacity of the slags at the middle and final stages during the LF refining process. Increasing slag binary basicity, optical basicity, and the Mannesmann index can lead to an increase of the predicted sulfide capacity for the LF refining slags as well as to an increase of the sulfur distribution ratio between the slags and molten steel at the middle and final stages during the LF refining process. The calculated equilibrium mole numbers, mass action concentrations of structural units or ion couples, rather than mass percentages of components, are recommended to represent the slag composition for correlating with the sulfide capacity of the slags. The developed sulfide capacity IMCT model can calculate not only the total sulfide capacity of the slags but also the respective sulfide capacity of free CaO, MgO, FeO, and MnO in the slags. The comprehensive contribution of the combined ion couples (Ca2+ + O2-) and (Mn2+ + O2-) on the desulfurization reactions accounts for 96.23 pct; meanwhile, the average contribution of the ion couple (Fe2+ + O2-) and (Mg2+ + O2-) only has a negligible contribution as 3.13 pct and 0.25 pct during the LF refining process, respectively. The oxygen activity of bulk molten steel in LF is controlled by the [Al]-[O] equilibrium, and the oxygen activity of molten steel at the slag-metal interface is controlled by the (FeO)-[O] equilibrium. The ratio of the oxygen activity of molten steel at the slag-metal interface to the oxygen activity of bulk molten steel will decrease from 37 to 5 at the initial stage, and further decrease from 28 to 4 at the middle stage, but will maintain at a reliable constant as 5 to 14 at the final stage during the LF refining process. The

  13. Interdiffusion in the Mg-Al system and Intrinsic Diffusion in (Al3Mg2) Phase

    SciTech Connect

    Brennan, Sarah; Bermudez, Katrina; Kulkarni, Nagraj S; Sohn, Yong Ho

    2011-01-01

    Increasing use and development of lightweight Mg-alloys have led to the desire for more fundamental research in and understanding of Mg-based systems. As a strengthening component, Al is one of the most important and common alloying elements for Mg-alloys. In this study, solid-to-solid diffusion couple techniques were employed to examine the interdiffusion between pure Mg and Al. Diffusion anneals were carried out at 300 , 350 , and 400 C for 720, 360, and 240 hours, respectively. Optical and scanning electron microscopies (SEM) were employed to observe the formation of the intermetallics -Al12Mg17 and -Al3Mg2, but not -phase. Concentration profiles were determined using X-ray energy dispersive spectroscopy (XEDS). The growth constants and activation energies were determined for each intermetallic phase.

  14. Structure alterations in microporous (Mg,Fe){sub 2}Al{sub 4}Si{sub 5}O{sub 18} crystals induced by energetic heavy-ion irradiation

    SciTech Connect

    Miletich, Ronald; Diego Gatta, G.; Redhammer, Guenther J.; Burchard, Michael; Meyer, Hans-Peter; Weikusat, Christian; Rotiroti, Nicola; Glasmacher, Ulrich A.; Trautmann, Christina; Neumann, Reinhard

    2010-10-15

    The microporous framework structure of (Mg{sub 1-x}Fe{sub x}){sub 2}Al{sub 4}Si{sub 5}O{sub 18} (=cordierite) has been subject to a comparative study on the effect of structural alterations originating from exposure to high-energy heavy ions. Oriented samples (with x=0.061, 0.122, and 0.170) were irradiated with swift {sup 124}Xe, {sup 197}Au and {sup 96}Ru ions with 11.1 MeV per nucleon energy and fluences of 1x10{sup 12} and 1x10{sup 13} ions/cm{sup 2}. Irradiated and non-irradiated samples were investigated by means of X-ray diffraction, Moessbauer spectroscopy and optical absorption spectroscopy. Structural investigations reveal an essentially unchanged Al,Si ordering, which appears to be unaffected by irradiation. The most remarkable macroscopic change is the ion-beam induced colouration, which could be assigned to electronic charge transfer transitions involving the Fe cations. Moessbauer spectra indicate an increased amount of {sup [4]}Fe{sup 3+} for the irradiated sample. The most noticeable structural alteration concerns irradiation-induced dehydration of extra-framework H{sub 2}O, which is accompanied by a reduction in the molar volume by {approx}0.2 vol%. - Graphical abstract: Cordierite single-crystal specimen showing the color change from pale blue (unirradiated) to a yellowish brown layer (irradiated) after exposure to relativistic {sup 124}Xe ions at a fluence of 1x10{sup 12} ions per cm{sup 2}.

  15. Orientation relationship of eutectoid FeAl and FeAl2

    PubMed Central

    Scherf, A.; Kauffmann, A.; Kauffmann-Weiss, S.; Scherer, T.; Li, X.; Stein, F.; Heilmaier, M.

    2016-01-01

    Fe–Al alloys in the aluminium range of 55–65 at.% exhibit a lamellar microstructure of B2-ordered FeAl and triclinic FeAl2, which is caused by a eutectoid decomposition of the high-temperature Fe5Al8 phase, the so-called ∊ phase. The orientation relationship of FeAl and FeAl2 has previously been studied by Bastin et al. [J. Cryst. Growth (1978 ▸), 43, 745] and Hirata et al. [Philos. Mag. Lett. (2008 ▸), 88, 491]. Since both results are based on different crystallographic data regarding FeAl2, the data are re-evaluated with respect to a recent re-determination of the FeAl2 phase provided by Chumak et al. [Acta Cryst. (2010 ▸), C66, i87]. It is found that both orientation relationships match subsequent to a rotation operation of 180° about a 〈112〉 crystallographic axis of FeAl or by applying the inversion symmetry of the FeAl2 crystal structure as suggested by the Chumak data set. Experimental evidence for the validity of the previously determined orientation relationships was found in as-cast fully lamellar material (random texture) as well as directionally solidified material (∼〈110〉FeAl || solidification direction) by means of orientation imaging microscopy and global texture measurements. In addition, a preferential interface between FeAl and FeAl2 was identified by means of trace analyses using cross sectioning with a focused ion beam. On the basis of these habit planes the orientation relationship between the two phases can be described by (01)FeAl || (114) and [111]FeAl || [10]. There is no evidence for twinning within FeAl lamellae or alternating orientations of FeAl lamellae. Based on the determined orientation and interface data, an atomistic model of the structure relationship of Fe5Al8, FeAl and FeAl2 in the vicinity of the eutectoid decomposition is derived. This model is analysed with respect to the strain which has to be accommodated at the interface of FeAl and FeAl2. PMID:27047304

  16. Phase Equilibria of ``Cu2O''-``FeO''-CaO-MgO-Al2O3 Slags at PO2 of 10-8.5 atm in Equilibrium with Metallic Copper for a Copper Slag Cleaning Production

    NASA Astrophysics Data System (ADS)

    Henao, Hector M.; Pizarro, Claudio; Font, Jonkion; Moyano, Alex; Hayes, Peter C.; Jak, Evgueni

    2010-12-01

    Limited data are available on phase equilibria of the multicomponent slag system at the oxygen partial pressures used in the copper smelting, converting, and slag-cleaning processes. Recently, experimental procedures have been developed and have been applied successfully to characterize several complex industrial slags. The experimental procedures involve high-temperature equilibration on a substrate and quenching followed by electron probe X-ray microanalysis. This technique has been used to construct the liquidus for the “Cu2O”-“FeO”-SiO2-based slags with 2 wt pct of CaO, 0.5 wt pct of MgO, and 4.0 wt pct of Al2O3 at controlled oxygen partial pressures in equilibrium with metallic copper. The selected ranges of compositions and temperatures are directly relevant to the copper slag-cleaning processes. The new experimental equilibrium results are presented in the form of ternary sections and as a liquidus temperature vs Fe/SiO2 weight ratio diagram. The experimental results are compared with the FactSage thermodynamic model calculations.

  17. Magnetic characterization of CoFeB /MgO and CoFe /MgO interfaces

    NASA Astrophysics Data System (ADS)

    Negusse, Ezana; Lussier, A.; Dvorak, J.; Idzerda, Y. U.; Shinde, S. R.; Nagamine, Y.; Furukawa, S.; Tsunekawa, K.; Djayaprawira, D. D.

    2007-02-01

    The use of CoFeB ferromagnetic electrodes in place of CoFe has been shown to significantly increase the tunneling magnetoresistance (TMR) of MgO based magnetic tunnel junctions (MTJs). By using soft x-ray scattering techniques, we show that the behavior of the magnetic moments located at the CoFe-MgO interface are drastically different from the rest of the CoFe film, whereas the magnetic response of the CoFeB-MgO interfacial moments is coherent with the film's bulk. Our results support the view that the high TMR values observed in MgO based MTJs with CoFeB electrodes are due to the uniform magnetic response of the entire CoFeB electrode including the MgO interfacial moments.

  18. Spatial and chemical interface asymmetry in Fe/MgO/Fe(001) heterostructures

    SciTech Connect

    Palomares, F.J.; Munuera, C.; Boubeta, C. Martinez; Cebollada, A.

    2005-02-01

    The chemical nature of the different interfaces and possible segregation effects are studied in fully epitaxial Fe/MgO/Fe (001) oriented heterostructures fabricated by combined sputtering plus laser ablation deposition techniques. Auger electron spectroscopy depth profiling experiments showed that the interfaces of the MgO spacer with the Fe layers are different, the inner MgO/Fe being spatially broader and with an FeO interlayer, while that of the outer Fe/MgO is spatially narrower with no evidence of FeO formation. This spatial and chemical asymmetry is interpreted in terms of the different deposition procedures, which affect the formation of both interfaces. No Fe segregation in the MgO layers or MgO segregation in the Fe films is observed.

  19. Spin and charge transport in double-junction Fe/MgO/GaAs/MgO/Fe heterostructures

    SciTech Connect

    Wolski, S. Szczepański, T.; Dugaev, V. K.; Barnaś, J.; Landgraf, B.; Slobodskyy, T.; Hansen, W.

    2015-01-28

    We present theoretical and experimental results on tunneling current in single Fe/MgO/GaAs and double Fe/MgO/GaAs/MgO/Fe tunnel junctions. The charge and spin currents are calculated as a function of external voltage for different sets of parameters characterizing the semiconducting GaAs layer. Transport characteristics of a single Fe/MgO/GaAs junction reveal typical diode as well as spin diode features. The results of numerical calculations are compared with current-voltage characteristics measured experimentally for double tunnel junction structures, and a satisfactory agreement of the theoretical and experimental results has been achieved.

  20. Evaluation of (Mg,Fe) partitioning between silicate perovskite and magnesiowustite up to 120 GPa and 2300 K

    NASA Astrophysics Data System (ADS)

    Andrault, Denis

    2001-02-01

    The (Mg,Fe) partition coefficients between Al-(Mg,Fe)SiO3 perovskite (Pv) and (Mg,Fe)O magnesiowustite (Mw) were inferred from Pv and Mw volumes measured by X-ray diffraction (European Synchrotron Radiation Facility, Grenoble), from 22 to 120 GPa, after laser annealing up to 2300 K. The (Mg,Fe) partition coefficient is found to decrease with increasing pressure and temperature (at moderate pressures) and with the additions of Al2O3. More iron is found in perovskite than in magnesiowustite at the highest pressures and temperatures. Artifacts possibly encountered during the calculation are discussed. Perovskite was found stable up to 120 GPa and 2200 K, with iron contents (Fe/(Mg+Fe)) up to 25%. The effects of Fe and Al2O3 on the orthorhombic distortion remain reduced.

  1. Microstructural characteristics and aging response of Zn-containing Al-Mg-Si-Cu alloy

    NASA Astrophysics Data System (ADS)

    Cai, Yuan-hua; Wang, Cong; Zhang, Ji-shan

    2013-07-01

    Al-Mg-Si-Cu alloys with and without Zn addition were fabricated by conventional ingot metallurgy method. The microstructures and properties were investigated using optical microscopy (OM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), tensile test, hardness test, and electrical conductivity measurement. It is found that the as-cast Al-Mg-Si-Cu-Zn alloy is composed of coarse dendritic grains, long needle-like β/δ-AlFeSi white intermetallics, and Chinese script-like α-AlFeSi compounds. During high temperature homogenization treatment, only harmful needle-like β-AlFeSi phase undergoes fragmentation and spheroidizing at its tips, and the destructive needle-like δ-phase does not show any morphological and size changes. Phase transitions from β-AlFeSi to α-AlFeSi and from δ-AlFeSi to β-AlFeSi are also not found. Zn addition improves the aging hardening response during the former aging stage and postpones the peak-aged hardness to a long aging time. In T4 condition, Zn addition does not obviously increase the yield strength and decrease the elongation, but it markedly improves paint-bake hardening response during paint-bake cycle. The addition of 0.5wt% Zn can lead to an increment of 99 MPa in yield strength compared with the value of 69 MPa for the alloy without Zn after paint-bake cycle.

  2. Thermoelasticity of Fe3+- and Al-bearing bridgmanite: Effects of iron spin crossover

    NASA Astrophysics Data System (ADS)

    Shukla, Gaurav; Cococcioni, Matteo; Wentzcovitch, Renata M.

    2016-06-01

    We report ab initio (LDA + Usc) calculations of thermoelastic properties of ferric iron (Fe3+)- and aluminum (Al)-bearing bridgmanite (MgSiO3 perovskite), the main Earth forming phase, at relevant pressure and temperature conditions and compositions. Three coupled substitutions, namely, [Al]Mg-[Al]Si, [Fe3+]Mg-[Fe3+]Si, and [Fe3+]Mg-[Al]Si have been investigated. Aggregate elastic moduli and sound velocities are successfully compared with limited experimental data available. In the case of [Fe3+]Mg-[Fe3+]Si substitution, the high-spin (S = 5/2) to low-spin (S = 1/2) crossover in [Fe3+]Si induces a volume collapse and elastic anomalies across the transition region. However, the associated anomalies should disappear in the presence of aluminum in the most favorable substitution, i.e., [Fe3+]Mg-[Al]Si. Calculated elastic properties along a lower mantle model geotherm suggest that the elastic behavior of bridgmanite with simultaneous substitution of Fe2O3 and Al2O3 in equal proportions or with Al2O3 in excess should be similar to that of (Mg,Fe2+)SiO3 bridgmanite. However, excess of Fe2O3 should produce elastic anomalies in the crossover pressure region.

  3. Strengthening of Al and Al-Mg alloy wires by melt inoculation with Al/MgB2 nanocomposite

    NASA Astrophysics Data System (ADS)

    Florián-Algarín, David; Marrero, Raúl; Padilla, Alexandra; Suárez, Oscar Marcelo

    2015-12-01

    This study hinges on the feasibility of strengthening Al and Al-Mg wires by adding Al nanocomposite pellets containing MgB2 nanoparticles into the melt upon fabrication. These MgB2 nanoparticles were obtained by fragmentation using a high-energy ball mill, and were, afterward, mechanically alloyed with pure aluminum. The resulting MgB2/Al nanocomposite pellets were sintered at 260°C to be subsequently added into molten aluminum and an Al-Mg alloy melt. Cold rolling intercalated with stepwise annealing allowed the fabrication of 1 mm diameter wires with a final area reduction of 96%. Mechanical and physical properties of the treated wire specimens were compared to those of similarly processed pure aluminum wire. The ultimate tensile strength of the treated wires increased approximately double fold with respect to untreated wires at the expense of some loss in electrical conductivity.

  4. Removal of phosphate from water using six Al-, Fe-, and Al-Fe-modified bentonite adsorbents.

    PubMed

    Shanableh, Abdallah M; Elsergany, Moetaz M

    2013-01-01

    This study was part of a larger effort that involves evaluating alternatives to upgrading secondary treatment systems in the United Arab Emirates for the removal of nutrients. In this study, six modified bentonite (BNT) phosphate adsorbents were prepared using solutions that contained hydroxy-polycations of aluminum (Al-BNT), iron (Fe-BNT), and mixtures of aluminum and iron (Al-Fe-BNT). The adsorption kinetics and capacities of the six adsorbents were evaluated, and the adsorbents were used to remove phosphorus from synthetic phosphate solutions and from treated wastewater. The experimental adsorption kinetics results were well represented by the pseudo-second-order kinetic model, with R(2) values ranging from 0.99 to 1.00. Similarly, the experimental equilibrium adsorption results were well represented by the Freundlich and Langmuir isotherms, with R(2) values ranging from 0.98 to 1.00. The adsorption capacities of the adsorbents were dependent on the BNT preparation conditions; the types, quantities and combination of metals used; BNT particle size; and adsorption pH. The Langmuir maximum adsorption capacities of the six adsorbents ranged from 8.9-14.5 mg P/g-BNT. The results suggested that the BNT preparations containing Fe alone or in combination with Al achieved higher adsorption capacities than the preparations containing only Al. However, the Al-BNT preparations exhibited higher adsorption rates than the Fe-BNT preparation. Three of the six adsorbents were used to remove phosphate from secondarily treated wastewater samples, and the removal results were comparable to those obtained using synthetic phosphate solutions. The BNT adsorbents also exhibited adequate settling characteristics and significant regeneration potential.

  5. Thermodynamic modeling of non-ideal mineral-fluid equilibria in the system Si-Al-Fe-Mg-Ca-Na-K-H-O-Cl at elevated temperatures and pressures: Implications for hydrothermal mass transfer in granitic rocks

    NASA Astrophysics Data System (ADS)

    Dolejš, David; Wagner, Thomas

    2008-01-01

    We present the results of thermodynamic modeling of fluid-rock interaction in the system Si-Al-Fe-Mg-Ca-Na-H-O-Cl using the GEM-Selektor Gibbs free energy minimization code. Combination of non-ideal mixing properties in solids with multicomponent aqueous fluids represents a substantial improvement and it provides increased accuracy over existing modeling strategies. Application to the 10-component system allows us to link fluid composition and speciation with whole-rock mineralogy, mass and volume changes. We have simulated granite-fluid interaction over a wide range of conditions (200-600 °C, 100 MPa, 0-5 m Cl and fluid/rock ratios of 10-2-104) in order to explore composition of magmatic fluids of variable salinity, temperature effects on fluid composition and speciation and to simulate several paths of alteration zoning. At low fluid/rock ratios (f/r) the fluid composition is buffered by the silicate-oxide assemblage and remains close to invariant. This behavior extends to a f/r of 0.1 which exceeds the amount of exsolved magmatic fluids controlled by water solubility in silicate melts. With increasing peraluminosity of the parental granite, the Na-, K- and Fe-bearing fluids become more acidic and the oxidation state increases as a consequence of hydrogen and ferrous iron transfer to the fluid. With decreasing temperature, saline fluids become more Ca- and Na-rich, change from weakly acidic to alkaline, and become significantly more oxidizing. Large variations in Ca/Fe and Ca/Mg ratios in the fluid are a potential geothermometer. The mineral assemblage changes from cordierite-biotite granites through two-mica granites to chlorite-, epidote- and zeolite-bearing rocks. We have carried out three rock-titration simulations: (1) reaction with the 2 m NaCl fluid leads to albitization, chloritization and desilication, reproducing essential features observed in episyenites, (2) infiltration of a high-temperature fluid into the granite at 400 °C leads to hydrolytic

  6. Atomistically informed solute drag in Al Mg

    NASA Astrophysics Data System (ADS)

    Zhang, F.; Curtin, W. A.

    2008-07-01

    Solute drag in solute-strengthened alloys, caused by diffusion of solute atoms around moving dislocations, controls the stress at deformation rates and temperatures useful for plastic forming processes. In the technologically important Al-Mg alloys, the solute drag stresses predicted by classical theories are much larger than experiments, which is resolved in general by eliminating the singularity of the dislocation core via Peierls-Nabarro-type models. Here, the drag stress versus dislocation velocity is computed numerically using a realistic dislocation core structure obtained from an atomistic model to investigate the role of the core and obtain quantitative stresses for comparison with experiment. The model solves a discrete diffusion equation in a reference frame moving with the dislocation, with input solute enthalpies and diffusion activation barriers in the core computed by or estimated from atomistic studies. At low dislocation velocities, the solute drag stress is controlled by bulk solute diffusion because the core diffusion occurs too quickly. In this regime, the drag stress can be obtained using a Peierls-Nabarro model with a core spreading parameter tuned to best match the atomistic models. At intermediate velocities, both bulk and core diffusion can contribute to the drag, leading to a complex stress-velocity relationship showing two peaks in stress. At high velocities, the drag stress is controlled solely by diffusion within and across the core. Like the continuum models, the drag stress is nearly linear in solute concentration. The Orowan relationship is used to connect dislocation velocity to deformation strain rate. Accounting for the dependence of mobile dislocation density on stress, the simulations are in good agreement with experiments on Al-Mg alloys over a range of concentrations and temperatures.

  7. Cross sections for the production of residual nuclides by low- and medium-energy protons from the target elements C, N, O, Mg, Al, Si, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, Sr, Y, Zr, Nb, Ba and Au

    NASA Astrophysics Data System (ADS)

    Michel, R.; Bodemann, R.; Busemann, H.; Daunke, R.; Gloris, M.; Lange, H.-J.; Klug, B.; Krins, A.; Leya, I.; Lüpke, M.; Neumann, S.; Reinhardt, H.; Schnatz-Büttgen, M.; Herpers, U.; Schiekel, Th.; Sudbrock, F.; Holmqvist, B.; Condé, H.; Malmborg, P.; Suter, M.; Dittrich-Hannen, B.; Kubik, P.-W.; Synal, H.-A.; Filges, D.

    1997-07-01

    Cross sections for residual nuclide production by p-induced reactions were measured from thresholds up to 2.6 GeV using accelerators at CERN/Geneve, IPN/Orsay, KFA/Jülich, LANL/Los Alamos, LNS/Saclay, PSI/Villigen, TSL/Uppsala, LUC/Louvain La Neuve. The target elements C, N, O, Mg, Al, Si, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, Sr, Y, Zr, Nb, Ba and Au were investigated. Residual nuclides were measured by X- and γ-spectrometry and by Accelerator Mass Spectrometry (AMS). The measured cross sections were corrected for interfering secondary particles in experiments with primary proton energies above 200 MeV. Our consistent database covers presently ca 550 nuclear reactions and contains nearly 15000 individual cross sections of which about 10000 are reported here for the first time. They provide a basis for model calculations of the production of cosmogenic nuclides in extraterrestrial matter by solar and galactic cosmic ray protons. They are of importance for many other applications in which medium energy nuclear reactions have to be considered ranging from astrophysics over space and environmental sciences to accelerator technology and accelerator-based nuclear waste transmutation and energy amplification. The experimental data are compared with theoretical ones based on calculations using an INC/E model in form of the HETC/KFA2 code and on the hybrid model of preequilibrium reactions in form of the AREL code.>

  8. Influence of hot isostatic pressing on the structure and properties of an innovative low-alloy high-strength aluminum cast alloy based on the Al-Zn-Mg-Cu-Ni-Fe system

    NASA Astrophysics Data System (ADS)

    Akopyan, T. K.; Padalko, A. G.; Belov, N. A.

    2015-11-01

    Hot isostatic pressing (HIP) is applied for treatment of castings of innovative low-ally high-strength aluminum alloy, nikalin ATs6N0.5Zh based on the Al-Zn-Mg-Cu-Ni-Fe system. The influence of HIP on the structure and properties of castings is studied by means of three regimes of barometric treatment with different temperatures of isometric holding: t 1 = 505 ± 2°C, p 1 = 100 MPa, τ1 = 3 h (HIP1); t 2 = 525 ± 2°C, p 2 = 100 MPa, τ2 = 3 h (HIP2); and t 3 = 545 ± 2°C, p 3 = 100 MPa, τ3 = 3 h (HIP3). It is established that high-temperature HIP leads to actually complete elimination of porosity and additional improvement of the morphology of second phases. Improved structure after HIP provides improvement properties, especially of plasticity. In particular, after heat treatment according of regime HIP2 + T4 (T4 is natural aging), the alloy plasticity is improved by about two times in comparison with the initial state (from ~6 to 12%). While applying regime HIP3 + T6 (T6 is artificial aging for reaching the maximum strength), the plasticity has improved by more than three times in comparison with the initial state, as after treatment according to regimes HIP1 + T6 and HIP2 + T6 (from ~1.2 to ~5.0%), which are characterized by a lower HIP temperature.

  9. Correlation of the structural properties of a Pt seed layer with the perpendicular magnetic anisotropy features of full Heusler-based Co2FeAl/MgO/Co2Fe6B2 junctions via a 12-inch scale Si wafer process

    NASA Astrophysics Data System (ADS)

    Chae, Kyo-Suk; Lee, Du-Yeong; Shim, Tae-Hun; Hong, Jin-Pyo; Park, Jea-Gun

    2013-10-01

    We elucidated the interfacial-perpendicular magnetic anisotropy (i-PMA) features of full Heusler-based Co2FeAl/MgO/Co2Fe6B2 magnetic-tunnel-junctions as functions of the structural properties of the Pt seed layer including its thickness and ex situ annealing temperature. All of the samples were prepared in a 12-inch silicon wafer process for real industry applications. The observations of the M-H loops emphasize that a thinner Pt seed layer and a high ex situ annealing temperature enhance the surface roughness of the seed layer, providing better i-PMA characteristics. HR-TEM images of the samples were evaluated to understand the structural effects of thin and thick Pt seed layers.

  10. Magnetism in Fe4Al13 and related FeAl intermetallics

    NASA Astrophysics Data System (ADS)

    Chi, Ji; Li, Yang; Gou, Weiping; Goruganti, V.; Rathnayaka, K. D. D.; Ross, Joseph H., Jr.

    2006-03-01

    We report the results of an experimental study of FeAl alloys, including Fe4Al13, FeAl2 and Fe2Al5. By using NMR, dc magnetic susceptibility, and specific heat, we found that Fe4Al13 and Fe2Al5 are non-magnetic with some dilute magnetic moments, while FeAl2 can be characterized as a concentrated local moment system. Fe4Al13 is a decagonal quasicrystal approximant with 102 atoms in its unit cell. The ^27Al NMR spin-lattice relaxation indicates a very narrow pseudogap in the electronic density of states [g(E)] in the vicinity of the Fermi energy. The observations could be fit assuming a parabolic variation of g(E), consistent with observations in other quasicrystals and approximants. NMR lineshape measurements also agree with this analysis, and show that the system is dilute-magnetic, in strong contrast to the FeAl2 ordered intermetallic. We use specific heat to analyze the dilute moment density. This work was supported by the Robert A. Welch Foundation, Grant No. A-1526, by the National Science Foundation (DMR-0103455), and by Texas A&M University through the Telecommunications and Informatics Task Force.

  11. Hillesheimite, (K,Ca,□)2(Mg,Fe,Ca,□)2[(Si,Al)13O23(OH)6](OH) · 8H2O, a new phyllosilicate mineral of the Günterblassite group

    NASA Astrophysics Data System (ADS)

    Chukanov, N. V.; Zubkova, N. V.; Pekov, I. V.; Belakovskiy, D. I.; Schüller, W.; Ternes, B.; Blass, G.; Pushcharovsky, D. Yu.

    2013-12-01

    A new mineral, hillesheimite, has been found in the Graulai basaltic quarry, near the town of Hillesheim, the Eifel Mountains, Rhineland-Palatinate (Rheinland-Pfalz), Germany. It occurs in the late assemblage comprising nepheline, augite, fluorapatite, magnetite, perovskite, priderite, götzenite, lamprophyllite-group minerals, and åkermanite. Colorless flattened crystals of hillesheimite reaching 0.2 × 1 × 1.5 mm in size and aggregates of the crystals occur in miarolitic cavities in alkali basalt. The mineral is brittle, with Mohs' hard-ness 4. Cleavage is perfect parallel to (010) and distinct on (100) and (001). D calc = 2.174 g/cm3, D meas = 2.16(1) g/cm3. IR spectrum is given. Hillesheimite is biaxial (-), α = 1.496(2), β = 1.498(2), γ = 1.499(2), 2 V meas = 80°. The chemical composition (electron microprobe, mean of 4 point analyses, H2O determined from structural data, wt %) is as follows: 0.24 Na2O, 4.15 K2O, 2.14 MgO, 2.90 CaO, 2.20 BaO, 2.41 FeO, 15.54 Al2O3, 52.94 SiO2, 19.14 H2O, total is 101.65. The empirical formula is: K0.96Na0.08Ba0.16Ca0.56Mg0.58Fe{0.37/2+}[Si9.62Al3.32O23(OH)6][(OH)0.82(H2O)0.18] · 8H2O. The crystal structure has been determined from X-ray single-crystal diffraction data, R = 0.1735. Hillesheimite is orthorhombic, space group Pmmn, the unit-cell dimensions are: a = 6.979(11), b = 37.1815(18), c = 6.5296(15) Å; V=1694(3) Å3, Z = 2. The crystal structure is based on the block [(Si,Al)13O25(OH)4] consisting of three single tetrahedral layers linked via common vertices and is topologically identical to the triple layers in günterblassite and umbrianite. The strong reflections [ d Å ( I %)] in the X-ray powder diffraction pattern are: 6.857(58), 6.545(100), 6.284(53), 4.787(96), 4.499(59), 3.065(86), 2.958(62), 2.767(62). The mineral was named after its type locality. Type specimens are deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, registration number 4174/1.

  12. Enhancing phosphate adsorption by Mg/Al layered double hydroxide functionalized biochar with different Mg/Al ratios.

    PubMed

    Li, Ronghua; Wang, Jim J; Zhou, Baoyue; Awasthi, Mukesh Kumar; Ali, Amjad; Zhang, Zengqiang; Gaston, Lewis A; Lahori, Altaf Hussain; Mahar, Amanullah

    2016-07-15

    Mg/Al ratio plays a significant role for anion adsorption by Mg/Al-layered double hydroxides (Mg/Al-LDHs) modified biochar. In this study, Mg/Al-LDHs biochar with different Mg/Al ratios (2, 3, 4) were prepared by co-precipitation for phosphate removal from aqueous solution. Factors on phosphate adsorption including Mg/Al ratio, pH, and the presence of other inorganic anions were investigated through batch experiments. Increasing Mg/Al ratio in the Mg/Al-LDHs biochar composites generally enhanced phosphate adsorption with Langmuir adsorption maximum calculated at 81.83mg phosphorous (P) per gram of 4:1Mg/Al-LDHs biochar at pH3.0. The adsorption process was best described by the pseudo-second-order kinetic model. Solution pH had greater effects on the phosphate adsorption by Mg/Al LDHs biochar composites with lower Mg/Al ratios. The presence of other inorganic anions decreased the phosphate adsorption efficiency in the order of F(-) > SO4(2-) > NO2(-) >Cl(-). Phosphate adsorption mechanism involves ion exchange, electrostatic attraction and surface inner-sphere complex formation. Overall, Mg/Al-LDHs biochar composites offer a potential alternative of carbon-based adsorbent for phosphate removal from aqueous solution. PMID:27058131

  13. Dipole defects in Al2O3:Mg,Cr.

    PubMed

    Blak, A R; Gobbi, V; Ayres, F

    2002-01-01

    In this work, dipole defects are investigated applying the thermally stimulated depolarisation currents (TSDC) technique. The TSDC spectra of Al2O3 doped with Mg and Cr show two bands centred at 230 K and 250 K, respectively. The maximum intensity of the bands increases linearly with the polarisation field, a typical behaviour of defects with dipole origin. An increase of the band at 250 K with gamma irradiation has been observed and a thermal decrease of the bands for heat treatments between 1000 K and 1400 K. Above this temperature the bands are partially recovered. Impurity neutron activation analysis shows that magnesium. chromium and iron content varies from 15 to 60 ppm. Optical absorption (AO) measurements show a broad band centred in 2.6 eV (21000 cm(-1)) associated with trapped holes localised on an O- ion adjacent to a cation site which is deficient in positive charge. It has been assumed that a substitutional Mg2+ ion occupies the cation site near a trapped hole on one of the six oxygen ions surrounding the magnesium impurity giving rise to the dipole responsible for the observed TSDC bands. Calculations carried out through defect simulation methods confirm that the probability of Al3+ being replaced by Mg2+ is higher than Mn2+, Co2+, Fe2+ and Cr2+. PMID:12382829

  14. The half-metallicity of LiMgPdSn-type quaternary Heusler alloys FeMnScZ (Z=Al, Ga, In): A first-principle study

    SciTech Connect

    Gao, Y. C.; Gao, X.

    2015-05-15

    Based on the first-principles calculations, quaternary Heusler alloys FeMnScZ (Z=Al, Ga, In) including its phase stability, band gap, the electronic structures and magnetic properties has been studied systematically. We have found that, in terms of the equilibrium lattice constants, FeMnScZ (Z=Al, Ga, In) are half-metallic ferrimagnets, which can sustain the high spin polarization under a very large amount of lattice distortions. The half-metallic band gap in FeMnScZ (Z=Al, Ga, In) alloys originates from the t{sub 1u}-t{sub 2g} splitting instead of the e{sub u}-t{sub 1u} splitting. The total magnetic moments are 3μB per unit cell for FeMnScZ (Z=Al, Ga, In) alloys following the Slater–Pauling rule with the total number of valence electrons minus 18 rather than 24. According to the study, the conclusion can be drawn that all of these compounds which have a negative formation energy are possible to be synthesized experimentally.

  15. Modulus measurements in ordered Co-Al, Fe-Al, and Ni-Al alloys

    NASA Technical Reports Server (NTRS)

    Harmouche, M. R.; Wolfenden, A.

    1985-01-01

    The composition and/or temperature dependence of the dynamic Young's modulus for the ordered B2 Co-Al, Fe-Al, and Ni-Al aluminides has been investigated using the piezoelectric ultrasonic composite oscillator technique (PUCOT). The modulus has been measured in the composition interval 48.49 to 52.58 at. pct Co, 50.87 to 60.2 at. pct Fe, and 49.22 to 55.95 at. pct Ni for Co-Al, Fe-Al, and Ni-Al, respectively. The measured values for Co-Al are in the temperature interval 300 to 1300 K, while those for the other systems are for ambient temperature only. The data points show that Co-Al is stiffer than Fe-Al, which is stiffer than Ni-Al. The data points for Fe-Al and Ni-Al are slightly higher than those reported in the literature.

  16. Atomic data from the iron project. 3: Rate coefficients for electron impact excitation of boron-like ions: Ne VI, Mg VIII, Al IX, Si X, S XII, Ar XIV, Ca XVI and Fe XXII

    NASA Technical Reports Server (NTRS)

    Zhang, Hong Lin; Graziani, Mark; Pradhan, Anil K.

    1994-01-01

    Collison strengths and maxwellian averaged rate coefficients have been calculated for the 105 transitions among all 15 fine structure levels of the 8 LS terms 2s(sup 2) 2 P(P-2(sup 0 sub 1/, 3/2)), 2s2p(sup 2)(P-4(sub 1/2,3/2,5/2), D-2(sub 3/2, 5/2), S-2(sub 1/2), P-2(sub 1/2, 3/2)), 2p(sup 3)(S-4(sup 0)(sub 3/2), D-2(sup 0 sub 3/2, 5/2), P-2(sup 0 sub 1/2, 3/2)) in highly- charged B-like Ne, Mg, Al, Si, S, Ar, Ca and Fe. Rate coefficients have been tabulated at a wide range of temperatures, depending on the ion charge and abundance in plasma sources. Earlier work for O IV has also been extended to include the high temperature range. A brief discussion of the calculations, sample results, and comparison with earlier works is also given. While much of the new data should be applicable to UV spectral diagnostics, the new rates for the important ground state fine structure transition P-2(sup 0 sub 1/2)-P-2(sup 0 sub 3/2) should result in significant revision of the IR cooling rates in plasmas where B-like ions are prominent constituents, since the new rate coefficients are generally higher by several factors compared with the older data.

  17. Localized Corrosion Behavior of Al-Si-Mg Alloys Used for Fabrication of Aluminum Matrix Composites

    NASA Astrophysics Data System (ADS)

    Pech-Canul, M. A.; Giridharagopal, R.; Pech-Canul, M. I.; Coral-Escobar, E. E.

    2013-12-01

    The relationship between microstructure and localized corrosion behavior in neutral aerated chloride solutions was investigated with SEM/EDAX, conventional electrochemical techniques, and with scanning Kelvin probe force microscopy (SKPFM) for two custom-made alloys with Si/Mg molar ratios of 0.12 and 0.49. In this order, Al3Fe, Al3Mg2, and Mg2Si intermetallics were identified in the first alloy and Al(FeMn)Si and Mg2Si particles in the second one. Anodic polarization curves and corrosion morphology showed that the alloy with higher Si/Mg molar ratio exhibited a better corrosion performance and evidence was shown that it had a more corrosion-resistant passive film. The corrosion process for both alloys in aerated 0.1 M NaCl solutions was localized around the Fe-rich intermetallics. They acted as local cathodes and produced dissolution of the aluminum matrix surrounding such particles. Mg2Si and Al3Mg2 exhibited anodic behavior. SKPFM was successfully used to map the Volta potential distribution of main intermetallics. The localized corrosion behavior was correlated with a large Volta potential difference between the Fe-rich intermetallics and the matrix. After immersion in the chloride solution, such Volta potential difference decreased.

  18. Mechanical Properties of High Strength Al-Mg Alloy Sheet

    NASA Astrophysics Data System (ADS)

    Choi, Bong-Jae; Hong, Kyung-Eui; Kim, Young-Jig

    The aim of this research is to develop the high strength Al alloy sheet for the automotive body. For the fabrication Al-Mg alloy sheet, the composition of alloying elements was designed by the properties database and CALPHAD (Calculation Phase Diagram) approach which can predict the phases during solidification using thermodynamic database. Al-Mg alloys were designed using CALPHAD approach according to the high content of Mg with minor alloying elements. After phase predictions by CALPHAD, designed Al-Mg alloys were manufactured. Addition of Mg in Al melts were protected by dry air/Sulphur hexafluoride (SF6) mixture gas which can control the severe Mg ignition and oxidation. After rolling procedure of manufactured Al-Mg alloys, mechanical properties were examined with the variation of the heat treatment conditions.

  19. Effect of delayed aging on mechanical properties of an Al-Cu-Mg alloy

    SciTech Connect

    Ravindranathan, S.P.; Kashyap, K.T.; Kumar, S.R.; Ramachandra, C.; Chatterji, B.

    2000-02-01

    The effect of delayed aging on mechanical properties is characteristically found in Al-Mg-Si alloys. Delayed aging refers to the time elapsed between solutionizing and artificial aging. Delayed aging leads to inferior properties. This effect was investigated in an Al-Cu-Mg alloy (AU2GN) of nominal composition Al-2Cu-1.5Mg-1Fe-1Ni as a function of delay. This alloy also showed a drop in mechanical properties with delay. The results are explained on the basis of Pashley's kinetic model to qualitatively explain the evolution of a coarse precipitate structure with delay. It is found that all the results of delayed aging in the Al-Cu-Mg alloys are similar to those found in Al-Mg-Si alloys.

  20. The mechanical properties of FeAl

    SciTech Connect

    Baker, I.; George, E.P.

    1996-12-31

    Only in the last few years has progress been made in obtaining reproducible mechanical properties data for FeAl. Two sets of observations are the foundation of this progress. The first is that the large vacancy concentrations that exist in FeAl at high temperature are easily retained at low temperature and that these strongly affect the low-temperature mechanical properties. The second is that RT ductility is adversely affected by water vapor. Purpose of this paper is not to present a comprehensive overview of the mechanical properties of FeAl but rather to highlight our understanding of key phenomena and to show how an understanding of the factors which control the yield strength and fracture behavior has followed the discovery of the above two effects. 87 refs, 9 figs.

  1. Interdiffusion and Intrinsic Diffusion in the Mg-Al System

    SciTech Connect

    Brennan, Sarah; Bermudez, Katrina; Sohn, Yong Ho; Kulkarni, Nagraj S

    2012-01-01

    Solid-to-solid diffusion couples were assembled and annealed to examine the diffusion between pure Mg (99.96%) and Al (99.999%). Diffusion anneals were carried out at 300 , 350 , and 400 C for 720, 360, and 240 hours, respectively. Optical and scanning electron microscopes were utilized to identify the formation of the intermetallic phases, -Al12Mg17 and -Al3Mg2 and absence of the -phase in the diffusion couples. Thicknesses of the -Al12Mg17 and -Al3Mg2 phases were measured and the parabolic growth constants were calculated to determine the activation energies for the growth, 165 and 86 KJ/mole, respectively. Concentration profiles were determined with electron microprobe analysis using pure elemental standards. Composition-dependent interdiffusion coefficients in Mg-solid solution, -Al12Mg17 and - Al3Mg2 and Al-solid solutions were calculated based on the Boltzmann-Matano analysis. Average effective interdiffusion coefficients for each phase were also calculated, and the magnitude was the highest for the -Al3Mg2 phase, followed by -Al12Mg17, Al-solid solution and Mg-solid solution. Intrinsic diffusion coefficients based on Huemann s analysis (e.g., marker plane) were determined for the ~38 at.% Mg in the -Al3Mg2 phase. Activation energies and the pre-exponential factors for the inter- and intrinsic diffusion coefficients were calculated for the temperature range examined. The -Al3Mg2 phase was found to have the lowest activation energies for growth and interdiffusion among all four phases studied. At the marker location in the -Al3Mg2 phase, the intrinsic diffusion of Al was found to be faster than that of Mg. Extrapolations of the impurity diffusion coefficients in the terminal solid solutions were made and compared to the available self- and impurity diffusion data from literature. Thermodynamic factor, tracer diffusion coefficients and atomic mobilities at the marker plane composition were approximated using available literature values of Mg activity in the -Al

  2. The molar volume of cubic garnets in the system SiO2-Al2O3-TiO2-Fe2O3-Cr2O3-FeO-MnO-MgO-CaO-Na2O

    NASA Astrophysics Data System (ADS)

    Hamecher, E. A.; Antoshechkina, P. M.; Ghiorso, M. S.; Asimow, P. D.

    2012-12-01

    Garnet is a critical phase that controls major and trace element partitioning at pressures above ~3 GPa during partial melting of the Earth's upper mantle. A molar volume model is calibrated for cubic garnets (space group Ia3d) in the oxide system listed in the title. This model and a recent calibration of spinel molar volume (Hamecher et al., in press, CMP) will be used in calibration of thermodynamic activity-composition models of garnet and pyroxene solid solutions. The activity and molar volume models will be incorporated into the next generation MELTS (Ghiorso & Sack, 1995, CMP) model, xMELTS. A new garnet volume model calibrated with recent in situ high-P, T diffraction data is crucial for accurately modeling key mineralogical transitions in the mantle, e.g., the spinel-garnet transition and the mantle transition zone. Above 5 GPa a majorite component is an essential part of any thermodynamic model of mantle garnets, which to be useful must accurately predict garnet stability with respect to spinel, pyroxene, perovskites, and melt. Our model system contains nine independent end members: Ca3Al2Si3O12, Mg3Al2Si3O12, Fe2+3Al2Si3O12, Mg3Cr2Si3O12, Mg3Fe3+2Si3O12, Mn3Al2Si3O12, Na2(MgSi2)Si3O12, Mg3(TiMg)Si3O12, and cubic majorite component Mg3(MgSi)Si3O12. An inclusive set of end-member components is formed by linear combinations of these explicit end members. Approximately 950 published X-ray diffraction experiments performed on garnets at ambient and in situ high-P, T conditions are used to calibrate end-member equations of state and an excess volume model for this system. Optimal values of the bulk modulus and its pressure derivative are obtained by analyzing published compression and/or ultrasonic data for the end members for which such studies exist; for other end members, density functional theory results are used. For any cubic garnet in this chemical system, the model molar volume is obtained by adding excess volume terms to a linear combination of the

  3. Melting, Processing, and Properties of Disordered Fe-Al and Fe-Al-C Based Alloys

    NASA Astrophysics Data System (ADS)

    Satya Prasad, V. V.; Khaple, Shivkumar; Baligidad, R. G.

    2014-09-01

    This article presents a part of the research work conducted in our laboratory to develop lightweight steels based on Fe-Al alloys containing 7 wt.% and 9 wt.% aluminum for construction of advanced lightweight ground transportation systems, such as automotive vehicles and heavy-haul truck, and for civil engineering construction, such as bridges, tunnels, and buildings. The melting and casting of sound, porosity-free ingots of Fe-Al-based alloys was accomplished by a newly developed cost-effective technique. The technique consists of using a special flux cover and proprietary charging schedule during air induction melting. These alloys were also produced using a vacuum induction melting (VIM) process for comparison purposes. The effect of aluminum (7 wt.% and 9 wt.%) on melting, processing, and properties of disordered solid solution Fe-Al alloys has been studied in detail. Fe-7 wt.% Al alloy could be produced using air induction melting with a flux cover with the properties comparable to the alloy produced through the VIM route. This material could be further processed through hot and cold working to produce sheets and thin foils. The cold-rolled and annealed sheet exhibited excellent room-temperature ductility. The role of carbon in Fe-7 wt.% Al alloys has also been examined. The results indicate that Fe-Al and Fe-Al-C alloys containing about 7 wt.% Al are potential lightweight steels.

  4. Magnetic properties of epitaxial discontinuous Fe/MgO multilayers.

    PubMed

    García-García, A; Pardo, J A; Strichovanec, P; Magén, C; Vovk, A; De Teresa, J M; Kakazei, G N; Pogorelov, Yu G; Golub, V; Salyuk, O; Morellón, L; Algarabel, P A; Ibarra, M R

    2012-09-01

    We report magnetic, dynamic and transport properties of discontinuous metal-insulator multilayers Fe/MgO grown on amorphous Corning glass and single-crystalline MgO (001) substrates. The films of structure Substrate/MgO (3 nm)/[Fe (0.6 nm)/MgO (3.0 nm)] x 10 were prepared in ultra-high vacuum conditions using Pulsed Laser Deposition. It was shown that conditions of epitaxial growth are favorable for MgO substrates. As a result a substantial increase of tunneling magnetoresistance caused by spin-filtering effect was observed and reasonably theoretically explained. The value of TMR - 9.2% at room temperature in 18 kOe magnetic field is three times higher comparing to that for the samples grown on Corning glass substrates. PMID:23035505

  5. Secondary Al-Si-Mg High-pressure Die Casting Alloys with Enhanced Ductility

    NASA Astrophysics Data System (ADS)

    Bösch, Dominik; Pogatscher, Stefan; Hummel, Marc; Fragner, Werner; Uggowitzer, Peter J.; Göken, Mathias; Höppel, Heinz Werner

    2015-03-01

    Al-Si-Mg-based secondary cast alloys are attractive candidates for thin-walled high-pressure die castings for applications in the transport industry. The present study investigates the effect of manganese additions at high cooling rates on microstructure, mechanical properties, and on the dominating fracture mechanisms of alloy AlSi10Mg with an elevated iron concentration. Systematic variations of the Mn content from 0.20 to 0.85 wt pct at a constant Fe content of 0.55 wt pct illustrate the key changes in type, phase fraction, and shape of the Fe-containing intermetallic phases, and the corresponding influence on the alloy's ductility. For high-pressure die casting (HPDC), an optimal range of the Mn content between 0.40 and 0.60 wt pct, equivalent to a Mn/Fe ratio of approximately 1, has been identified. At these Mn and Fe contents, the high cooling rates obtained in HPDC result in the formation of fine and homogeneously distributed α-Al15(Fe,Mn)3Si2 phase, and crack initiation is transferred from AlFeSi intermetallics to eutectic silicon. The study interprets the microstructure-property relationship in the light of thermodynamic calculations which reveal a significant increase in undercooling of the α-Al15(Fe,Mn)3Si2 phase with increased Mn content. It concludes that the interdependence of the well-defined Mn/Fe ratio and the high cooling rate in HPDC can generate superior ductility in secondary AlSi10Mg cast alloys.

  6. Boron strengthening in FeAl

    SciTech Connect

    Baker, I.; Li, X.; Xiao, H.; Klein, O.; Nelson, C.; Carleton, R.L.; George, E.P.

    1998-11-01

    The effect of boron on the strength of B2-structured FeAl is considered as a function of composition, grain size and temperature. Boron does not affect the concentrations of antisite atoms or vacancies present, with the former increasing and the latter decreasing with increasing deviation from the stoichiometric composition. When vacancies are absent, the strength increase per at. % B per unit lattice strain, {Delta}{sigma}/({Delta}c x {epsilon}) increases with increasing aluminum concentration, but when vacancies are present (>45 at. % Al), {Delta}{sigma}/({Delta}c x {epsilon}) decreases again. Boron increases grain size strengthening in FeAl. B strengthening is roughly independent of temperature up to the yield strength peak but above the point, when diffusion-assisted deformation occurs, boron strengthening increases dramatically.

  7. Melting in the system CaO-MgO-Al2O3-SiO2-FeO-Cr2O3 spanning the plagioclase-spinel lherzolite transition at 7 to 10 kbar: experiments versus thermodynamics

    NASA Astrophysics Data System (ADS)

    Keshav, S.; Tirone, M.; Gudfinnsson, G.; Presnall, D.

    2008-12-01

    Voluminous basaltic magmas erupt at mid-oceanic ridges (mid-ocean ridge basalts, MORB) as a consequence of mantle upwelling and melting beneath spreading plates. However, because the geochemistry of MORB is distinct from OIB (ocean-island basalts), both have great petrogenetic significance and carry important information about the chemical and physical properties/dynamics of the mantle. In the context of MORB, a critical yet unresolved question is how phase transitions within a polybaric melting zone affect melt productivity and thereby, possibly exert control on major and trace element composition of erupted magmas. Currently, the disagreements on these issues are fundamental, with great consequences that extend beyond petrology to global issues of potential temperatures, mantle melting, mantle heterogeneity, and mantle dynamics. Thermodynamics show that melt productivity depends critically on the transition reaction, and melting can in principle increase, decrease, or even stop at a transition. Phase equilibrium work from both systems CaO-MgO-Al2O3-SiO2-Na2O (CMASN) and CMAS-FeO (CMASF) have been used to argue that melt productivity may increase at the plagioclase-spinel (pl-sp) transition because the univariant solidus transition reaction has a positive dT/dP slope in these systems, moving to higher pressure relative to the CMAS system. However, melting models derived on the basis of MELTS and pMELTS show that the solidus has a negative slope on the pl-sp transition. If correct, this would cause suppression of melting as the mantle decompresses along a pertinent adiabat. Owing to these vast discrepancies between experiments and thermodynamics and to further clarify MORB genesis, in this work we present melting phase relations in the system CMASFCr at the plagioclase-spinel lherzolite transition from 7 to 10 kbar. Cr was chosen since recent work has shown that the addition of Cr to CMAS has an unusually large effect on Ca/Al of melt compositions at 1.1 GPa. With

  8. The in vitro biocompatibility and macrophage phagocytosis of Mg17Al12 phase in Mg-Al-Zn alloys.

    PubMed

    Liu, Chen; He, Peng; Wan, Peng; Li, Mei; Wang, Kehong; Tan, Lili; Zhang, Yu; Yang, Ke

    2015-07-01

    Mg alloys are gaining interest for applications as biodegradable medical implant, including Mg-Al-Zn series alloys with good combination of mechanical properties and reasonable corrosion resistance. However, whether the existence of second phase particles in the alloys exerts influence on the biocompatibility is still not clear. A deeper understanding of how the particles regulate specific biological responses is becoming a crucial requirement for their subsequent biomedical application. In this work, the in vitro biocompatibility of Mg17Al12 as a common second phase in biodegradable Mg-Al-Zn alloys was investigated via hemolysis, cytotoxicity, cell proliferation, and cell adhesion tests. Moreover, osteogenic differentiation was evaluated by the extracellular matrix mineralization assay. The Mg17Al12 particles were also prepared to simulate the real situation of second phase in the in vivo environment in order to estimate the cellular response in macrophages to the Mg17Al12 particles. The experimental results indicated that no hemolysis was found and an excellent cytocompatibility was also proved for the Mg17Al12 second phase when co-cultured with L929 cells, MC3T3-E1 cells and BMSCs. Macrophage phagocytosis co-culture test revealed that Mg17Al12 particles exerted no harmful effect on RAW264.7 macrophages and could be phagocytized by the RAW264.7 cells. Furthermore, the possible inflammatory reaction and metabolic way for Mg17Al12 phase were also discussed in detail.

  9. Fabrication of Fe-Al nanoparticles by selective oxidation of Fe-Al thin films

    NASA Astrophysics Data System (ADS)

    Jang, Pyungwoo; Shin, Seungchan; Jung, Chip-Sup; Kim, Kwang-Ho; Seomoon, Kyu

    2013-04-01

    The possibility of a new technique for fabricating nanoparticles from thin films using selective oxidation in an atmosphere mixture of water vapor and hydrogen was investigated. Fe-5wt.%Al films were RF-sputtered and annealed in the atmosphere mixture at 900°C for up to 200 min, in order to oxidize aluminum selectively. Thermodynamics simulation showed that temperatures exceeding 800°C are necessary to prevent iron from being oxidized, as confirmed by the depth profile of XPS. As the annealing time increased, the morphology of the 200-nm Fe-Al films changed from the continuous to the discontinuous type; thus, particulate Fe-Al films formed after 100 min. The particulate 10- to 100-nm Fe-Al films showed super-paramagnetic behavior after the oxidation. Thus, a new technique for fabricating nanoparticles was successfully introduced using selective oxidation.

  10. Effect of MgO spacer and annealing on interface and magnetic properties of ion beam sputtered NiFe/Mg/MgO/CoFe layer structures

    SciTech Connect

    Bhusan Singh, Braj; Chaudhary, Sujeet

    2012-09-15

    The effect of variation in the thickness of ion assisted ion beam sputtered MgO spacer layer deposited at oxygen ion assisted energy of 50 eV on the extent of magnetic coupling of NiFe and CoFe layers in Si/NiFe(10 nm)/Mg(1 nm)/MgO(2,4,6 nm)/CoFe(10 nm) sandwich structure is investigated. At MgO spacer layer thickness of 4 nm, the separate reversal of magnetizations of the two ferromagnetic layers is observed in the hystresis loop recorded along easy direction. This results in a 3.5 Oe wide plateau like region during magnetization reversal, which became 4.5 Oe at 6 nm thin MgO. At 2 nm thin MgO, the absence of plateau during magnetization reversal region revealed ferromagnetic coupling between the two ferromagnetic layers, which is understood to arise due to the growth of very thin and low density (1.22 gm/cc) MgO spacer layer, indicating the presence of pinholes as revealed by x-ray reflectometry. After vaccum annealing (200 Degree-Sign C/1 h), the plateau region for 4 and 6 nm thin MgO case decreased to 1.5 Oe and 2.0 Oe, respectively, due to enhanced interface roughness/mixing. In addition, an enhancement of the in-plane magnetic anisotropy is also observed.

  11. Room temperature luminescence and ferromagnetism of AlN:Fe

    NASA Astrophysics Data System (ADS)

    Li, H.; Cai, G. M.; Wang, W. J.

    2016-06-01

    AlN:Fe polycrystalline powders were synthesized by a modified solid state reaction (MSSR) method. Powder X-ray diffraction and transmission electron microscopy results reveal the single phase nature of the doped samples. In the doped AlN samples, Fe is in Fe2+ state. Room temperature ferromagnetic behavior is observed in AlN:Fe samples. Two photoluminescence peaks located at about 592 nm (2.09 eV) and 598 nm (2.07 eV) are observed in AlN:Fe samples. Our results suggest that AlN:Fe is a potential material for applications in spintronics and high power laser devices.

  12. Forging of FeAl intermetallic compounds

    SciTech Connect

    Flores, O.; Juarez, J.; Campillo, B.; Martinez, L.; Schneibel, J.H.

    1994-09-01

    Much activity has been concentrated on the development of intermetallic compounds with the aim of improving tensile ductility, fracture toughness and high notch sensitivity in order to develop an attractive combination of properties for high and low temperature applications. This paper reports experience in processing and forging of FeAl intermetallic of B2 type. During the experiments two different temperatures were employed, and the specimens were forged after annealing in air, 10{sup {minus}2} torr vacuum and argon. From the results it was learned that annealing FeAl in argon atmosphere prior to forging resulted in better deformation behavior than for the other two environments. For the higher forging temperature used in the experiments (700C), the as-cast microstructure becomes partially recrystallized.

  13. Positron lifetime studies of decomposition in 2024 (Al-Cu-Mg) and 7010 (Al-Zn-Cu-Mg) alloys

    SciTech Connect

    Dlubek, G. |; Lademann, P.; Krause, H.; Krause, S.; Unger, R.

    1998-09-04

    In the current paper, the decomposition behavior of the engineering alloys 2024 (Al-Cu-Mg) and 7010 (Al-Zn-Cu-Mg) is studied using positron lifetime measurements. Positrons probe open volume defects such as vacancies and dislocations. However, they may also be used to investigate coherent zones and incoherent precipitates. In order to understand the rather complicated precipitation sequences and the response of positrons to different type of precipitates occurring in 2024 and 7010 alloys, binary and ternary laboratory alloys were also investigated under the same experimental conditions as the engineering alloys. The interpretations of the results are based on experiences of the group from extensive positron studies of laboratory alloys such as Al-Zn, Al-Zn-Mg, Al-Cu, and further Al alloys (see also the review (4)). Their collected results are shown as lifetimes and curve-shape parameters S of the electron-positron momentum distribution curves characteristic for different precipitates in Al alloys.

  14. Room-temperature perpendicular magnetic anisotropy of MgO/Fe/MgO ultrathin films

    SciTech Connect

    Kozioł-Rachwał, A.; Ślęzak, T.; Przewoźnik, J.; Skowroński, W.; Stobiecki, T.; Wilgocka-Ślęzak, D.; Qin, Q. H.; Dijken, S. van; Korecki, J.

    2013-12-14

    We used the anomalous Hall effect to study the magnetic properties of MgO/Fe(t)/MgO(001) structures in which the Fe thickness t ranged from 4 Å to 14 Å. For the iron deposited at 140 K, we obtained perpendicular magnetization at room temperature below the critical thickness of t{sub c} = (9 ± 1) Å. In the vicinity of t{sub c}, the easy magnetization axis switched from an out-of-plane orientation to an in-plane orientation, and the observed spin-reorientation transition was considered in terms of the competition among different anisotropies. The perpendicular magnetization direction was attributed to magnetoelastic anisotropy. Finally, the temperature-dependent spin-reorientation transition was analyzed for Fe thicknesses close to t{sub c}.

  15. The effect of the MgO buffer layer thickness on magnetic anisotropy in MgO/Fe/Cr/MgO buffer/MgO(001)

    NASA Astrophysics Data System (ADS)

    Kozioł-Rachwał, Anna; Nozaki, Takayuki; Zayets, Vadym; Kubota, Hitoshi; Fukushima, Akio; Yuasa, Shinji; Suzuki, Yoshishige

    2016-08-01

    The relationship between the magnetic properties and MgO buffer layer thickness d was studied in epitaxial MgO/Fe(t)/Cr/MgO(d) layers grown on MgO(001) substrate in which the Fe thickness t ranged from 0.4 nm to 1.1 nm. For 0.4 nm ≤ t ≤ 0.7 nm, a non-monotonic coercivity dependence on the MgO buffer thickness was shown by perpendicular magneto-optic Kerr effect magnetometry. For thicker Fe films, an increase in the buffer layer thickness resulted in a spin reorientation transition from perpendicular to the in-plane magnetization direction. Possible origins of these unusual behaviors were discussed in terms of the suppression of carbon contamination at the Fe surface and changes in the magnetoelastic anisotropy in the system. These results illustrate a method to control magnetic anisotropy in MgO/Fe/Cr/MgO(d) via an appropriate choice of MgO buffer layer thickness d.

  16. Tunneling conductance studies in the ion-beam sputtered CoFe/Mg/MgO/NiFe magnetic tunnel junctions

    SciTech Connect

    Singh, Braj Bhusan; Chaudhary, Sujeet

    2013-06-03

    Magnetic tunnel junctions consisting of CoFe(10 nm)/Mg(1 nm)/MgO(3.5 nm)/NiFe(10 nm) are grown at room temperature using dual ion beam sputtering via in-situ shadow masking. The effective barrier thickness and average barrier height are estimated to be 3.5 nm (2.9 nm) and 0.69 eV (1.09 eV) at 290 K (70 K), respectively. The tunnel magnetoresistance value of 0.2 % and 2.3 % was observed at 290 K and 60 K, respectively. The temperature dependence of tunneling conductance revealed the presence of localized states present within the forbidden gap of the MgO barrier leading to finite inelastic spin independent tunneling contributions, which degrade the TMR value.

  17. A comparison of mechanical properties between Al and Al3Mg

    NASA Astrophysics Data System (ADS)

    Yang, Rong; Tang, Bin; Gao, Tao

    2016-11-01

    On the basis of first principles calculations, we have calculated the elastic properties, stress-strain relations, ideal tensile strengths, ideal shear strengths, and the ideal compressed strengths of Al and Al3Mg. The stress-strain relations of Al3Mg are strikingly similar to those of Al, indicating that the crystal structure appears to be more important than the identity of the individual atoms during uniaxial deformation. Al3Mg is found to have larger moduli and higher strengths than Al but less ductile than Al. So Al3Mg is expected to be a harder material, consistent with its exploitation in Al precipitate-hardening mechanisms. The calculated elastic properties, tensile strengths and shear strengths of Al are consistent with experimental values or previous theoretical results. We also use another method (molecular dynamics (MD) simulations) to recalculate elastic constants, ideal tensile and compressed strength of Al3Mg for checking and comparing. We find that the results obtained by the two methods agree well with each other. The failure modes under uniaxial <100> tension are also explored for Al and Al3Mg. Our calculations confirm that Al fail by shear and predict that Al3Mg also fail by shear.

  18. Laser-Ultrasonic Inspection of MG/AL Castings

    SciTech Connect

    Blouin, Alain; Levesque, Daniel; Monchalin, Jean-Pierre; Baril, Eric; Fischersworring-Bunk, Andreas

    2005-04-09

    Laser-ultrasonics is used to assess the metallurgical bond between Mg/Al materials in die-cast Magnesium/Aluminum composite. The acoustic impedances of Mg, Al and air are such that the amplitude of ultrasonic echoes reflected back from a void is many times larger than the amplitude of those reflected back from a well-bonded interface. In addition, the polarity of echoes from a void is inverted compared to that from a well-bonded interface. Laser-ultrasonic F-SAFT is also used for imaging tilted Mg/Al interfaces. Experimental setup, signal processing and results for detecting voids in the Mg/Al interface of cast parts are presented.

  19. Dissolution of Cu/Mg Bearing Intermetallics in Al-Si Foundry Alloys

    NASA Astrophysics Data System (ADS)

    Javidani, Mousa; Larouche, Daniel; Grant Chen, X.

    2016-08-01

    Evolutions of the Cu/Mg bearing intermetallics were thoroughly investigated in four Al-Si hypoeutectic alloys containing various Cu (1 and 1.6 wt pct) and Mg (0.4 and 0.8 wt pct) contents. The area fractions of Cu/Mg bearing phases before and after solution heat treatment (SHT) were quantified to evaluate the solubility/stability of the phases. Two Mg-bearing intermetallics (Q-Al5Cu2Mg8Si6, π-Al8FeMg3Si6) which appear as gray color under optical microscope were discriminated by the developed etchant. Moreover, the concentrations of the elements (Cu, Mg, and Si) in α-Al were analyzed. The results illustrated that in the alloys containing ~0.4 pct Mg, Q-Al5Cu2Mg8Si6 phase was dissolved after 6 hours of SHT at 778 K (505 °C); but containing in the alloys ~0.8 pct Mg, it was insoluble/ partially soluble. Furthermore, after SHT at 778 K (505 °C), Mg2Si was partially substituted by Q-phase. Applying a two-step SHT [6 hours@778 K (505 °C) + 8 hours@798 K (525 °C)] in the alloys containing ~0.4 pct Mg helped to further dissolve the remaining Mg bearing intermetallics and further modified the microstructure, but in the alloys containing ~0.8 pct Mg, it caused partial melting of Q-phase. Thermodynamic calculations were carried out to assess the phase formation in equilibrium and in non-equilibrium conditions. There was an excellent agreement between the experimental results and the predicted results.

  20. Dissolution of Cu/Mg Bearing Intermetallics in Al-Si Foundry Alloys

    NASA Astrophysics Data System (ADS)

    Javidani, Mousa; Larouche, Daniel; Grant Chen, X.

    2016-10-01

    Evolutions of the Cu/Mg bearing intermetallics were thoroughly investigated in four Al-Si hypoeutectic alloys containing various Cu (1 and 1.6 wt pct) and Mg (0.4 and 0.8 wt pct) contents. The area fractions of Cu/Mg bearing phases before and after solution heat treatment (SHT) were quantified to evaluate the solubility/stability of the phases. Two Mg-bearing intermetallics (Q-Al5Cu2Mg8Si6, π-Al8FeMg3Si6) which appear as gray color under optical microscope were discriminated by the developed etchant. Moreover, the concentrations of the elements (Cu, Mg, and Si) in α-Al were analyzed. The results illustrated that in the alloys containing ~0.4 pct Mg, Q-Al5Cu2Mg8Si6 phase was dissolved after 6 hours of SHT at 778 K (505 °C); but containing in the alloys ~0.8 pct Mg, it was insoluble/ partially soluble. Furthermore, after SHT at 778 K (505 °C), Mg2Si was partially substituted by Q-phase. Applying a two-step SHT [6 hours@778 K (505 °C) + 8 hours@798 K (525 °C)] in the alloys containing ~0.4 pct Mg helped to further dissolve the remaining Mg bearing intermetallics and further modified the microstructure, but in the alloys containing ~0.8 pct Mg, it caused partial melting of Q-phase. Thermodynamic calculations were carried out to assess the phase formation in equilibrium and in non-equilibrium conditions. There was an excellent agreement between the experimental results and the predicted results.

  1. Temperature dependence of resistance in epitaxial Fe/MgO/Fe magnetic tunnel junctions

    SciTech Connect

    Ma, Q. L.; Wang, Shouguo; Wang, Y.; Zhang, J.; Ward, R. C. C.; Kohn, A.; Zhang, Xiaoguang; Han, Prof. X. F.

    2009-01-01

    The temperature dependence of resistance in parallel P and antiparallel AP configurations RP,AP has been investigated in epitaxial Fe/MgO/Fe junctions with varying MgO barrier thicknesses tMgO. RAP exhibits a substantial decrease with increasing temperature for samples with tMgO ranging from 3.0 to 1.5 nm. In contrast, RP is approximately temperature independent when tMgO =3.0 nm and increases with temperature when tMgO=2.1 and 1.5 nm. Possible origins of this temperature dependence of resistance, which include taking into account a spin independent term and consideration of spin-flip scattering, are discussed. We attribute the temperature dependence of RP,AP to the misalignment of magnetic moments in the electrodes due to thermal excitations and its effect on the spin dependent tunneling.

  2. Spontaneously intermixed Al-Mg barriers enable corrosion-resistant Mg/SiC multilayer coatings

    SciTech Connect

    Soufli, Regina; Fernandez-Perea, Monica; Baker, Sherry L.; Robinson, Jeff C.; Alameda, Jennifer; Walton, Christopher C.

    2012-07-24

    Magnesium/silicon carbide (Mg/SiC) has the potential to be the best-performing reflective multilayercoating in the 25–80 nm wavelength region but suffers from Mg-related corrosion, an insidious problem which completely degrades reflectance. We have elucidated the origins and mechanisms of corrosion propagation within Mg/SiC multilayers. Based on our findings, we have demonstrated an efficient and simple-to-implement corrosion barrier for Mg/SiC multilayers. In conclusion, the barrier consists of nanometer-scale Mg and Al layers that intermix spontaneously to form a partially amorphous Al-Mg layer and is shown to prevent atmospheric corrosion while maintaining the unique combination of favorable Mg/SiC reflective properties.

  3. Interfacial electronic transport phenomena in single crystalline Fe-MgO-Fe thin barrier junctions

    SciTech Connect

    Gangineni, R. B.; Negulescu, B.; Baraduc, C.; Gaudin, G.

    2014-05-05

    Spin filtering effects in nano-pillars of Fe-MgO-Fe single crystalline magnetic tunnel junctions are explored with two different sample architectures and thin MgO barriers (thickness: 3–8 monolayers). The two architectures, with different growth and annealing conditions of the bottom electrode, allow tuning the quality of the bottom Fe/MgO interface. As a result, an interfacial resonance states (IRS) is observed or not depending on this interface quality. The IRS contribution, observed by spin polarized tunnel spectroscopy, is analyzed as a function of the MgO barrier thickness. Our experimental findings agree with theoretical predictions concerning the symmetry of the low energy (0.2 eV) interfacial resonance states: a mixture of Δ{sub 1}-like and Δ{sub 5}-like symmetries.

  4. Unusually large spin polarization and magnetoresistance in a FeMg8-FeMg8 superatomic dimer.

    PubMed

    Zhu, Lin; Qian, Meichun; Khanna, Shiv N

    2013-08-14

    Electronic transport across a FeMg8 magnetic superatom and its dimer has been investigated using a density functional theory combined with Keldysh nonequilibrium Green's-function formalism. For a single cluster, our studies for the cluster supported in various orientations on a Au(100) surface show that the transport is sensitive to the contact geometry. Investigations covering the cases where the axes of Mg square antiprism are 45°, perpendicular, and parallel to the transport direction, show that the equilibrium conductance, transferred charge, and current polarizations can all change significantly with orientation. Our studies on the transport across a magnetic superatom dimer FeMg8-FeMg8 focus on the effect of electrode contact distance and the support. The calculated I-V curves show negative differential resistance behavior at larger electrode-cluster contact distances. Further, the equilibrium conductance in ferromagnetic state shows an unusually high spin polarization that is about 81.48% for specific contact distance, and a large magnetoresistance ratio exceeding 500% is also found. The results show that the superatom assemblies can provide unusual transport characteristics, and that the spin polarization and magnetoresistance can be controlled via the contact geometry.

  5. Melting of (Mg, Fe)O Ferropericlase at High Pressure (> 40 GPa)

    NASA Astrophysics Data System (ADS)

    Deng, J.; Du, Z.; Lee, K. K. M.

    2015-12-01

    (Mg, Fe)O ferropericlase is the second most abundant mineral in Earth's lower mantle. Previous laser-heated diamond-anvil cell (LHDAC) experiments on ferropericlase yielded an MgO melting curve consistent with ab initio predictions and suggested that FeO forms a complete solid solution with MgO at least up to ~40 GPa [Du and Lee, 2014]. But the melting behavior of ferropericlase at pressures greater than 40 GPa remains poorly constrained. We have performed LHDAC experiments using in situ two-dimensional multi-wavelength imaging radiometry and ex situ chemical and textural analyses of samples melted at ~70 GPa. Our results suggest that ferropericlase deviates from an ideal solid solution to possibly eutectic behavior, assuming the MgO melting curve is still predicted well by ab initio computational methods. Additionally, we find an offset between the centers of the two-dimensional maps of emissivity and temperature. A tentative interpretation is that the (Mg, Fe)O becomes metallic at high pressures and temperatures [Ohta et al., 2014; Ovchinnikov, 2011; Ovchinnikov et al., 2012] and thus the intensity of light absorbed by the solid surrounding the molten region is strongly wavelength dependent, leading to the uneven variation in light intensity detected by the multi-wavelength imaging radiometric temperature measurement system and consequently abnormal correlation between temperature and emissivity.

  6. Electrical transport in amorphous semiconducting AlMgB14 films

    NASA Astrophysics Data System (ADS)

    Tian, Y.; Li, G.; Shinar, J.; Wang, N. L.; Cook, B. A.; Anderegg, J. W.; Constant, A. P.; Russell, A. M.; Snyder, J. E.

    2004-08-01

    The electrical transport properties of semiconducting AlMgB14 films deposited at room temperature and 573K are reported in this letter. The as-deposited films are amorphous, and they exhibit high n-type electrical conductivity, which is believed to stem from the conduction electrons donated by Al, Mg, and/or Fe impurities in these films. The film deposited at 573K is less conductive than the room-temperature-deposited film. This is attributed to the nature of donor or trap states in the band gap related to the different deposition temperatures.

  7. Preliminary study of the characteristics of a high Mg containing Al-Mg-Si alloy

    NASA Astrophysics Data System (ADS)

    Yan, F.; McKay, B. J.; Fan, Z.; Chen, M. F.

    2012-01-01

    An Al-20Mg-4Si high Mg containing alloy has been produced and its characteristics investigated. The as-cast alloy revealed primary Mg2Si particles evenly distributed throughout an α-Al matrix with a β-Al3Mg2 fully divorced eutectic phase observed in interdendritic regions. The Mg2Si particles displayed octahedral, truncated octahedral, and hopper morphologies. Additions of Sb, Ti and Zr had a refining influence reducing the size of the Mg2Si from 52 ± 4 μm to 25 ± 0.1 μm, 35 ± 1 μm and 34 ± 1 μm respectively. HPDC tensile test samples could be produced with a 0.6 wt.% Mn addition which prevented die soldering. Solution heating for 1 hr was found to dissolve the majority of the Al3Mg2 eutectic phase with no evidence of any effect on the primary Mg2Si. Preliminary results indicate that the heat treatment has a beneficial effect on the elongation and the UTS.

  8. Effect of interfacial structures on spin dependent tunneling in epitaxial L1{sub 0}-FePt/MgO/FePt perpendicular magnetic tunnel junctions

    SciTech Connect

    Yang, G.; Li, D. L.; Wang, S. G. Ma, Q. L.; Liang, S. H.; Wei, H. X.; Han, X. F.; Hesjedal, T.; Ward, R. C. C.; Kohn, A.; Elkayam, A.; Tal, N.; Zhang, X.-G.

    2015-02-28

    Epitaxial FePt(001)/MgO/FePt magnetic tunnel junctions with L1{sub 0}-FePt electrodes showing perpendicular magnetic anisotropy were fabricated by molecular beam epitaxial growth. Tunnel magnetoresistance ratios of 21% and 53% were obtained at 300 K and 10 K, respectively. Our previous work, based on transmission electron microscopy, confirmed a semi-coherent interfacial structure with atomic steps (Kohn et al., APL 102, 062403 (2013)). Here, we show by x-ray photoemission spectroscopy and first-principles calculation that the bottom FePt/MgO interface is either Pt-terminated for regular growth or when an Fe layer is inserted at the interface, it is chemically bonded to O. Both these structures have a dominant role in spin dependent tunneling across the MgO barrier resulting in a decrease of the tunneling magnetoresistance ratio compared with previous predictions.

  9. Microstructure Evolution and Mechanical Properties of Al/Al-Mg/Al composite sheet metals

    NASA Astrophysics Data System (ADS)

    Cho, Jaehyung; Kim, Su-Hyeon; Kim, Hyoung-Wook; Lim, Cha-Yong; Kim, Eun-Young; Choi, Shi-Hoon

    2011-08-01

    Two different types of aluminum alloys of AA1050 and AA5182 were used to manufacture Al/Al-Mg/Al composite sheet metals by roll bonding technology at room temperature. The composite sheet metals were annealed at 400 °C and carried out uniaxial tension tests to investigate mechanical properties. Macroscopic mechanical properties are strongly dependent on the volume (or thickness) fraction of two component layers. Microstructure and texture evolution were also investigated during roll bonding process. The AA1050 sheets located in the outer layer mainly consist of shear texture components and the AA5182 sheet located in the center layer consists of plane strain texture components. With differential speeds of the top and bottom rolls, roll bonding was also carried out. Elongation along the RD and TD was improved at a speed difference of approximately 10%-20%.

  10. Multistage growth of Fe-Mg-carpholite and Fe-Mg-chloritoid, from field evidence to thermodynamic modelling

    NASA Astrophysics Data System (ADS)

    Pourteau, Amaury; Bousquet, Romain; Vidal, Olivier; Plunder, Alexis; Duesterhoeft, Erik; Candan, Osman; Oberhänsli, Roland

    2015-04-01

    We provide new insights into the prograde evolution of HP/LT meta-sedimentary rocks on the basis of detailed petrologic examination, element-partitioning analysis, and thermodynamic modelling of well-preserved Fe-Mg-carpholite- and chloritoid-bearing rocks from the Afyon zone (Anatolia). Study samples, stemming from three different areas of the metamorphic belt, include typical quartz-carpholite veins as well as quartz-free and quartz-bearing phyllites. All samples exhibit multiple stages of carpholite, whereas zoning was until now rarely documented in this type of rocks. We document continuous, and discontinuous compositional (ferro-magnesian substitution) zoning of carpholite (overall XMg = 0.27-0.73) and chloritoid (overall XMg = 0.07-0.30), as well as clear equilibrium, and disequilibrium (i.e. reaction-related) textures involving carpholite and chloritoid, which consistently account for the consistent enrichment in Mg of both minerals through time, and the progressive replacement of carpholite by chloritoid. Mg/Fe distribution coefficients calculated between carpholite and chloritoid vary widely within samples (2.2-20.0). Among this range, only values of 7-11 correlate with equilibrium textures, in agreement with data from the literature. Equilibrium phase diagrams for (NaK)FMASH rock compositions are calculated using a newly modified thermodynamic dataset, including most recent data for carpholite, chloritoid, chlorite, and white mica, as well as further refinements for Fe-carpholite, and both chloritoid end-members, as required to reproduce accurately petrologic observations (phase relations, experimental constraints, Mg/Fe partitioning). Modelling reveals that Mg/Fe partitioning between carpholite and chloritoid is greatly sensitive to temperature, and calls for a future evaluation of possible use as a thermometer, valid for blueschist-facies conditions, which has so far been missing. In addition, calculations show significant effective bulk composition

  11. Strength of (Mg,Fe)O Ferropericlase in Earth's Lower Mantle

    NASA Astrophysics Data System (ADS)

    Marquardt, H.; Miyagi, L. M.

    2013-12-01

    Ferropericlase (Mg,Fe)O is thought to be the second most abundant mineral phase in Earth's lower mantle. Due to its potentially weak rheological behavior it may play a key role in controlling rheology of the lower mantle and in generating seismic anisotropy (e.g. McNamara et al. 2002; Marquardt et al. 2009). At a pressure range of approximately 40 to 70 GPa at 300 K, the ferrous iron in ferropericlase undergoes a spin crossover from high-spin to low-spin state (Badro et al. 2003). Our understanding of the impact of the spin crossover on ferropericlase strength is incomplete. The only published deformation study on (Mg,Fe)O through the spin transition (Lin et al. 2009) pressure region has very limited pressure resolution. However, the results of the previous study indicate a decrease of ferropericlase strength throughout the spin crossover region and in the low-spin state. Here, we present new results from synchrotron radial x-ray diffraction measurements on (Mg0.9Fe0.1)O and (Mg0.8Fe0.2)O carried out at the Advanced Light Source (Lawrence Berkeley National Laboratory) throughout the entire spin crossover pressure range up to 100 GPa. In our experiments, pressure was remotely increased using a gas membrane system, which allows for obtaining a very fine pressure resolution. In contrast to the previous report of Lin et al., our data do not show any decrease of average differential strains (and thus strength) in ferropericlase across the spin crossover. In contrast, our experiments suggest that the strength of ferropericlase increases when iron changes from high to low-spin state and remains high in low-spin state. We will discuss our findings in light of their implications for lower mantle dynamics. Badro, J., et al. (2003). Science 300(5620): 789-791. Lin, J.-F., et al. (2009). Physics and Chemistry of Minerals 36(10): 585-592. Marquardt, H., et al. (2009). Science 324(5924): 224-226. McNamara, A. K., et al. (2002). Nature 416(6878): 310-314.

  12. Interfacial Characterization of Dissimilar Joints Between Al/Mg/Al-Trilayered Clad Sheet to High-Strength Low-Alloy Steel

    NASA Astrophysics Data System (ADS)

    Macwan, A.; Jiang, X. Q.; Chen, D. L.

    2015-07-01

    Magnesium (Mg) alloys are increasingly used in the automotive and aerospace sectors to reduce vehicle weight. Al/Mg/Al tri-layered clad sheets are deemed as a promising alternative to improve the corrosion resistance and formability of Mg alloys. The structural application of Al/Mg/Al tri-layered clad sheets inevitably involves welding and joining in the multi-material vehicle body manufacturing. This study aimed to characterize the bonding interface microstructure of the Al/Mg/Al-clad sheet to high-strength low-alloy steel with and without Zn coating using ultrasonic spot welding at different levels of welding energy. It was observed that the presence of Zn coating improved the bonding at the interface due to the formation of Al-Zn eutectic structure via enhanced diffusion. At a higher level of welding energy, characteristic flow patterns of Zn into Al-clad layer were observed with an extensive penetration mainly along some high angle grain boundaries. The dissimilar joints without Zn coating made at a high welding energy of 800 J failed partially from the Al/Fe weld interface and partially from the Al/Mg clad interface, while the joints with Zn coating failed from the Al/Mg clad interface due to the presence of brittle Al12Mg17 phase.

  13. Effect of sonotrode material on grain refining of Mg-3Al and Mg-9Al alloys by ultrasonic melt treatment

    NASA Astrophysics Data System (ADS)

    Youn, Jeong IL; Lee, Young Ki; Jig Kim, Young; Park, Jeong Wook

    2016-07-01

    The new process, nucleation enhanced ultrasonic melt treatment (NEUMT), was proposed to increase the refining efficiency through heterogeneous nucleation by using the sonotrode which has been only concerned with the medium to transfer the ultrasonic energy. In the processing, the metal atoms and/or clusters eroded from the sonotrode were supplied and were simultaneously mixed uniformly into the melt by the ultrasound. These particles act as potential nuclei and refine the structure. The process was applied to assess grain refinement of Mg alloys, especially Mg-3Al and Mg-9Al. The refining efficiency was affected by the sonotrode material, and Ti was very effective in this process by the formation of proper intermetallic compound in the Mg alloy melt. The intermetallic compound was searched by the calculation of plane disregistry of the crystallographic orientation, and Al3Ti was suggested to be the heterogeneous nuclei.

  14. Overview of the development of FeAl intermetallic alloys

    SciTech Connect

    Maziasz, P.J.; Liu, C.T.; Goodwin, G.M.

    1995-09-01

    B2-phase FeAl ordered intermetallic alloys based on an Fe-36 at.% Al composition are being developed to optimize a combination of properties that includes high-temperature strength, room-temperature ductility, and weldability. Microalloying with boron and proper processing are very important for FeAl properties optimization. These alloys also have the good to outstanding resistance to oxidation, sulfidation, and corrosion in molten salts or chlorides at elevated temperatures, characteristic of FeAl with 30--40 at.% Al. Ingot- and powder-metallurgy (IM and PM, respectively) processing both produce good properties, including strength above 400 MPa up to about 750 C. Technology development to produce FeAl components for industry testing is in progress. In parallel, weld-overlay cladding and powder coating technologies are also being developed to take immediate advantage of the high-temperature corrosion/oxidation and erosion/wear resistance of FeAl.

  15. Hydrothermal synthesis of Mg-Al hydrotalcites by urea hydrolysis

    SciTech Connect

    Rao, M. Mohan . E-mail: mandapati@iict.res.in; Reddy, B. Ramachandra; Jayalakshmi, M.; Jaya, V. Swarna; Sridhar, B.

    2005-02-15

    We report a simple method to prepare hydrotalcites involving both urea hydrolysis and hydrothermal synthetic conditions. Out of a series of Mg/Al ratios tried, pure hydrotalcite like phase was obtained for Mg/Al ratios of 1:1 and 2:1. Unlike in conventional co-precipitation method we succeeded in preparing Mg/Al ratio of 1:1 by this route. The high temperature (180 deg. C) applied and pressure developed in the autoclave during the synthesis might have altered the topochemical transformation. The materials were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared, thermo gravimetric and differential thermal analysis and transmission electron microscopy.

  16. The Interplay of Al and Mg Speciation in Advanced Mg Battery Electrolyte Solutions.

    PubMed

    See, Kimberly A; Chapman, Karena W; Zhu, Lingyang; Wiaderek, Kamila M; Borkiewicz, Olaf J; Barile, Christopher J; Chupas, Peter J; Gewirth, Andrew A

    2016-01-13

    Mg batteries are an attractive alternative to Li-based energy storage due to the possibility of higher volumetric capacities with the added advantage of using sustainable materials. A promising emerging electrolyte for Mg batteries is the magnesium aluminum chloride complex (MACC) which shows high Mg electrodeposition and stripping efficiencies and relatively high anodic stabilities. As prepared, MACC is inactive with respect to Mg deposition; however, efficient Mg electrodeposition can be achieved following an electrolytic conditioning process. Through the use of Raman spectroscopy, surface enhanced Raman spectroscopy, (27)Al and (35)Cl nuclear magnetic resonance spectroscopy, and pair distribution function analysis, we explore the active vs inactive complexes in the MACC electrolyte and demonstrate the codependence of Al and Mg speciation. These techniques report on significant changes occurring in the bulk speciation of the conditioned electrolyte relative to the as-prepared solution. Analysis shows that the active Mg complex in conditioned MACC is very likely the [Mg2(μ-Cl)3·6THF](+) complex that is observed in the solid state structure. Additionally, conditioning creates free Cl(-) in the electrolyte solution, and we suggest the free Cl(-) adsorbs at the electrode surface to enhance Mg electrodeposition.

  17. Energetic ion bombarded Fe/Al multilayers

    SciTech Connect

    Al-Busaidy, M.S.; Crapper, M.D.

    2006-05-15

    The utility of ion-assisted deposition is investigated to explore the possibility of counteracting the deficiency of back-reflected current of Ar neutrals in the case of lighter elements such as Al. A range of energetically ion bombarded Fe/Al multilayers sputtered with applied surface bias of 0, -200, or -400 V were deposited onto Si(111) substrates in an argon atmosphere of 4 mTorr using a computer controlled dc magnetron sputtering system. Grazing incidence reflectivity and rocking curve scans by synchrotron x rays of wavelength of 1.38 A were used to investigate the structures of the interfaces produced. Substantial evidence has been gathered to suggest the gradual suppression of interfacial mixing and reduction in interfacial roughness with increases of applied bias. The densification of the Al microstructure was noticeable and may be a consequence of resputtering attributable to the induced ion bombardment. The average interfacial roughnesses were calculated for the 0, -200, and -400 V samples to be 7{+-}0.5, 6{+-}0.5, and 5{+-}0.5 A respectfully demonstrating a 30% improvement in interface quality. Data from rocking curve scans point to improved long-range correlated roughness in energetically deposited samples. The computational code based on the recursive algorithm developed by Parratt [Phys. Rev. 95, 359 (1954)] was successful in the simulation of the specular reflectivity curves.

  18. Model for nonprotective oxidation of Al-Mg alloys

    SciTech Connect

    Zayan, M.H. )

    1990-12-01

    The oxidation of Al-5Mg alloy has been studied at 550 C in dry air. Morphological details of the MgO layers which develop on this alloy during high-temperature oxidation have been studied by scanning electron microscopy (SEM). A localized detachment of the protective, adherent MgO layer was found, which is caused by voids formed by vacancy condensation at the metal-oxide interface. The source of these vacancies was the outward diffusion of Mg though the oxide layer. Continuing growth of these voids was responsible for cracking of oxide ridges and nodules, as well as the growth of new MgO having a cauliflower morphology. A model describing the process of the outward diffusion is given.

  19. Synthesis and properties of A{sub 6}B{sub 2}(OH){sub 16}Cl{sub 2}.4H{sub 2}O (A = Mg, Ni, Zn, Co, Mn and B = Al, Fe) materials for environmental applications

    SciTech Connect

    Dias, Anderson; Cunha, Lumena; Vieira, Andiara C.

    2011-09-15

    Highlights: {yields} A{sub 6}B{sub 2}(OH){sub 16}Cl{sub 2}.4H{sub 2}O (A = Mg, Ni, Zn, Co, Mn and B = Al, Fe) materials were synthesized. {yields} Chemical synthesis produced different levels of crystallinity and ordering degree. {yields} Structural investigation by Raman scattering revealed a complex band structure. {yields} A strong correlation between band structure and ionic radius was determined. -- Abstract: Double layered hydroxide materials of composition A{sub 6}B{sub 2}(OH){sub 16}Cl{sub 2}.4H{sub 2}O (A = Mg, Ni, Zn, Co, Mn and B = Al, Fe) were synthesized by chemical precipitation at 60 {sup o}C. Different levels of crystallinity and ordering degree were observed depending upon the chemical environment or the combination between divalent and trivalent cations. The results from high-resolution transmission electron microscopy revealed that nanostructured layered samples were obtained with interplanar spacing compatible with previous literature. Raman scattering was employed to investigate the complex band structure observed, particularly the lattice vibrations at lower frequencies, which is intimately correlated to the cationic radius of both divalent and trivalent ions. The results showed that strongly coordinated water and chloride ions besides highly structured hydroxide layers have a direct influence on the stability of the hydrotalcites. It was observed that transition and decomposition temperatures varied largely for different chemical compositions.

  20. Large anisotropic Fe orbital moments in perpendicularly magnetized Co2FeAl Heusler alloy thin films revealed by angular-dependent x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Okabayashi, Jun; Sukegawa, Hiroaki; Wen, Zhenchao; Inomata, Koichiro; Mitani, Seiji

    2013-09-01

    Perpendicular magnetic anisotropy (PMA) in Heusler alloy Co2FeAl thin films sharing an interface with a MgO layer is investigated by angular-dependent x-ray magnetic circular dichroism. Orbital and spin magnetic moments are deduced separately for Fe and Co 3d electrons. In addition, the PMA energies are estimated using the orbital magnetic moments parallel and perpendicular to the film surfaces. We found that PMA in Co2FeAl is determined mainly by the contribution of Fe atoms with large orbital magnetic moments, which are enhanced at the interface between Co2FeAl and MgO. Furthermore, element specific magnetization curves of Fe and Co are found to be similar, suggesting the existence of ferromagnetic coupling between Fe and Co PMA directions.

  1. Elasticity of AlFeO3 and FeAlO3 perovskite and post-perovskite from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Caracas, R.

    2010-10-01

    We use state-of-the-art ab initio calculations based on the generalized gradient approximation of the density functional theory in the planar augmented wavefunction formalism to determine the elastic constants tensor of perovskite and post-perovskite with formulas AlFeO3 and FeAlO3 in which Fe or Al respectively occupy only octahedral sites, for the stable magnetic configurations. The phase transition between perovskite and post-perovskite is associated with a site exchange, during which Fe from the inter-octahedral site in perovskite moves into the octahedral site in post-perovskite. Following this transition path the elastic moduli show positive jumps, considerably larger than for MgSiO3. The phase transition is marked by a positive jump of 0.04 km/s (0.33%) in the velocity of the compressional waves and by a negative jump of -0.15 km/s (-1.87%) in shear wave velocity. We find that the effects of the Mg + Si <=> Al + Fe substitution on the seismic properties of MgSiO3 perovskite and post-perovskite depend on the crystallography of the substitution, namely the position the exchanged cations take in the structure.

  2. The influence of the iron content on the reductive decomposition of A{sub 3−x}Fe{sub x}Al{sub 2}Si{sub 3}O{sub 12} garnets (A = Mg, Mn; 0.47 ≤ x ≤ 2.85)

    SciTech Connect

    Aparicio, Claudia Filip, Jan Mashlan, Miroslav Zboril, Radek

    2014-10-27

    Thermally-induced reductive decomposition of natural iron-bearing garnets of the almandine-pyrope and almandine-spessartine series were studied at temperatures up to 1200 °C (heating rate of 10 °C/min) under atmosphere of forming gas (10% of H{sub 2} in N{sub 2}). Crystallochemical formula of the studied garnet was calculated as {sup VIII}(A{sub 3−x}Fe{sub x}{sup 2+}){sup VI}(Al,Fe{sup 3+}){sub 2}Si{sub 3}O{sub 12}, where the amount of Fe{sup 3+} in the octahedral sites is negligible with the exception of pyrope, A = Mg, Mn, and 0.47 ≤ x ≤ 2.85. The observed decomposition temperature, determined from differential scanning calorimetry and thermogravimetry, is greater than 1000 °C in all cases and showed almost linear dependence on the iron content in the dodecahedral sites of the studied garnets, with the exception of garnet with a near-pyrope composition (Prp{sub 80}Alm{sub 20}). The initial garnet samples and decomposition products were characterized in details by means of X-ray powder diffraction and {sup 57}Fe Mössbauer spectroscopy. We found that all studied garnets have common decomposition products such as metallic iron (in general, rounded particles below 4 μm) and Fe-spinel; the other identified decomposition products depend on starting chemical composition of the garnet: Fe-cordierite, olivine (fayalite or tephroite), cristobalite, pyroxene (enstatite or pigeonite), and anorthite. Anorthite and pigeonite were only present in garnets with Ca in the dodecahedral site. All the identified phases were usually well crystallized.

  3. The puzzling MgAl anticorrelation in globular-cluster red giants: primordial plus deep mixing scenario?

    NASA Astrophysics Data System (ADS)

    Denissenkov, P. A.; Da Costa, G. S.; Norris, J. E.; Weiss, A.

    1998-05-01

    Star-to-star abundance variations of C, N, O, Na and Al in globular-cluster red giants have been recently supplemented by the finding that [Mg/Fe] is depleted in stars with extremely large [Al/Fe] (Shetrone 1996a). To find out which of the magnesium isotopes is responsible for the observed depletion of [Mg/Fe] Shetrone (1996b) also undertook an isotopic analysis of Mg and found that it is (24) Mg which is depleted in Al-rich giants. On the other hand, Norris & Da Costa (1995) demonstrated that even in the massive globular cluster omega Cen which has intrinsic spreads in both [Fe/H] and the abundances of the s-process elements, [O/Fe] anticorrelates with [Na/Fe] and [Al/Fe] as in ``normal'' monometallic clusters. These new spectroscopic results allow us to test current models of stellar evolution and nucleosynthesis, as well as those of the formation and chemical enrichment of globular clusters. In an effort to explain self-consistently these observations we have considered two possibilities: (1) a deep mixing scenario which assumes that in red giants some kind of (extra)mixing transports products of nuclear reactions from the hydrogen burning shell (HBS) to the base of the convective envelope; and (2) a combination of primordial and deep mixing scenarios. It is shown that (1) cannot account for the anticorrelation of [Mg/Fe] vs. [Al/Fe] without additional ad hoc assumptions, among which we identify a strong but still undetected low energy resonance in the reaction (24) Mg(p,gamma )(25) Al, and episodical increases of the HBS temperature up to the value T~ 7410(6) K. In (2) intermediate mass AGB stars are assumed to produce the decreased (24) Mg and increased (25) Mg initial abundances in some globular-cluster low mass stars and Al is synthesized at the expense of (25) Mg in the HBS and transported to the surface of the red giant by extramixing. We discuss advantages and deficiencies of both scenarios and propose some observational tests.

  4. First principles investigation of Fe and Al bearing phase H

    NASA Astrophysics Data System (ADS)

    Tsuchiya, J.; Tsuchiya, T.

    2015-12-01

    The global circulation of water in the earth is important to investigate the evolution history and dynamics of the earth, since the physical properties (e.g. atomic diffusivity, melting temperature, electrical conductivity and seismic velocities) of the constituent minerals are considerably changed by the presence of water. It has been believed that water is carried into the deep Earth's interior by hydrous minerals such as the dense hydrous magnesium silicates (DHMSs) which are also known as alphabet phases (phase A, superhydrous phase B, and phase D etc.) in the descending cold plate. It has been thought that the relay of these hydrous phases was terminated at ~1200 km depth by the dehydration of phase D which was the highest pressure phase of DHMSs. Recently, we have theoretically predicted the high pressure phase of phase D and experimentally confirmed the existence of this new DHMS in lower mantle pressure conditions above ~45 GPa. This phase has MgSiO4H2chemical composition and named as phase H. At the lower mantle pressure conditions, Al and H-bearing SiO2, δ-AlOOH, ɛ-FeOOH and phase H may be the relevant hydrous phases in the subducting slabs. Interestingly, the crystal structure of these hydrous phases are almost same and have CaCl2type structure. This suggests that these hydrous phases may potentially be able to make the wide range of solid solution. Some experimental studies already reported that Al preferentially partitioned into phase H and the stability of phase H drastically increased by incorporation of Al (Nishi et al. 2014, Ohira et al. 2014). The density of subducted MORB is reported to be denser than that of pyrolite in the lower mantle (e.g. Kawai et al. 2009). Therefore, there is a possibility that phase H containing Al and Fe in subducted MORB survive down to the bottom of lower mantle and the melting of phase H at the core mantle boundary may contribute to the cause of ultra-low velocity zones. In this study, we further extends our

  5. The synthesis and hydrogen storage properties of pure nanostructured Mg2FeH6.

    PubMed

    Zhang, Xuanzhou; Yang, Rong; Qu, Jianglan; Zhao, Wei; Xie, Lei; Tian, Wenhuai; Li, Xingguo

    2010-03-01

    In this work, pure nanostructured Mg(2)FeH(6) is successfully synthesized by sintering of a mixture of 2Mg + Fe nanoparticles. The successful preparation of pure Mg(2)FeH(6) can be attributed to the small particle sizes of Mg and Fe nanoparticles prepared by hydrogen plasma-metal reaction (HPMR), which benefits the synthesis. The hydrogen storage properties of Mg(2)FeH(6) and the synthesis mechanism of the Mg-Fe-H system are studied. The sample desorbs 5.0 wt% of hydrogen rapidly in 6 min under an initial hydrogen pressure of approximately 100 Pa at 623 K. The enthalpy and entropy of the reaction are deduced from the equilibrium plateau pressures of the desorption isotherms. The obtained Mg(2)FeH(6) shows favorable hydrogen storage properties due to the specific nanostructure of the materials.

  6. The fracture resistance of 1420 and 1421 Al-Mg-Li alloys

    NASA Technical Reports Server (NTRS)

    Birt, M. J.; Hafley, R. A.; Wagner, J. A.; Lisagor, W. B.

    1993-01-01

    The resistance to stable crack growth in 1420-T6 (Al-5Mg-2.1Li-0.1Zr-0.01Sc, less than 0.06Fe, in wt pct) and 1421-T6 (Al-4.7Mg-1.9Li-0.09Zr-0.2Sc, less than 0.06Fe) Al-Mg-Li alloys was investigated, based on the R curves generated in accordance with ASTM E561-86 and fractography analyses. The crack resistance of 1420 and 1421 alloys was found to be comparable to that of the conventional Space Shuttle External Tank Al alloy, 2219-T87. The main differences in the fracture behaviors arose from differences in the alloys' microstructures. In the case of 1420 alloy, a slightly enhanced toughness behavior was observed, due to the T-phase precipitates, which may have promoted more homogeneous deformation and enhanced microvoid coalescence. In the case of 1421 alloy, the addition of Sc led to a refined grain size and resulted in slightly reduced toughness.

  7. Production of Mg and Al Auger electrons by noble gas ion bombardment of Mg and Al surfaces

    NASA Technical Reports Server (NTRS)

    Ferrante, J.; Pepper, S. V.

    1976-01-01

    Relative production efficiencies of Mg and Al Auger electrons by He, Ne, Ar, Kr, and Xe ion bombardment are reported as a function of ion energy for energies not exceeding 3 keV. The experimental apparatus employed consisted of a LEED-Auger system equipped with an ion gun and a four-grid retarding-potential analyzer. It is found that: (1) the shape of the ion-excited Auger signal was independent of the rare gas and quite symmetric; (2) the Al signal was about an order of magnitude smaller than the Mg signal for a given bombarding species and ion-gun voltage; (3) no signal was observed for He(+) bombardment under any of the experimental conditions; (4) signal strengths were independent of temperature and ion dose; (5) the Auger production efficiencies differed by no more than a factor of two among the different gases - except for He(+) - on a given metal; (6) all the signal strengths increased with increasing ion-gun voltage, with no maximum exhibited; and (7) the apparent threshold energy for the Al signal was higher than that for the Mg signal. The differences between the results for the two metals are attributed to the fact that the Al 2p orbital lies deeper in energy and closer to the nucleus than the corresponding Mg orbital.

  8. Flux pinning behavior of MgB2 doped with Fe and Fe2O3 nanowires

    NASA Astrophysics Data System (ADS)

    Ke, C.; Cheng, C. H.; Yang, Y.; Zhang, Y.; Wang, W. T.; Zhao, Y.

    MgB2 bulks doped with Fe and Fe2O3 nanowires are prepared by hybridized diffusion method. The doping effect on superconductivity transition temperature, Tc, critical current density Jc, and flux pinning behavior have been studied. It is found that both Tc and Jc of MgB2 show quite different features for these two kinds of nanowires. Fe2O3 nanowires significantly suppress both Tc and Jc of MgB2, whereas Fe nanowires do improve the flux pining behavior of MgB2 although the Tc is slightly suppressed.

  9. Divorced Eutectic Solidification of Mg-Al Alloys

    NASA Astrophysics Data System (ADS)

    Monas, Alexander; Shchyglo, Oleg; Kim, Se-Jong; Yim, Chang Dong; Höche, Daniel; Steinbach, Ingo

    2015-08-01

    We present simulations of the nucleation and equiaxed dendritic growth of the primary hexagonal close-packed -Mg phase followed by the nucleation of the -phase in interdendritic regions. A zoomed-in region of a melt channel under eutectic conditions is investigated and compared with experiments. The presented simulations allow prediction of the final properties of an alloy based on process parameters. The obtained results give insight into the solidification processes governing the microstructure formation of Mg-Al alloys, allowing their targeted design for different applications.

  10. Fabrication of Fully Epitaxial CoFe/MgO/CoFe Magnetic Tunnel Junctions on Ge(001) Substrates via a MgO Interlayer

    NASA Astrophysics Data System (ADS)

    Li, Gui-fang; Taira, Tomoyuki; Liu, Hong-xi; Matsuda, Ken-ichi; Uemura, Tetsuya; Yamamoto, Masafumi

    2012-09-01

    Fully epitaxial magnetic tunnel junctions (MTJs) with Co50Fe50 (CoFe) electrodes and a MgO barrier were fabricated on Ge(001) single-crystal substrates via a MgO interlayer. Microfabricated CoFe/MgO/CoFe MTJs with a 10-nm-thick MgO interlayer showed a high tunnel magnetoresistance (TMR) ratio of 218% at 293 K, which is encouraging for monolithic integration of MTJs and Ge field-effect transistors for constructing future-generation nonvolatile logic circuits featuring ultralow-power consumption. Furthermore, MTJs with even a decreased MgO interlayer thickness of 1.0 nm showed a relatively high TMR ratio of 110% at 293 K, suggesting the promise of heterostructures consisting of MTJ/MgO interlayer/Ge(001) as a key device structure for spin injection into a Ge channel from an MTJ.

  11. Microstructure of the Al-La-Ni-Fe system

    SciTech Connect

    Vasil’ev, A. L.; Ivanova, A. G.; Bakhteeva, N. D.; Kolobylina, N. N.; Orekhov, A. S.; Presnyakov, M. Yu.; Todorova, E. V.

    2015-01-15

    The microstructure of alloys based on the Al-La-Ni-Fe system, which are characterized by a unique ability to form metal glasses and nanoscale composites in a wide range of compositions, has been investigated. Al{sub 85}Ni{sub 7}Fe{sub 4}La{sub 4} and Al{sub 85}Ni{sub 9}Fe{sub 2}La{sub 4} alloys have been analyzed by electron microscopy (including high-resolution scanning transmission electron microscopy), energy-dispersive X-ray microanalysis, electron diffraction (ED), and X-ray diffraction (XRD). It is found that, along with fcc Al and Al{sub 4}La (Al{sub 11}La{sub 3}) particles, these alloys contain a ternary phase Al{sub 3}Ni{sub 1−x}Fe{sub x} (sp. gr. Pnma) isostructural to the Al{sub 3}Ni phase and a quaternary phase Al{sub 8}Fe{sub 2−x}Ni{sub x}La isostructural to the Al{sub 8}Fe{sub 2}Eu phase (sp. gr. Pbam). The unit-cell parameters of the Al{sub 3}Ni{sub 1−x}Fe{sub x} and Al{sub 8}Fe{sub 2−x}Ni{sub x}La compounds, determined by ED and refined by XRD, are a = 0.664(1) nm, b = 0.734(1) nm, and c = 0.490(1) nm for Al{sub 3}Ni{sub 1−x}Fe{sub x} and a = 1.258(3) nm, b = 1.448(3) nm, and c = 0.405(8) nm for Al{sub 8}Fe{sub 2−x}Ni{sub x}La. In both cases Ni and Fe atoms are statistically arranged, and no ordering is found. Al{sub 8}Fe{sub 2−x}Ni{sub x}La particles contain inclusions in the form of Al{sub 3}Fe δ layers.

  12. Fe-Mg partitioning between perovskite, post-perovskite, and ferropericlase at the lowermost mantle

    NASA Astrophysics Data System (ADS)

    Sakai, T.; Ohtani, E.; Miyahara, M.; Nishijima, M.; Terasaki, H.; Kondo, T.; Kikegawa, T.; Hirao, N.; Ohishi, Y.

    2007-12-01

    The lower mantle consists mainly of iron-bearing magnesium silicate perovskite and ferropericlase. The Fe-Mg partition coefficient between these minerals is important to understand the chemical and physical properties of the mantle. The lowermost 200 km of the mantle is called D" layer and it is considered to be a thermal and chemical boundary layer between the silicate mantle and outer core. Recent high pressure studies [e.g., Murakami et al., 2004] revealed that (Mg, Fe)SiO3 perovskite transformed to post-perovskite phase at the pressure and temperature conditions of D" layer. In this study, high pressure and high temperature partitioning experiments were performed up to 140 GPa at 2000 K using a laser heated diamond anvil cell (LHDAC). Powdered or single crystalline Al-free San Carlos olivine (Mg0.88, Fe0.12)2SiO4 was used as a starting material in order to avoid complicated compositional effects. The starting material was embedded in sodium chloride which is pressure medium. Pressures were determined by both the ruby fluorescence method [Mao et al., 1978] and the Raman shift of the first-order Raman spectra of diamond anvil [Akahama and Kawamura, 2004]. Temperatures were measured by spectroradiometric method. The recovered samples were analyzed using the technique of combination of FIB and ATEM (JEOL JEM-3000F (FEG TEM-STEM)). The result shows that post- perovskite phase exhibits very small iron content, Fe# = 0.01 at 140 GPa and 2000 K. Therefore, the partition coefficient was K = 0.03, which indicates that iron prefers ferropericlase strongly rather than post-perovskite phase, which is consistent with the prediction of the ab initio calculation [Iitaka et al., 2004], and the high-spin/low- spin transition arguments of ferropericlase [Badro et al., 2003]. Kobayashi et al. (2005) showed higher partitioning coefficient of K= 0.30 in spite of the lower temperature condition of 1600 K compared to the present experiment. They reported that significant iron

  13. Lattice instability in the AlMgB14 structure

    NASA Astrophysics Data System (ADS)

    Wan, L. F.; Beckman, S. P.

    2014-04-01

    The lattice dynamics of the AlMgB14 structure is characterized by phonon vibrational modes that are calculated from first-principles methods. The stoichiometric composition of AlMgB14 is found to have three soft phonon modes, which have displacements associated with metal atoms vibrating against the B lattice. This lattice instability is believed to be associated with the occupation of electronic states in the conduction bands. The off-stoichiometric occupation sweeps the Fermi level from the conduction band into the gap, and as a result the observed soft phonon modes are driven away. Based on a simple electron counting scheme, as also discussed by Mori [39], it is observed that stable XYB14 compounds have between 15 and 16 electrons contributed to the B-lattice from the metal species.

  14. Superconductivity in new iron pnictide oxide Fe2As2Sr4(Mg,Ti)2O6

    NASA Astrophysics Data System (ADS)

    Sato, Shinya; Ogino, Hiraku; Kishio, Kohji; Shimoyama, Jun-Ichi

    2010-03-01

    A new iron arsenide oxide Fe2As2Sr4MgTiO6, which is isostructural with the iron-based superconductor Fe2Pn2Sr4M2O6^[1,2], has been successfully synthesized by the solid-state reaction in quartz ampoules. Fe2As2Sr4MgTiO6 has antifluorite-type iron arsenide layer and K2NiF4-type oxide layer, while the M-site is composed of a combination of divalent (Mg^2+) and tetravalent (Ti^4+) cations as in the case of a double perovskite La(Mg,Ti)O3. This fact indicates chemical flexibility of the perovskite-related layer in this system. This compound showed bulk superconductivity with Tc of ˜20 K by partial substitution of Co for Fe. Moreover, high Tc above 35 K was recorded by samples starting from Co-free and Ti-rich compositions, Fe2As2Sr4(Mg1-xTix)2O6 (x =0.7˜0.8). [1] H. Ogino et al., Supercond. Sci. Technol. 22 (2009) 075008. [2] X. Zhu et al., Phys. Rev. B 79 (2009) 220512(R).

  15. XMCD and XAS examination of cation ordering in synthetic Mg- and Al-substituted titanomagnetites

    NASA Astrophysics Data System (ADS)

    Lappe, S. C. L. L.; Bowles, J.; Jackson, M.; Arenholz, E.

    2015-12-01

    Many paleomagnetic studies use natural magnetic minerals of the titanomagnetite (TM) solid solution series (Fe3-xTixO4, 0 ≤ x ≤ 1). So far our understanding of the acquisition of thermal remanent magnetisation (TRM) in those minerals was based on the assumption that their Curie temperature (TC) only depends on composition. However, it has been shown that TC of some natural TMs with Al- and Mg-substitution also strongly depends on thermal history and TC changes up to >150°C on timescales and at temperatures relevant to laboratory and geological processes were observed (Bowles et al. 2013). These variations in TC are thought to result from cation reordering within the crystal lattice. Those processes may have major effects on the acquisition, retention and demagnetisation of partial TRM and thermoviscous remanence and may have significant consequences for many paleomagnetic studies. However, so far no direct evidence for this cation reordering has been established. To gain further insight into the mechanisms at work, we have synthesised TMs of varying Ti-content (0.25 ≤ x ≤ 60) and with different degrees of Al- and Mg- substitution. Measuring the magnetic susceptibility as function of temperature TC was determined. Subsequently the samples were subjected to isothermal annealing at temperatures between 325-400°C for 10 to 103 hours. We observe an increase of TC on warming with anneal time up to 80°, whereas TC on cooling decreases slightly. The magnitude of the change in TC on warming varies with anneal temperature, and the temperature of maximum change depends on composition. Splits of the samples were studied using X-ray magnetic circular dichroism (XMCD) of the Fe L2,3-edge, which is sensitive to valence state and site occupancy of the Fe cations. The results suggest different Fe2+/Fe3+ site occupancy for different sample compositions but there seem to be no consistent differences between the XMCD spectra of annealed and un-annealed samples of one

  16. {sup 60}Fe AND {sup 26}Al IN CHONDRULES FROM UNEQUILIBRATED CHONDRITES: IMPLICATIONS FOR EARLY SOLAR SYSTEM PROCESSES

    SciTech Connect

    Mishra, R. K.; Goswami, J. N.; Rudraswami, N. G.; Tachibana, S.; Huss, G. R.

    2010-05-10

    The presence of about a dozen short-lived nuclides in the early solar system, including {sup 60}Fe and {sup 26}Al, has been established from isotopic studies of meteorite samples. An accurate estimation of solar system initial abundance of {sup 60}Fe, a distinct product of stellar nucleosynthesis, is important to infer the stellar source of this nuclide. Previous studies in this regard suffered from the lack of exact knowledge of the time of formation of the analyzed meteorite samples. We present here results obtained from the first combined study of {sup 60}Fe and {sup 26}Al records in early solar system objects to remove this ambiguity. Chondrules from unequilibrated ordinary chondrites belonging to low petrologic grades were analyzed for their Fe-Ni and Al-Mg isotope systematics. The Al-Mg isotope data provide the time of formation of the analyzed chondrules relative to the first solar system solids, the Ca-Al-rich inclusions. The inferred initial {sup 60}Fe/{sup 56}Fe values of four chondrules, combined with their time of formation based on Al-Mg isotope data, yielded a weighted mean value of (6.3 {+-} 2) x 10{sup -7} for solar system initial {sup 60}Fe/{sup 56}Fe. This argues for a high-mass supernova as the source of {sup 60}Fe along with {sup 26}Al and several other short-lived nuclides present in the early solar system.

  17. Synthesis and characterization of Mn intercalated Mg-Al hydrotalcite.

    PubMed

    Yang, Chengxue; Liao, Libing; Lv, Guocheng; Wu, Limei; Mei, Lefu; Li, Zhaohui

    2016-10-01

    Mn intercalated hydrotalcite was prepared using a reconstruction method. And Mn intercalation was confirmed by XRD, FTIR, and thermal analyses. The different valences of Mn were present as determined by XPS. Calcination slightly promoted the isomorphic replacement of Mn(2+) and Mn(3+) for Mg(2+) and Al(3+), especially the replacement of Mn(2+) for Mg(2+) and Al(3+), and to some extent, reduced Mn intercalation. Ultrasonic treatment significantly increased Mn intercalation in permanganate form (Mn(7+)), and promoted the replacement of Mn(2+) for Mg(2+) and Al(3+). XRF analysis showed that ultrasonic treatment decreased the unbalanced layer charge of Mn intercalated hydrotalcite, while prolonged calcination increased it. These results may provide guidance on the preparation and application of Mn intercalated hydrotalcite. Extended calcination time and ultrasonic vibration increased the interlayer spacing of hydrotalcite, as a result of reduction in layer charge. As the layer charge was not completely balanced after Mn intercalation, a certain amount of CO3(2-) was re-adsorbed into the interlayer space. Mn-hydrotalcites with different layer charges, different contents of Mn with varying valences are expected to have different performances in the process of adsorption, degradation, and catalysis. PMID:27380016

  18. Synthesis and characterization of Mn intercalated Mg-Al hydrotalcite.

    PubMed

    Yang, Chengxue; Liao, Libing; Lv, Guocheng; Wu, Limei; Mei, Lefu; Li, Zhaohui

    2016-10-01

    Mn intercalated hydrotalcite was prepared using a reconstruction method. And Mn intercalation was confirmed by XRD, FTIR, and thermal analyses. The different valences of Mn were present as determined by XPS. Calcination slightly promoted the isomorphic replacement of Mn(2+) and Mn(3+) for Mg(2+) and Al(3+), especially the replacement of Mn(2+) for Mg(2+) and Al(3+), and to some extent, reduced Mn intercalation. Ultrasonic treatment significantly increased Mn intercalation in permanganate form (Mn(7+)), and promoted the replacement of Mn(2+) for Mg(2+) and Al(3+). XRF analysis showed that ultrasonic treatment decreased the unbalanced layer charge of Mn intercalated hydrotalcite, while prolonged calcination increased it. These results may provide guidance on the preparation and application of Mn intercalated hydrotalcite. Extended calcination time and ultrasonic vibration increased the interlayer spacing of hydrotalcite, as a result of reduction in layer charge. As the layer charge was not completely balanced after Mn intercalation, a certain amount of CO3(2-) was re-adsorbed into the interlayer space. Mn-hydrotalcites with different layer charges, different contents of Mn with varying valences are expected to have different performances in the process of adsorption, degradation, and catalysis.

  19. Microstructure evolution and properties of Al/Al-Mg-Si alloy clad wire during heat treatment

    NASA Astrophysics Data System (ADS)

    Wang, Xiang; Guan, Ren-guo; Zhang, Yang; Su, Ning; Ji, Lian-ze; Li, Yuan-dong; Chen, Ti-jun

    2016-06-01

    In this paper, heat treatment was carried out on Al/Al-Mg-Si alloy clad wire, and microstructure evolution and properties of Al/Al-Mg-Si alloy clad wire during heat treatment were investigated. During solution, contents of Mg and Si in inner matrix increased due to dissolution of primary Mg2Si, and they also increased in outer matrix because Mg and Si diffused across the interface. Tensile strength of the clad wire increased firstly and then decreased, and elongation continuously increased, while conductivity continuously decreased with the increase in solution time. In aging process, Mg2Si precipitated in both inner core and outer layer, and the content and average diameter of the precipitate increased with the increase in aging time. The content of precipitate was higher, and the average diameter was bigger in inner core. Tensile strength of the clad wire increased firstly and then decreased with the increase in aging time, and the elongation continuously decreased, while the conductivity continuously increased. The peak tensile strength of 202 MPa occurred at 8 h, when the corresponding elongation was 20 % and the conductivity reached 56.07 %IACS. Even tensile strength of the prepared clad wire approximately equaled to that of Al-0.5Mg-0.35Si alloy 203 MPa, the conductivity was obviously improved from 54.2 to 56.07 %IACS.

  20. Structure determination of Fe-Al-Ge alloys

    NASA Astrophysics Data System (ADS)

    Gargicevich, D.; Galván Josa, V. M.; Blanco, C.; Lambri, A.; Cuello, G. J.

    2015-11-01

    We studied the crystalline structure of Fe - 8at.%Al - 4at.%Ge alloy between 300 and 1300 K and its relation to the mechanical response by means of neutron diffraction and mechanical spectroscopy. At room temperature we observe a Fe3Al-type ordered structure with a deficiency of Al in the 8c sites. The Ge atoms are distributed in the 4a and Al atoms in 8c sites. At high temperature we observe an order-disorder transformation when the crystal structure becomes Fe-α type. This loss of order gives rise to the hysteresis behavior of damping between the heating and cooling runs.

  1. Fe-Mg diffusion chronometry in orthopyroxene from the Minoan eruption of Santorini, Greece

    NASA Astrophysics Data System (ADS)

    Flaherty, Taya; Druitt, Tim; Fabbro, Gareth; Costa, Fidel; Preece, Katie; Deering, Chad

    2016-04-01

    Constraining the timescales governing magma ascent and storage prior to ignimbrite eruptions is crucial for understanding the behaviour of caldera volcanoes. Diffusion chronometry provides estimates of the pre-eruptive residence times of crystals at magmatic temperatures, and hence of the longevities of bodies of crystal-bearing magma that are finally discharged. We have used Fe-Mg diffusion chronometry in orthopyroxene (opx) crystals from the Minoan eruption of Santorini in order to calculate the pre-eruptive residence times of these crystals. The Minoan eruption occurred in the late 17th century BCE, and discharged 30-80 km3 of rhyodacitic magma containing about 10 vol.% of plagioclase, opx, cpx and Fe-Ti oxides. The orthopyroxenes have compositions of Wo2‑3En52‑70Fs28‑45 (#Mg = 0.53-0.65) with Al2O3 contents typically <0.5 wt.%, and include normally zoned, reversely zoned and unzoned types. Compositional images reveal sector zoned morphologies with Al-rich prismatic zones and Al-poor terminations, possibly indicative of rapid growth. Representative opx crystals were extracted from pumices and mounted in epoxy grain mounts. High-resolution backscattered electron images of zoned crystals with greyscale values calibrated for Mg# were used to identify Fe-Mg gradients across zone boundaries, which were then modelled as diffusion gradients using published diffusion coefficients for Mg-Fe interdiffusion within the a-b plane of opx, a magmatic temperature (855 ± 25 ° C) and fO2 determined from touching magnetite-ilmenite pairs in the same rock. Our models assumed initial step functions in Mg and Fe concentrations, and that any non-zero width is a result of diffusion. The time required for to reach the observed width of diffusion at 855° C was taken to be a maximum residence time, and was calculated for a total of 22 zone boundaries from 13 crystals. Profiles were taken perpendicular to the crystal length, within the a-b crystallographic plane. Only zone

  2. Fe-Mg diffusion chronometry in orthopyroxene from the Minoan eruption of Santorini, Greece

    NASA Astrophysics Data System (ADS)

    Flaherty, Taya; Druitt, Tim; Fabbro, Gareth; Costa, Fidel; Preece, Katie; Deering, Chad

    2016-04-01

    Constraining the timescales governing magma ascent and storage prior to ignimbrite eruptions is crucial for understanding the behaviour of caldera volcanoes. Diffusion chronometry provides estimates of the pre-eruptive residence times of crystals at magmatic temperatures, and hence of the longevities of bodies of crystal-bearing magma that are finally discharged. We have used Fe-Mg diffusion chronometry in orthopyroxene (opx) crystals from the Minoan eruption of Santorini in order to calculate the pre-eruptive residence times of these crystals. The Minoan eruption occurred in the late 17th century BCE, and discharged 30-80 km3 of rhyodacitic magma containing about 10 vol.% of plagioclase, opx, cpx and Fe-Ti oxides. The orthopyroxenes have compositions of Wo2-3En52-70Fs28-45 (#Mg = 0.53-0.65) with Al2O3 contents typically <0.5 wt.%, and include normally zoned, reversely zoned and unzoned types. Compositional images reveal sector zoned morphologies with Al-rich prismatic zones and Al-poor terminations, possibly indicative of rapid growth. Representative opx crystals were extracted from pumices and mounted in epoxy grain mounts. High-resolution backscattered electron images of zoned crystals with greyscale values calibrated for Mg# were used to identify Fe-Mg gradients across zone boundaries, which were then modelled as diffusion gradients using published diffusion coefficients for Mg-Fe interdiffusion within the a-b plane of opx, a magmatic temperature (855 ± 25 ° C) and fO2 determined from touching magnetite-ilmenite pairs in the same rock. Our models assumed initial step functions in Mg and Fe concentrations, and that any non-zero width is a result of diffusion. The time required for to reach the observed width of diffusion at 855° C was taken to be a maximum residence time, and was calculated for a total of 22 zone boundaries from 13 crystals. Profiles were taken perpendicular to the crystal length, within the a-b crystallographic plane. Only zone boundaries

  3. Theory of perpendicular magnetocrystalline anisotropy in Fe/MgO (001)

    NASA Astrophysics Data System (ADS)

    Odkhuu, Dorj; Yun, Won Seok; Rhim, S. H.; Hong, Soon Cheol

    2016-09-01

    The origin of large perpendicular magnetocrystalline anisotropy (PMCA) in Fe/MgO (001) is revealed by comparing Fe layers with and without the MgO. Although Fe-O p-d hybridization is weakly present, it cannot be the main origin of the large PMCA as claimed in previous study. Instead, perfect epitaxy of Fe on the MgO is more important to achieve such large PMCA. As an evidence, we show that the surface layer in a clean free-standing Fe (001) dominantly contributes to EMCA, while in the Fe/MgO, those by the surface and the interface Fe layers contribute almost equally. The presence of MgO does not change positive contribution from < xz |ℓZ | yz >, wherease it reduces negative contribution from and < xy |ℓX | xz , yz >.

  4. Microstructure evolution of Al-Mg-B thin films by thermal annealing

    NASA Astrophysics Data System (ADS)

    Tian, Y.; Constant, A.; Lo, C. C. H.; Anderegg, J. W.; Russell, A. M.; Snyder, J. E.; Molian, P.

    2003-07-01

    The growth of Al-Mg-B thin films on SiO2/Si(100) substrates was performed by nanosecond pulsed laser deposition at three different substrate temperatures (300 K, 573 K, and 873 K). The as-deposited films were then annealed at 1173 K or 1273 K for 2 h. X-ray photoelectron spectroscopy, x-ray diffraction (XRD), and atomic force microscope were employed to investigate the effects of processing conditions on the composition, microstructure evolution, and surface morphology of the Al-Mg-B films. The substrate temperatures were found to affect the composition of as-deposited films in that the Mg content decreases and C content increases at higher substrate temperatures, in particular for the 873 K-deposited film. XRD results show that the as-deposited films were amorphous, and this structure may be stable up to 1173 K. Annealing at 1273 K was found to fully crystallize the room temperature and 573 K-deposited Al-Mg-B films with the formation of the polycrystalline orthorhombic AlMgB14 phase, accompanied by the development of a pronounced (011) preferred orientation. Nevertheless, high C incorporation in the 873 K-deposited Al-Mg-B film inhibits the crystallization and the amorphous structure remains stable even during 1273 K annealing. The presence of Si in the room-temperature-deposited 1273 K-annealed film due to the interdiffusion between the substrate and film leads to the formation of an additional tetragonal α-FeSi2 phase, which is thought to cause the surface cracking and microstructural instability observed in this film.

  5. Strength anomaly in B2 FeAl single crystals

    SciTech Connect

    Yoshimi, K.; Hanada, S.; Yoo, M.H.; Matsumoto, N.

    1994-12-31

    Strength and deformation microstructure of B2 Fe-39 and 48%Al single crystals (composition given in atomic percent), which were fully annealed to remove frozen-in vacancies, have been investigated at temperatures between room temperature and 1073K. The hardness of as-homogenized Fe-48Al is higher than that of as-homogenized Fe-39Al while after additional annealing at 698K the hardness of Fe-48Al becomes lower than that of Fe-39Al. Fe-39Al single crystals slowly cooled after homogenizing at a high temperature were deformed in compression as a function of temperature and crystal orientation. A peak of yield strength appears around 0.5T{sub m} (T{sub m} = melting temperature). The orientation dependence of the critical resolved shear stress does not obey Schmid`s law even at room temperature and is quite different from that of b.c.c. metals and B2 intermetallics at low temperatures. At the peak temperature slip transition from <111>-type to <001>-type is found to occur macroscopically and microscopically, while it is observed in TEM that some of the [111] dislocations decompose into [101] and [010] on the (1096I) plane below the peak temperature. The physical sources for the positive temperature dependence of yield stress of B2 FeAl are discussed based on the obtained results.

  6. Dirac cones in artificial structures of 3d transitional-metals doped Mg-Al spinels

    SciTech Connect

    Lu, Yuan; Zuo, Xu; Feng, Min; Shao, Bin

    2014-05-07

    Motivated by recent theoretical predications for Dirac cone in two-dimensional (2D) triangular lattice [H. Ishizuka, Phys. Rev. Lett. 109, 237207 (2012)], first-principles studies are performed to predict Dirac cones in artificial structures of 3d transitional-metals (TM = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) doped Mg-Al spinels. In investigated artificial structures, TM dopants substitute specific positions of the B sub-lattice in Mg-Al spinel, and form a quasi-2D triangular lattice in the a-b plane. Calculated results illustrate the existence of the spin-polarized Dirac cones formed in d-wave bands at (around) the K-point in the momentum space. The study provides a promising route for engineering Dirac physics in condensed matters.

  7. Al-26-Mg-26 ages of iron meteorites

    NASA Technical Reports Server (NTRS)

    Herzog, G. F.; Souzis, A. E.; Xue, S.; Klein, J.; Juenemann, D.; Middleton, R.

    1993-01-01

    An exposure age for an iron meteorite can be calculated from measurements of a radioactive nuclide and a stable nuclide that are produced by similar sets of nuclear reactions, provided that the stable nuclide is present with low initial abundance. The standard methods rely on either K-40 (t(sub 1/2) = 1.26 Gy), K-39, and K-41 or on a shorter-lived radionuclide and a stable, noble gas isotope. Widely used pairs of this type include Cl-36/Ar-36 and Al-26/Ne-21. Other pairs that may serve the purpose for iron meteorites contain many stable isotopes besides those of K and the noble gases that are produced partly by cosmic rays. We consider here the calculation of exposure ages, t(sub 26), from measurements of Al-26 (t(sub 1/2) = 0.7 My) and (stable) Mg-26. Ages based on Al-26/Mg-26 ratios, like those based on Cl-36/Ar-36 ratios, are 'buffered' against changes in relative production rates due to shielding because decay of the radioactive nuclide accounts for a good part of the inventory of the stable nuclide.

  8. Fabric cutting application of FeAl-based alloys

    SciTech Connect

    Sikka, V.K.; Blue, C.A.; Sklad, S.P.; Deevi, S.C.; Shih, H.R.

    1998-11-01

    Four intermetallic-based alloys were evaluated for cutting blade applications. These alloys included Fe{sub 3}Al-based (FAS-II and FA-129), FeAl-based (PM-60), and Ni{sub 3}Al-based (IC-50). These alloys were of interest because of their much higher work-hardening rates than the conventionally used carbon and stainless steels. The FeAl-based PM-60 alloy was of further interest because of its hardening possibility through retention of vacancies. The vacancy retention treatment is much simpler than the heat treatments used for hardening of steel blades. Blades of four intermetallic alloys and commercially used M2 tool steel blades were evaluated under identical conditions to cut two-ply heavy paper. Comparative results under identical conditions revealed that the FeAl-based alloy PM-60 outperformed the other intermetallic alloys and was equal to or somewhat better than the commercially used M2 tool steel.

  9. Spin states of ferric iron in Al-bearing Mg-perovskite and post-Mg-perovskite in the lower mantle

    NASA Astrophysics Data System (ADS)

    Fujino, K.; Hamane, D.; Seto, Y.; Nagai, T.; Shinmei, T.; Whitaker, M. L.; Kuwayama, Y.; Ohfuji, H.; Irifune, T.; Hiraoka, N.; Ishii, H.

    2011-12-01

    Pressure-induced high spin (HS) - low spin (LS) transitions of iron in the lower mantle minerals are the key issue to understand the mineral behaviors and dynamics of the lower mantle. However, the spin transitions of iron in Mg-perovskite (Pv) and post-Mg-perovskite (PPv) are still unclear because of the large discrepancies of the results for Pv and very limited reports for PPv. These problems seem to originate partly from the poor quality and/or characterization of the samples for Pv and the experimental difficulty for PPv. We examined the spin states of ferric iron in Al-bearing Pv (up to 200 GPa) and PPv (up to165 GPa) by X-ray emission spectroscopy at room temperature and XRD, using the well qualified samples of the composition Mg0.85Fe3+0.15Al0.15Si0.85O3 loaded in a diamond anvil cell. The reason to have chosen this composition is because the recent studies indicate that Fe3+ is more dominant than Fe2+ and the coupled substitution, Mg + Si → Fe3+ + Al, occurs in lower mantle Pv and PPv. The results indicate that in Pv Fe3+ occupies the 8-coordinated (A) site and is HS below ~50 GPa but above 50-60 GPa it replaces Al at the 6-coordinated (B) site by annealing and becomes LS, while Fe3+ remaining at the A site is HS up to 200 GPa. Meanwhile in PPv Fe3+ occupies the B site and is LS at 165 GPa and it becomes HS between 80 - 40 GPa during decompression from 165 GPa without annealing. We think that the cation exchange reaction of Fe3+ and Al between the A and B sites plays an important role in the spin transition of Fe3+. From these results combined with the recent reports, the spin states of iron in lower mantle Pv and PPv are estimated to be as follows, when we assume that the spin transition pressure of Fe2+ is higher than that of Fe3+ at the same site. In Pv Fe2+ occupies the A site and is HS for the whole lower mantle, while Fe3+ occupies the A site and is HS below ~50 GPa but above 50-60 GPa it replaces Al at the B site and becomes LS. Meanwhile in PPv Fe

  10. Metastability in the MgAl2O4-Al2O3 System

    DOE PAGES

    Wilkerson, Kelley R.; Smith, Jeffrey D.; Hemrick, James G.

    2014-07-22

    Aluminum oxide must take a spinel form ( γ-Al2O3) at elevated temperatures in order for extensive solid solution to form between MgAl2O4 and α-Al2O3. The solvus line between MgAl2O4 and Al2O3 has been defined at 79.6 wt% Al2O3 at 1500°C, 83.0 wt% Al2O3 at 1600°C, and 86.5 wt% Al2O3 at 1700°C. A metastable region has been defined at temperatures up to 1700°C which could have significant implications for material processing and properties. Additionally, initial processing could have major implications on final chemistry. The spinel solid solution region has been extended to form an infinite solid solution with Al2O3 at elevatedmore » temperatures. A minimum in melting at 1975°C and a chemistry of 96 wt% Al2O3 rather than a eutectic is present, resulting in no eutectic crystal formation during solidification.« less

  11. Oxidation of Fe-Cr-Al and Fe-Cr-Al-Y Single Crystals

    NASA Astrophysics Data System (ADS)

    Grabke, H. J.; Siegers, M.; Tolpygo, V. K.

    1995-03-01

    Single crystal samples of the alloy Fe-20%Cr-5%Al with and without Y-doping were used to study the "reactive element" (RE) effect, which causes improved oxidation behaviour and formation of a protective Al2O3 layer on this alloy. The oxidation was followed by AES at 10-7 mbar O2 up to about 1000 °C. Most observations were peculiar for this low pO2 environment, but yttrium clearly favors the formation of Al-oxide and stabilizes it also under these conditions, probably by favoring its nucleation. The oxides formed are surface compounds of about monolayer thickness, not clearly related to bulk oxides. Furthermore, the morphologies of oxide scales were investigated by SEM, after oxidation at 1000°C for 100 h at 133 mbar O2. On Fe-Cr-Al the scale is strongly convoluted and tends to spalling, whereas the presence of Y leads to flat scales which are well adherent. This difference is explained by a change in growth mechanism. The tendency for separation of oxide and metal was highest for the samples with low energy metal surface, i.e. (100) and (110), the scale was better adherent on the (111) oriented surface and on the polycrystalline specimen, since in the latter cases the overall energy for scale/metal separation is higher. All observations, from the low and from the high pO2 experiments, are discussed in relation to the approximately ten mechanisms proposed in the literature for explanation of the RE effects.

  12. Oxidation behavior of FeAl+Hf,Zr,B

    NASA Technical Reports Server (NTRS)

    Smialek, James L.; Doychak, Joseph

    1988-01-01

    The oxidation behavior of Fe-40Al-1Hf, Fe-40Al-1Hf-0.4B, and Fe-40Al-0.1Zr-0.4B (at. percent) alloys was characterized after 900, 1000, and 100 C exposures. Isothermal tests revealed parabolic kinetics after a period of transitional theta-alumina scale growth. The parabolic growth rates for the subsequent alpha-alumina scales were about five times higher than those for NiAl+0.1Zr alloys. The isothermally grown scales showed a propensity toward massive scale spallation due to both extensive rumpling from growth stresses and to an inner layer of HfO2. Cyclic oxidation for 200 1-hr cycles produced little degradation at 900 or 1000 C, but caused significant spallation at 1100 C in the form of small segments of the outer scale. The major difference in the cyclic oxidation of the three FeAl alloys was increased initial spallation for FeAl+Zr,B. Although these FeAl alloys showed many similarities to NiAl alloys, they were generally less oxidation resistant. It is believed that this resulted from nonoptimal levels of dopants and larger thermal expansion mismatch stresses.

  13. Thermal stability of Al-Cu-Fe icosahedral alloys

    NASA Astrophysics Data System (ADS)

    Bessière, M.; Quivy, A.; Lefebvre, S.; Devaud-Rzepski, J.; Calvayrac, Y.

    1991-12-01

    A stable ideally quasiperiodic phase exists in a small range of concentration, close to the composition Al{62}Cu{25.5}Fe{12.5}. Reducing the iron content, or replacing small amounts of copper by aluminium, lead to icosahedral alloys which exhibit around 650 ^{circ}C structural transformations of unclear nature: in the X-ray powder diffraction pattern, the peak profiles become purely Lorentzian (Al{62.3}Cu{25.3}Fe{12.4}) or diffuse “side-bands” appear in the tails of the Bragg peaks (Al{63}Cu{24.5}Fe{12.5}). In the last case long annealing treatments eventually transform the Bragg peaks into diffuse peaks located at positions clearly off the ideal icosahedral symmetry. Small deviations from this composition range lead to Bragg peaks with shoulders whatever the heat-treatment may be; perfect icosahedral order is never obtained for these compositions (Al{63,25}Cu{24,5}Fe{12,25}, Al{64}Cu{24}Fe{12}, Al{63}Cu{25}Fe{12}). Une phase stable idéalement quasipériodique existe dans un petit domaine de concentration, au voisinage de la composition Al{62}Cu{25,5}Fe{12,5}. La diminution de la teneur en fer, ou le remplacement de faibles quantités de cuivre par de l'aluminium, conduisent à des alliages icosaédriques qui subissent vers 650 ^{circ}C des transformations structurales dont la nature n'est pas clairement identifiée: dans le diagramme de diffraction des rayons X sur poudre, les profils de raies deviennent purement Lorentziens (Al{62,3}Cu{25,3}Fe{12,4}) ou bien des raies diffuses apparaissent dans le pied des pics de Bragg (Al{63}Cu{24,5}Fe{12,5}). Dans ce dernier cas un long traitement de recuit transforme finalement les pics de Bragg en des pics diffus localisés à des positions clairement en dehors de celles correspondant à la symétrie icosaédrique idéale. De faibles écarts à ce domaine de compositions conduisent à des diagrammes de rayons X où les pics de Bragg sont épaulés quel que soit le traitement thermique ; l'ordre icosaédrique parfait n

  14. Lubrication performance and mechanisms of Mg/Al-, Zn/Al-, and Zn/Mg/Al-layered double hydroxide nanoparticles as lubricant additives

    NASA Astrophysics Data System (ADS)

    Li, Shuo; Bhushan, Bharat

    2016-08-01

    Solid lubricant particles are commonly used as oil additives for low friction and wear. Mg/Al-, Zn/Al-, and Zn/Mg/Al-layered double hydroxides (LDH) were synthesized by coprecipitation method. The benefits of LDH nanoparticles are that they can be synthesized using chemical methods where size and shape can be controlled, and can be modified organically to allow dispersal in fluids. The LDH nanoparticles were characterized by X-ray diffraction, scanning electron microscope, thermogravimetry, and differential scanning calorimetry. A pin-on-disk friction and wear tester was used for evaluating the friction and wear properties of LDH nanoparticles as lubricant additives. LDH nanoparticles have friction-reducing and anti-wear properties compared to oil without LDHs. Mg/Al-LDH has the best lubrication, possibly due to better thermal stability in severe conditions.

  15. Phosphorus Equilibrium Between Liquid Iron and CaO-SiO2-MgO-Al2O3-FeO-P2O5 Slag Part 1: Literature Review, Methodology, and BOF Slags

    NASA Astrophysics Data System (ADS)

    Assis, Andre N.; Tayeb, Mohammed A.; Sridhar, Seetharaman; Fruehan, Richard J.

    2015-10-01

    Although the phosphorus reaction in steelmaking has been extensively studied, it continues to be a relevant topic as low phosphorus iron sources become less available and more expensive, necessitating the need for more accurate predictions of the partitioning of phosphorous as function of slag composition and temperature. The current study revisits some of the relevant literature on the topic and details the methodology and experimental setup used in recent studies on phosphorus equilibrium between liquid iron and slags. New data for BOF-type slags are presented, where equilibrium was approached from both metal and slag sides i.e., phosphorus was transferred from metal to slag and vice versa. It was found that slags with basicities higher than 2.5 and FeO contents around 20 to 25 wt pct can promote extensive dephosphorization, and high L P, ((pct P)/[pct P]), values were observed i.e., greater than 500.

  16. Solid Solution Effects on the MgAl2O4-MgGa2O4 System

    SciTech Connect

    O'Hara, Kelley; Smith, Jeffrey D; Hemrick, James Gordon

    2009-01-01

    Phase relations between two spinel compounds (MgAl2O4 and MgGa2O4) were studied. Stoichiometric MgAl2O4 was formed in the laboratory through a coprecipitation method. Complete solid solution formation int eh MgAl2O4-MgGa2O4 systems was confirmed through X-ray diffraction analysis. Solid solution between MgAl2O4-MgGa2O4 decreases thermal conductivity at all temperatures up to 900oC. At 200oC with 10 mol% additoin of MgGa2O4 thermal conductivity decreases approximately 25%, and at 900oC there was still an 8% decrease. Additionally, preliminary studies show that porosity between 5% and 10% does not have an appreciable effect on the thermal conductivity in this study.

  17. Tensile Property of Al-Mg-Sc-Zr Alloy at Cryogenic Temperature

    NASA Astrophysics Data System (ADS)

    Zhao, W. T.; Yan, D. S.; Li, X. Y.; Rong, L. J.; Li, Y. Y.

    2006-03-01

    The tensile property and fracture characteristic of Al-Mg-Sc-Zr alloy have been investigated at 77 K, 123 K, 173 K, 223 K and 300 K respectively. Both the strength and elongation improved with decreasing temperature from 300 K to 77 K, particularly between 123 K and 77 K. However, the reduction of area exhibited a maximum at around 173 K. The fractographs of tensile specimens show a completely dimple-type ductile mode of fracture at 77 K and mixed type of fracture at 300 K, and the primary Al3(Sc,Zr) and Al6(Mn,Fe) phases are responsible for void and crack initiation at their interface with the matrix at cryogenic temperature.

  18. Physical and Microstructure Properties of MgAl2C2 Matrix Composite Coating on Titanium

    NASA Astrophysics Data System (ADS)

    Li, Peng

    2014-12-01

    This work is based on the dry sliding wear of the MgAl2C2-TiB2-FeSi composite coating deposited on a pure Ti using a laser cladding technique. Scanning electron microscope images indicate that the nanocrystals and amorphous phases are produced in such coating. X-ray diffraction result indicated that such coating mainly consists of MgAl2C2, Ti-B, Ti-Si, Fe-Al, Ti3SiC2, TiC and amorphous phases. The high resolution transmission electron microscope image indicated that the TiB nanorods were produced in the coating, which were surrounded by other fine precipitates, favoring the formation of a fine microstructure. With increase of the laser power from 0.85 kW to 1.00 kW, the micro-hardness decreased from 1350 1450 HV0.2 to 1200 1300 HV0.2. The wear volume loss of the laser clad coating was 1/7 of pure Ti.

  19. Rutherford Backscattering and Channeling Studies of Mg and Fe Diffusion at the Interface of gamma-Fe₂O₃(001)/MgO(001)

    SciTech Connect

    Thevuthasan, Suntharampillai; Jiang, Weilin; McCready, David E.; Chambers, Scott A.

    1999-12-01

    Investigates the crystalline quality of an epitaxially grown gamma-FeO(001) film on Mg/O(001) substrate along with the Mg and Fe inter-diffusion using Rutherford Backscattering and channeling experiments.

  20. Calcined Mg-Fe layered double hydroxide as an absorber for the removal of methyl orange

    SciTech Connect

    Peng, Chao; Dai, Jing; Yu, Jianying; Yin, Jian

    2015-05-15

    In this work, methyl orange (MO) was effectively removed from aqueous solution with the calcined product of hydrothermal synthesized Mg/Fe layered double hydroxide (Mg/Fe-LDH). The structure, composition, morphology and textural properties of the Mg/Fe-LDH before and after adsorption were characterized by X-ray diffraction, Fourier transformation infrared spectroscopy, transmission electron microscopy, nitrogen adsorption apparatus and X-ray photoelectron spectroscopy. It was confirmed that MO had been absorbed by calcined Mg/Fe-LDH which had strong interactions with MO. The adsorption of MO onto the Mg/Fe-LDH was systematically investigated by batch tests. The adsorption capacity of the Mg/Fe-LDH toward MO was found to be 194.9 mg • g{sup −1}. Adsorption kinetics and isotherm studies revealed that the adsorption of MO onto Mg/Fe-LDH was a spontaneous and endothermic process. These results indicate that Mg/Fe-LDH is a promising material for the removal of MO.

  1. Calcined Mg-Fe layered double hydroxide as an absorber for the removal of methyl orange

    NASA Astrophysics Data System (ADS)

    Peng, Chao; Dai, Jing; Yu, Jianying; Yin, Jian

    2015-05-01

    In this work, methyl orange (MO) was effectively removed from aqueous solution with the calcined product of hydrothermal synthesized Mg/Fe layered double hydroxide (Mg/Fe-LDH). The structure, composition, morphology and textural properties of the Mg/Fe-LDH before and after adsorption were characterized by X-ray diffraction, Fourier transformation infrared spectroscopy, transmission electron microscopy, nitrogen adsorption apparatus and X-ray photoelectron spectroscopy. It was confirmed that MO had been absorbed by calcined Mg/Fe-LDH which had strong interactions with MO. The adsorption of MO onto the Mg/Fe-LDH was systematically investigated by batch tests. The adsorption capacity of the Mg/Fe-LDH toward MO was found to be 194.9 mg • g-1. Adsorption kinetics and isotherm studies revealed that the adsorption of MO onto Mg/Fe-LDH was a spontaneous and endothermic process. These results indicate that Mg/Fe-LDH is a promising material for the removal of MO.

  2. Effects of Be, Sr, Fe and Mg interactions on the microstructure and mechanical properties of aluminum based aeronautical alloys

    NASA Astrophysics Data System (ADS)

    Ibrahim, Mohamed Fawzy

    The present work was carried out on a series of heat-treatable aluminum-based aeronautical alloys containing various amounts of magnesium (Mg), iron (Fe), strontium (Sr) and beryllium (Be). Tensile test bars (dendrite arm spacing ~ 24mum) were solutionized for either 5 or 12 hours at 540°C, followed by quenching in warm water (60°C). Subsequently, these quenched samples were aged at 160°C for times up to 12 hours. Microstructural assessment was performed. All heat-treated samples were pulled to fracture at room temperature using a servo-hydraulic tensile testing machine. The results show that Be causes partial modification of the eutectic silicon (Si) particles similar to that reported for Mg addition. Addition of 0.8 wt.% Mg reduced the eutectic temperature by ~10°C. During solidification of alloys containing high levels of Fe and Mg, without Sr, a peak corresponding to the formation of a Be-Fe phase (Al8Fe2BeSi) was detected at 611°C. The Be-Fe phase precipitates in a script-like morphology. A new quinary eutectic-like reaction was observed to take place near the end of solidification of high Mg, high Fe, Be-containing alloys. This new reaction is composed mainly of fine particles of Si, Mg2Si, pi-Al 8Mg3FeSi6 and (Be-Fe) phases. The volume fraction of this reaction decreased with the addition of Sr. The addition of Be has a noticeable effect on decreasing the beta-phase length, or volume fraction, this effect may be limited by adding Sr. Beryllium addition also results in the precipitation of the beta-phase in a nodular form, which reduces the harmful effects of these intermetallics on the alloy mechanical properties. Increasing both Mg and Fe levels led to an increase in the amount of the pi-phase; increasing the iron content led to an increase in the volume fraction of the partially soluble beta- and pi-phases, while Mg2Si particles were completely dissolved. The beta-phase platelets were observed to undergo changes in their morphology due to the

  3. Magnetization Dynamics Through Magnetoimpedance Effect in Isotropic Co2FeAl/Au/Co2FeAl Full-Heusler Alloy Trilayer Films

    NASA Astrophysics Data System (ADS)

    Assolin Corrêa, Marcio; Montardo Escobar, Vivian; Trigueiro-Neto, Osvaldo; Bohn, Felipe; Daiane Sossmeier, Kelly; Gomes Bezerra, Claudionor; Chesman, Carlos; Pearson, John; Hoffmann, Axel

    2013-09-01

    We investigate the magnetization dynamics in low damping parameter α systems by measuring the magnetoimpedance effect over a wide range of frequencies, from 0.1 to 3.0 GHz, in Co2FeAl/Au/Co2FeAl full-Heusler alloy trilayer films grown by magnetron sputtering on glass and MgO substrates. We show that the film produced on the glass substrate presents high magnetoimpedance performance, while that grown on the MgO substrate has low magnetoimpedance performance. Since both films are polycrystalline and have isotropic in-plane magnetic properties, we interpret the magnetoimpedance results in terms of the low damping parameter α and strain effects in the films. Thus, we verified that our films present good magnetoimpedance performance and showed that high performance can be achieved even in films with isotropic in-plane magnetic properties, since they present low damping parameter α.

  4. Observations of Al, Fe and Ca(+) in Mercury's Exosphere

    NASA Technical Reports Server (NTRS)

    Bida, Thomas A.; Killen, Rosemary M.

    2011-01-01

    We report 5-(sigma) tangent column detections of Al and Fe, and strict 3-(sigma) tangent column upper limits for Ca(+) in Mercury's exosphere obtained using the HIRES spectrometer on the Keck I telescope. These are the first direct detections of Al and Fe in Mercury's exosphere. Our Ca(-) observation is consistent with that reported by The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft.

  5. Wettability of AlSi5Mg on Spodumene

    NASA Astrophysics Data System (ADS)

    Fankhänel, Beate; Stelter, Michael; Voigt, Claudia; Aneziris, Christos G.

    2015-02-01

    The development of new filters for the aluminum industry requires investigations on the wettability of aluminum and its alloys on novel filter materials. The requested filter effects require not only an adequate wetting but also information about the interaction between the filter material and the metal. In the present work the wettability of an AlSi5Mg alloy on spodumene (LiAl[Si2O6]) containing substrates is investigated using the sessile drop technique. These measurements were carried out at 1223 K (950 °C) under vacuum. The spodumene-based substrates showed a completely different wetting behavior compared with an alumina substrate. The contact angel reduced more quickly and leveled out at a lower value (75 ± 2 deg) than in case of a pure alumina substrate (90 ± 1 deg). The reason for this behavior is a reaction between the LiAl(Si2O6) and the alloy droplet which supported deoxidation and formed a silica-rich reaction layer at the droplet/substrate interface.

  6. Alloy development and processing of FeAl: An overview

    SciTech Connect

    Maziasz, P.J.; Goodwin, G.M.; Alexander, D.J.; Viswanathan, S.

    1997-03-01

    In the last few years, considerable progress has been made in developing B2-phase FeAl alloys with improved weldability, room-temperature ductility, and high-temperature strength. Controlling the processing-induced microstructure is also important, particularly for minimizing trade-offs in various properties. FeAl alloys have outstanding resistance to high-temperature oxidation, sulfidation, and corrosion in various kinds of molten salts due to formation of protective Al{sub 2}O{sub 3} scales. Recent work shows that FeAl alloys are carburization-resistant as well. Alloys with 36 to 40 at. % Al have the best combination of corrosion resistance and mechanical properties. Minor alloying additions of Mo, Zr, and C, together with microalloying additions of B, produce the best combination of weldability and mechanical behavior. Cast FeAl alloys, with 200 to 400 {mu}m grain size and finely dispersed ZrC, have 2 to 5% tensile ductility in air at room-temperature, and a yield strength > 400 MPa up to about 700 to 750{degrees}C. Extruded ingot metallurgy (I/M) and powder metallurgy (P/M) materials with refined grain sizes ranging from 2 to 50 {mu}m, can have 10 to 15% ductility in air and be much stronger, and can even be quite tough, with Charpy impact energies ranging from 25 to 105 J at room-temperature. This paper highlights progress made in refining the alloy composition and exploring processing effects on FeAl for monolithic applications. It also includes recent progress on developing FeAl weld-overlay technology, and new results on welding of FeAl alloys. It summarizes some of the current industrial testing and interest for applications.

  7. The Relative Strength of the (Fe,Mg)2SiO4 Polymorphs

    NASA Astrophysics Data System (ADS)

    Hunt, S. A.

    2014-12-01

    The polymorphs of (Fe,Mg)2SiO4 (olivine, wadsleyite and ringwoodite) form the major component of the Earth's mantle down to depths of 660 km. Olivine is the stable polymorph to depths of around 410 km, wadsleyite between 410 and 510 km and ringwoodite between 510 and 660 km. The rheology of these three phases plays a significant role in controlling the dynamics of the Earth's mantle and has implications for the origins of deep focus Earthquakes. Each of the three polymorphs has a different crystal structure, along with which comes different physical properties, including rheology. The importance of olivine rheology is reflected in the large body of work investigating it over multiple decades. The rheology of wasleyite and ringwoodite, while equally important, has not been so comprehensively studied because of the historic difficulty of performing controlled strain-rate deformation experiments under the stability conditions of the higher pressure phases. Recent studies investigating the rheology of wadsleyite and ringwoodite [e.g. 1,2] do not directly compare their strengths to that of olivine. To date there is only one study directly comparing the strengths of the (Fe,Mg)2SiO4 polymorphs [3], which demonstrated that at low temperatures (≤800°C) olivine is significantly weaker its higher pressures polymorphs. However, these experiments were stress-relaxation experiments. I will present results of constant strain-rate deformation experiments performed under in-situ conditions, using the newly developed Deformation T-Cup [4]. Because the (Fe,Mg)2SiO4 polymorphs are not stable concurrently, I measure their strength relative to a pyrope garnet standard which is stable within the stability fields of all the polymorphs. The sample of interest and the standard are deformed simultaneously in a single experiment and the ratio of their strains gives the relative strength. References: 1: Hustoft et al., 2012, Earth Planet. Sci. Lett. 361, 7 2: Kawazoe et al., 2010, J. Earth

  8. Fe-Mg-Mn relations of ureilite olivines and pyroxenes and the genesis of ureilites

    NASA Technical Reports Server (NTRS)

    Mittlefehldt, D. W.

    1986-01-01

    Microprobe analyses of ureilite and pigeonite cores are studied. The Fe/Mn-Fe/Mg relationship in the olivine core is examined. It is observed that magnetic processs such as fractional crystallization and partial melting, and FeO reduction contribute to the olivine core composition. The study of the Mg/Mn and Fe/Mn distributions reveals that these two distributions are not in equilibrium in the olivine and pigeonite cores. The effect of a reducing agent, carbon, on the ureilite genesis is investigated. It is concluded that fractional crystallization and FeO reduction are the major processes of ureilite genesis.

  9. Spin Hall magnetoresistance in an ultrathin Co2FeAl system

    NASA Astrophysics Data System (ADS)

    Zhang, Yan-qing; Fu, Hua-rui; Sun, Niu-yi; Che, Wen-ru; Ding, Ding; Qin, Juan; You, Cai-yin; Shan, Rong; Zhu, Zhen-gang

    2016-08-01

    Spin Hall magnetoresistance (SMR) is observed in an ultrathin Co2FeAl layer covered by a thin Pt film. The Co2FeAl layer grown on a MgO substrate should be too thin to be continuous. The result reveals that the magnetic insulator layer, such as yttrium iron garnet (YIG) substrate which is frequently used so far, is actually not a requisite for the observation of SMR. This work may greatly help to understand the true nature of SMR effect.

  10. In situ synchrotron tomographic investigation of the solidification of an AlMg4.7Si8 alloy

    PubMed Central

    Tolnai, D.; Townsend, P.; Requena, G.; Salvo, L.; Lendvai, J.; Degischer, H.P.

    2012-01-01

    The solidification sequence of an AlMg4.7Si8 alloy is imaged in situ by synchrotron microtomography. Tomograms with (1.4 μm)3/voxel have been recorded every minute while cooling the melt from 600 °C at a cooling rate of 5 K min−1 to 540 °C in the solid state. The solidification process starts with the three-dimensional evolution of the α-Al dendritic structure at 590 °C. The growth of the α-Al dendrites is described by curvature parameters that represent the coarsening quantitatively, and ends in droplet-like shapes of the secondary dendrite arms at 577 °C. There, the eutectic valley of α-Al/Mg2Si is reached, forming initially octahedral Mg2Si particles preferentially at the bases of the secondary dendrite arms. The eutectic grows with seaweed-like Mg2Si structures, with increasing connectivity. During this solidification stage Fe-aluminides form and expand as thin objects within the interdendritic liquid. Finally, the remaining liquid freezes as ternary α-Al/Mg2Si/Si eutectic at 558 °C, increasing further the connectivity of the intermetallic phases. The frozen alloy consists of four phases exhibiting morphologies characteristic of their mode of solidification: α-Al dendrites, eutectic α-Al/Mg2Si “Chinese script” with Fe-aluminides, and interpenetrating α-Al/Mg2Si/Si ternary eutectic. PMID:23470958

  11. Fabrication and Spark Plasma Sintering of Magnetic alpha-Fe/MgO Nanocomposite by Mechanical Alloying.

    PubMed

    Lee, Chung-Hyo

    2016-02-01

    Solid-state reduction has occurred during mechanical alloying of a mixture of Fe2O3 and Mg powders at room temperature. It is found that magnetic nanocomposite in which MgO is dispersed in alpha-Fe matrix with nano-sized grains is obtained by mechanical alloying of Fe2O3 with Mg for 30 min. Consolidation of the ball-milled powders was performed in a spark plasma sintering (SPS) machine up to 800-1000 degrees C. X-ray diffraction result shows that the average grain size of alpha-Fe in a-Fe/MgO nanocomposite sintered at 800 degrees C is in the range of 110 nm. It can be also seen that the coercivity of SPS sample sintered at 800 degrees C is still high value of 88 Oe, suggesting that the grain growth of magnetic alpha-Fe phase during SPS process tends to be suppressed. PMID:27433621

  12. XMCD and Magnetic Evidence for Cation Reordering in Synthetic Mg- and Al-substituted Titanomagnetites

    NASA Astrophysics Data System (ADS)

    Lappe, S. C. L. L.; Bowles, J.; Jackson, M.; Keavney, D.

    2014-12-01

    The titanomagnetite (TM) solid solution (Fe3-xTixO4, 0 ≤ x ≤ 1) is one of the most important natural magnetic minerals used in paleomagnetic studies. Natural TMs with Mg- and Al-substitution have recently been shown to have Curie temperatures (TC) that vary strongly with thermal history, and these variations have been indirectly linked to cation reordering in the crystal lattice (Bowles et al. 2013). Here we present the first direct evidence for cation reordering linked to these TC variations. We have synthesized TMs with varying degrees of Mg2+ and Al3+ substitution to better understand the mechanism at work in the natural samples. TC was determined by measuring magnetic susceptibility as function of temperature under Argon atmosphere. Isothermal annealing experiments between 10-1 to 103 h at temperatures between 300-500°C were conducted. Subsequent TC measurements showed that TC on warming increases for longer anneal times and higher anneal temperatures, whereas TC on cooling decreases. These resulting TC changes can be linked to cation ordering within the crystal structure. Splits of the same samples were studied via X-ray magnetic circular dichroism (XMCD), which is sensitive to both Fe valence state and site occupancy. Preliminary results suggest differences in Fe2+/Fe3+ site occupancy for samples of different compositions for different annealing treatments. Using the data collected for these synthetic samples we hope to gain further insight into the complex relationship between thermal history and cation distribution leading to changes in TC. So far, our understanding of the acquisition of thermal remanent magnetization (TRM) in TMs is predicated on the assumption that TC is a constant only depending on the mineral composition. However, the distribution of the magnetic Fe2+ and Fe3+ cations within the crystal lattice has a strong influence on the value of TC and cation (dis-)/ordering processes can result in large changes in TC. In natural samples

  13. Oxidation Resistant Ti-Al-Fe Diffusion Barrier for FeCrAlY Coatings on Titanium Aluminides

    NASA Technical Reports Server (NTRS)

    Brady, Michael P. (Inventor); Smialke, James L. (Inventor); Brindley, William J. (Inventor)

    1996-01-01

    A diffusion barrier to help protect titanium aluminide alloys, including the coated alloys of the TiAl gamma + Ti3Al (alpha2) class, from oxidative attack and interstitial embrittlement at temperatures up to at least 1000 C is disclosed. The coating may comprise FeCrAlX alloys. The diffusion barrier comprises titanium, aluminum, and iron in the following approximate atomic percent: Ti-(50-55)Al-(9-20)Fe. This alloy is also suitable as an oxidative or structural coating for such substrates.

  14. Discovery of New Iron Oxide Fe7O9 and its Solid Solution, (Mg,Fe2+)3Fe3+4O9

    NASA Astrophysics Data System (ADS)

    Sinmyo, R.; Bykova, E.; Ovsyannikov, S. V.; McCammon, C. A.; Kupenko, I.; Ismailova, L.; Dubrovinsky, L. S.

    2015-12-01

    Iron oxides are fundamentally important compounds for Earth science. Particularly, the stability and properties of iron oxides are essential information to understand the structure and chemistry of the mantle. Here we report new high-pressure polymorphs of iron oxide Fe7O9 (Fe3+/Fe2+ = 4/3) and its Fe2+-Mg solid solution (Mg,Fe2+)3Fe3+4O9 that can be recovered at ambient conditions. We synthesized single crystals of the both compounds at about 24-26 GPa using a multi-anvil press. Single crystal X-ray diffraction (XRD) studies showed that the crystal structures of both Fe7O9 and (Mg,Fe2+)3Fe3+4O9 have monoclinic C2/m space groups, that differ from any other known lattices of iron oxides. Mössbauer spectra are in agreement with the crystal structure refined from single crystal XRD. This newly found Fe7O9 polymorph suggests that iron oxides may have more variable mixed valence state under high-pressure condition than previously thought. Based on analogy with Fe2+1+nFe3+2O4+n group, a Fe2+3±nFe3+4O9±n group might be also stable at certain high pressures and temperatures and oxygen fugacity.

  15. Twin Roll Casting of Al-Mg Alloy with High Added Impurity Content

    NASA Astrophysics Data System (ADS)

    Kumar, S.; Hari Babu, N.; Scamans, G. M.; Fan, Z.; O'Reilly, K. A. Q.

    2014-06-01

    The microstructural evolution during twin roll casting (TRC) and downstream processing of AA5754 Al alloy with high added impurity content have been investigated. Strip casts with a high impurity content resulted in coarse α-Al grains and complex secondary phases. The grain size and centerline segregation reduced significantly on the addition of Al-Ti-B grain refiner (GR). Coarse-dendrite arm spacing (DAS) "floating" grains are observed in the impure alloy (IA) with higher volume in the GR strips. Two-dimensional (2D) metallographic analysis of the as-cast strip suggests that secondary phases (Fe-bearing intermetallics and Mg2Si) are discrete and located at the α-Al cell/grain boundaries, while three-dimensional (3D) analysis of extracted particles revealed that they were intact, well interconnected, and located in interdendritic regions. Homogenizing heat treatment of the cast strip breaks the interconnective networks and modifies the secondary phases to a more equiaxed morphology. During rolling, the equiaxed secondary phases align along the rolling direction. X-ray diffraction (XRD) analysis suggests that α-Al(FeMn)Si and Mg2Si are the predominant secondary phases that are formed during casting and remain throughout the downstream processing of the GR-IA. The high-impurity sheet processed from TRC resulted in superior strength and ductility over the sheet processed from small book mold ingot casting. The current study has shown that the TRC process can tolerate higher impurity levels and produce formable sheets from the recycled aluminum for structural applications.

  16. Assimilation Behavior of Calcium Ferrite and Calcium Diferrite with Sintered Al2O3 and MgO

    NASA Astrophysics Data System (ADS)

    Long, Hongming; Wu, Xuejian; Chun, Tiejun; Di, Zhanxia; Yu, Bin

    2016-10-01

    In this study, the assimilation behaviors between calcium ferrite (CF), calcium diferrite (CF2) and sintered Al2O3, and MgO were explored by an improved sessile drop technique, and the interfacial microstructure was discussed. The results indicated that the apparent contact angles of CF slag on Al2O3 and MgO substrate were 15.7 and 5.5 deg, and the apparent contact angles of CF2 slag on Al2O3 and MgO substrate were 17.9 and 7.2 deg, respectively. Namely, CF and CF2 slag were wetting well with Al2O3 and MgO substrate. The dissolution of Al2O3 substrate into the CF and CF2 slag was found to be the driving force of the wetting process. For the CF-MgO and CF2-MgO substrate systems, CaO contrarily distributed with MgO after wetting. For the CF-MgO system, after wetting, the slag was composed of CF and C2F, and most of the Fe2O3 permeated into substrate and formed two permeating layers.

  17. Influence of FeCrAl Content on Microstructure and Bonding Strength of Plasma-Sprayed FeCrAl/Al2O3 Coatings

    NASA Astrophysics Data System (ADS)

    Zhou, Liang; Luo, Fa; Zhou, Wancheng; Zhu, Dongmei

    2016-02-01

    Low-power plasma-sprayed FeCrAl/Al2O3 composite coatings with 1.5 mm thickness have been fabricated for radar absorption applications. The effects of FeCrAl content on the coating properties were studied. The FeCrAl presents in the form of a few thin lamellae and numerous particles, demonstrating relatively even distribution in all the coatings. Results show that the micro-hardness and porosity decrease with the increase in FeCrAl content. With FeCrAl content increasing from 28 to 47 wt.%, the bonding strength of the coatings with 1.5 mm thickness increases from 10.5 to 27 MPa, and the failure modes are composed of cohesive and adhesive failure, which are ascribed to the coating microstructure and the residual stress, respectively.

  18. Incorporation of Ba in Al and Fe pollucite

    NASA Astrophysics Data System (ADS)

    Vance, Eric R.; Gregg, Daniel J.; Griffiths, Grant J.; Gaugliardo, Paul R.; Grant, Charmaine

    2016-09-01

    Ba, the transmutation product of radioactive Cs, can be incorporated at levels of up to ∼0.07 formula units in Cs(1-2x)BaxAlSi2O6 aluminium pollucite formed by sol-gel methods and sintering at 1400 °C, with more Ba forming BaAl2Si2O8 phases. The effect of Ba substitution in pollucite-structured CsFeSi2O6 was also studied and no evidence of Ba substitution in the pollucite structure via cation vacancies or Fe2+ formation was obtained. The Ba entered a Fe-silicate glass structure. Charge compensation was also attempted with a Cs+ + Fe3+ ↔ Ba2+ + Ni2+ scheme but again the Ba formed a glass and NiO was evident. PCT leaching data showed CsFeSi2O6 to be very leach resistant.

  19. Removal of arsenic (V) from water using hierarchical flower-shaped AlOOH/Fe micro/nanostructures

    NASA Astrophysics Data System (ADS)

    Bakina, O. V.; Glazkova, E. A.; Svarovskaya, N. V.; Berenda, A. V.; Lozhkomoev, A. S.; Lerner, M. I.

    2015-10-01

    Hierarchical AlOOH/Fe micro/nanostructures with flower-shaped morphology were fabricated by the reaction of Al/Fe nanoparticles with water. Al/Fe bimetallic nanoparticles have been obtained using the method of simultaneous electrical explosion of metal pairs in a nitrogen atmosphere. The nanoparticles are chemically active and interact with water at 60°C forming the flower-shaped hierarchical pore structures with a high specific surface area. Al/Fe product transformations are presented by the flower-shaped pseudoboehmite surrounded by the lamellar structures enriched with ferric oxides. Flower-shaped AlOOH/Fe micro/nanostructure with flower-shaped morphology is found to serve as an effective adsorbent medium to remove As(V) from water. The adsorption capacity was 43 mg/g (pH = 6.7).

  20. Superhard self-lubricating AlMgB14 films for microelectromechanical devices

    NASA Astrophysics Data System (ADS)

    Tian, Y.; Bastawros, A. F.; Lo, C. C. H.; Constant, A. P.; Russell, A. M.; Cook, B. A.

    2003-10-01

    Performance and reliability of microelectromechanical system (MEMS) components can be enhanced dramatically through the incorporation of protective thin-film coatings. Current-generation MEMS devices prepared by the lithographie-galvanoformung-abformung (LIGA) technique employ transition metals such as Ni, Cu, Fe, or alloys thereof, and hence lack stability in oxidizing, corrosive, and/or high-temperature environments. Fabrication of a superhard self-lubricating coating based on a ternary boride compound AlMgB14 described in this letter has great potential in protective coating technology for LIGA microdevices. Nanoindentation tests show that the hardness of AlMgB14 films prepared by pulsed laser deposition ranges from 45 GPa to 51 GPa, when deposited at room temperature and 573 K, respectively. Extremely low friction coefficients of 0.04-0.05, which are thought to result from a self-lubricating effect, have also been confirmed by nanoscratch tests on the AlMgB14 films. Transmission electron microscopy studies show that the as-deposited films are amorphous, regardless of substrate temperature; however, analysis of Fourier transform infrared spectra suggests that the higher substrate temperature facilitates the formation of the B12 icosahedral framework, therefore leading to the higher hardness.

  1. Bismuth-doped Mg - Al silicate glasses and fibres

    SciTech Connect

    Bufetov, Igor' A; Vel'miskin, V V; Galagan, B I; Denker, B I; Sverchkov, S E; Semjonov, S L; Firstov, Sergei V; Shulman, I L; Dianov, Evgenii M

    2012-09-30

    This paper compares the optical properties of bulk bismuth-doped Mg - Al silicate glasses prepared in an iridium crucible to those of optical fibres prepared by the powder-in-tube method and having a core identical in composition to the glasses. The bulk glasses and fibres are shown to be similar in luminescence properties. The optical loss in the fibres in their IR luminescence band is about one order of magnitude lower than that in the crucible-melted glasses. The level of losses in the fibres and their luminescence properties suggest that such fibres can be made to lase near 1.15 {mu}m. (optical fibres, lasers and amplifiers. properties and applications)

  2. Pulse TIG Welding of Two Al-Mg-Si Alloys

    NASA Astrophysics Data System (ADS)

    Manti, Rajesh; Dwivedi, D. K.; Agarwal, A.

    2008-10-01

    This article reports the influence of pulse tungsten inert gas (TIG) welding parameters on the microstructure, hardness and tensile strength of weld joints of two Al-(0.5-0.8%)Si-(0.5-0.6%)Mg alloy (T4) produced by using three pulse frequencies (25, 33, and 50 Hz) and two duty cycles (40 and 50%). It has been observed that the mechanical properties (hardness and tensile strength) are sensitive to microstructure of weld metal, which is appreciably affected by the pulse parameters. Low frequency produced higher strength and hardness than high pulse frequency under identical welding conditions. Weld metal and HAZ were found stronger than the base metal. SEM study showed that the fracture of weldment was mostly brittle type.

  3. Site occupation, phase stability, crystal and electronic structures of the doped S phase (Al2CuMg)

    NASA Astrophysics Data System (ADS)

    Gu, Jianglong; Gu, Huimin; Zhai, Yuchun; Ma, Peihua

    2016-07-01

    The S phase (Al2CuMg) is an important strengthening phase for the Al-Cu-Mg alloys, which are widely used in the aerospace and transportation industries. The commonly added alloying elements (Mn, Ti, Zr) and the impurity elements (Fe and Si) in the Al-Cu-Mg alloys are always found in the S phase. First-principles calculations based on the density functional theory (DFT) were used to investigate the influence of doping Mn, Ti, Zr, Fe and Si elements on the S phase. Key findings demonstrated that these elements prefer to occupy different atomic sites in the S phase. Ti and Zr improved the structural stability of the S phase. The bulk modulus of the Fe, Si, Ti and Zr doped S phases becomes larger than that of the pure S phase. Both the crystal and electronic structures of the S phase are affected by the dopants. The results of this study provide a better theoretical understanding of the S phase, providing guidance for improved composition design and performance optimization of Al-Cu-Mg alloys.

  4. Cr diffusion in MgAl2O4 synthetic spinels: preliminary results

    NASA Astrophysics Data System (ADS)

    Freda, C.; Celata, B.; Andreozzi, G.; Perinelli, C.; Misiti, V.

    2012-04-01

    Chromian spinel is an accessory phase common in crustal and mantle rocks, including peridotites, gabbros and basalts. Spinel, it has been identified as one of the most effective, sensible, and versatile petrogenetic indicator in mafic and ultramafic rock systems due to the strict interdependence between its physico-chemical properties (chemical composition, cation configuration etc.) and genetic conditions (temperature, pressure, and chemical characteristics of the system). In particular, studies on intra- and inter-crystalline Mg-Fe2+, Cr-Al exchange demonstrated the close relationship between spinel composition and both degree of partial melting and equilibrium temperature of spinel-peridotites. Moreover, studies focused on the chemical zoning of Mg-Fe2+ and/or Cr-Al components in spinel have been used, combined with a diffusion model, to provide quantitative information on peridotites and gabbros pressure-temperature paths and on deformation mechanisms. Although these potentials, most of the experimental studies have been performed on spinels hosting a limited content of divalent iron (sensu stricto, MgAl2O4), whereas the scarce studies on Cr-Al inter-diffusion coefficient have been performed at 3-7 GPa as pressure boundary condition. In order to contribute to the understanding of processes occurring in the lithospheric mantle, we have initiated an experimental research project aiming at determining the Cr-Al inter-diffusion in spinel at 2 GPa pressure and temperature ranging from 1100 to 1250 °C. The experiments were performed in a end-loaded piston cylinder by using a 19 mm assembly and graphite-Pt double capsules. As starting materials we used synthetic Mg-Al spinel (200-300 μm in size) and Cr2O3 powder. Microanalyses of experimental charge were performed on polished carbon-coated mounts by electronic microprobe. Line elemental analyses were made perpendicular to the contact surface between Cr2O3 powder and spinel, at interval of 2 μm. By processing these

  5. Texture and microstructure in co-sputtered Mg-M-O (M = Mg, Al, Cr, Ti, Zr, and Y) films

    NASA Astrophysics Data System (ADS)

    Saraiva, M.; Depla, D.

    2012-05-01

    Mg-M-O solid solution films (M = Mg, Al, Cr, Ti, Zr, and Y) with various M contents are grown employing reactive co-sputtering by varying the target-to-substrate distance. It is shown that all films are biaxially aligned. When the two cathodes are equipped with the same target material (Mg), the in-plane alignment is determined by the cathode closest to the substrate, i.e., by the largest material flux. In the case of nearly equal material fluxes from the two cathodes, double in-plane orientation is observed. This is also the case for the Mg-Al-O and Mg-Cr-O films, while the Mg-Ti-O, Mg-Zr-O and Mg-Y-O films exhibit single in-plane orientation. Pole figures indicate that the grains in Mg-M-O (M different than Mg) are titled; in the Mg-Al-O, Mg-Cr-O, and Mg-Ti-O films, the grains tilt towards the Al, Cr, and Ti metal flux, respectively, while the grain tilt of the Mg-Zr-O and Mg-Y-O films is found to be towards the Mg metal flux. Furthermore, SEM cross-sectional images of the Mg-M-O films reveal columnar microstructure with columns tilted to the same direction as the grains. A mechanism which is based on the cation radius change upon the incorporation of an M atom in the MgO lattice is proposed to explain the tilting.

  6. Large tunneling magnetoresistance effect at high voltage drop for Co-based Heusler alloy/MgO/CoFe junctions

    SciTech Connect

    Rata, A. D.; Braak, H.; Buergler, D. E.; Schneider, C. M.

    2007-05-01

    Growth and magnetic characterization of thin films of Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al and Co{sub 2}MnSi full-Heusler compounds are investigated. Thin films were deposited by magnetron sputtering at room temperature directly onto oxidized Si wafers. These Heusler films are magnetically very soft and ferromagnetic with Curie temperatures well above room temperature. Polycrystalline Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al Heusler films combined with MgO barriers and CoFe counter electrodes are structured to magnetic tunnel junctions and yield almost 50% magnetoresistance at room temperature. The magnetoresistance shows a strong bias dependence with the maximum occurring at a voltage drop well above 1 V. This special feature is accompanied by only a moderate temperature dependence of the tunnel magnetoresistance.

  7. Recyclable Mg-Al layered double hydroxides for fluoride removal: Kinetic and equilibrium studies.

    PubMed

    Kameda, Tomohito; Oba, Jumpei; Yoshioka, Toshiaki

    2015-12-30

    Mg-Al layered double hydroxides (LDHs) intercalated with NO3(-) (NO3 · Mg-Al LDH) and Cl(-) (Cl · Mg-Al LDH) were found to adsorb fluoride from aqueous solutions. Fluoride is removed by anion exchange in solution with NO3(-) and Cl(-) intercalated in the LDH interlayer. In both cases, the residual F concentration is lower than the effluent standards for F in Japan (8 mg/L). The rate-determining step in the removal of F using NO3 · Mg-Al and Cl · Mg-Al LDH is chemical adsorption involving F(-) anion exchange with intercalated NO3(-) and Cl(-) ions. The removal of F is described by pseudo-second-order reaction kinetics, with Langmuir-type adsorption. The values obtained for the maximum adsorption and the equilibrium adsorption constant are respectively 3.3 mmol g(-1) and 2.8 with NO3 · Mg-Al LDH, and 3.2 mmol g(-1) and 1.5 with Cl · Mg-Al LDH. The F in the F · Mg-Al LDH produced in these reactions was found to exchange with NO3(-) and Cl(-) ions in solution. The regenerated NO3 · Mg-Al and Cl · Mg-Al LDHs thus obtained can be used once more to capture aqueous F. This suggests that NO3 · Mg-Al and Cl · Mg-Al LDHs can be recycled and used repeatedly for F removal.

  8. Melting relations in the system FeCO3-MgCO3 and thermodynamic modelling of Fe-Mg carbonate melts

    NASA Astrophysics Data System (ADS)

    Kang, Nathan; Schmidt, Max W.; Poli, Stefano; Connolly, James A. D.; Franzolin, Ettore

    2016-09-01

    To constrain the thermodynamics and melting relations of the siderite-magnesite (FeCO3-MgCO3) system, 27 piston cylinder experiments were conducted at 3.5 GPa and 1170-1575 °C. Fe-rich compositions were also investigated with 13 multi-anvil experiments at 10, 13.6 and 20 GPa, 1500-1890 °C. At 3.5 GPa, the solid solution siderite-magnesite coexists with melt over a compositional range of X Mg (=Mg/(Mg + Fetot)) = 0.38-1.0, while at ≥10 GPa solid solution appears to be complete. At 3.5 GPa, the system is pseudo-binary because of the limited stability of siderite or liquid FeCO3, Fe-rich carbonates decomposing at subsolidus conditions to magnetite-magnesioferrite solid solution, graphite and CO2. Similar reactions also occur with liquid FeCO3 resulting in melt species with ferric iron components, but the decomposition of the liquid decreases in importance with pressure. At 3.5 GPa, the metastable melting temperature of pure siderite is located at 1264 °C, whereas pure magnesite melts at 1629 °C. The melting loop is non-ideal on the Fe side where the dissociation reaction resulting in Fe3+ in the melt depresses melting temperatures and causes a minimum. Over the pressure range of 3.5-20 GPa, this minimum is 20-35 °C lower than the (metastable) siderite melting temperature. By merging all present and previous experimental data, standard state (298.15 K, 1 bar) thermodynamic properties of the magnesite melt (MgCO3L) end member are calculated and the properties of (Fe,Mg)CO3 melt fit by a regular solution model with an interaction parameter of -7600 J/mol. The solution model reproduces the asymmetric melting loop and predicts the thermal minimum at 1240 °C near the siderite side at X Mg = 0.2 (3.5 GPa). The solution model is applicable to pressures reaching to the bottom of the upper mantle and allows calculation of phase relations in the FeO-MgO-O2-C system.

  9. Unravelling regolith material types using Mg/Al and K/Al plot to support field regolith identification in the savannah regions of NW Ghana, West Africa

    NASA Astrophysics Data System (ADS)

    Arhin, Emmanuel; Zango, Saeed M.

    2015-12-01

    The XRF analytical method was used to measure the weight % of the major oxides in regolith samples. The metal weight % of Mg, K and Al were calculated from their oxides and were normalised relative to immobile Al calculated from its oxide. The plot of Mg/Al and K/Al identified the regolith of the study area to consist of 137 transported clays, 4 ferruginous sediments or ferricrete, 2 lateritic duricrust and 4 saprolites. Surface regolith that had undergone secondary transformation and shows compositional overlaps were 4 transported clays with Fe-oxide impregnation may be referred to as nodular laterite and 5 ferruginous saprolites. The variable regolith materials features identified from the 154 samples enabled the characterisation and identification of the different sample materials because an overprint of bedrock geochemistry is reflected in the regolith. Plot of Mg/Al and K/Al highlighted the compositional variability of the regolith samples and refute the notion of the homogeneity of all the sampled materials in the area. The study thus recognized Mg/Al versus K/Al plots to be used in supporting field identification of regolith mapping units particularly in complex regolith terrains of savannah regions of Ghana and in similar areas where geochemical exploration surveys are being carried out under cover.

  10. Atomic origin of the spin-polarization of the Co2FeAl Heusler compound

    NASA Astrophysics Data System (ADS)

    Liang, Jaw-Yeu; Lam, Tu-Ngoc; Lin, Yan-Cheng; Chang, Shu-Jui; Lin, Hong-Ji; Tseng, Yuan-Chieh

    2016-02-01

    Using synchrotron x-ray techniques, we studied the Co2FeAl spin-polarization state that generates the half-metallicity of the compound during an A2 (low-spin)  →  B2 (high-spin) phase transition. Given the advantage of element specificity of x-ray techniques, we could fingerprint the structural and magnetic cross-reactions between Co and Fe within a complex Co2FeAl structure deposited on a MgO (0 0 1) substrate. X-ray diffraction and extended x-ray absorption fine structure investigations determined that the Co atoms preferably populate the (1/4,1/4,1/4) and (3/4,3/4,3/4) sites during the development of the B2 phase. X-ray magnetic spectroscopy showed that although the two magnetic elements were ferromagnetically coupled, they interacted in a competing manner via a charge-transfer effect, which enhanced Co spin polarization at the expense of Fe spin polarization during the phase transition. This means that the spin-polarization of Co2FeAl was electronically dominated by Fe in A2 whereas the charge transfer turned the dominance to Co upon B2 formation. Helicity-dependent x-ray absorption spectra also revealed that only the minority state of Co/Fe was involved in the charge-transfer effect whereas the majority state was independent of it. Despite an overall increase of Co2FeAl magnetization, the charge-transfer effect created an undesired trade-off during the Co-Fe exchange interactions, because of the presence of twice as many X sites (Co) as Y sites (Fe) in the Heusler X 2 YZ formula. This suggests that the spin-polarization of Co2FeAl is unfortunately regulated by compromising the enhanced X (Co) sites and the suppressed Y (Fe) sites, irrespective of the development of the previously known high-spin-polarization phase of B2. This finding provides a possible cause for the limited half-metallicity of Co2FeAl discovered recently. Electronic tuning between the X and Y sites is necessary to further increase the spin-polarization, and likely the half

  11. Effect of reaction time and (Ca+Mg)/Al molar ratios on crystallinity of Ca-Mg-Al layered double Hydroxide

    NASA Astrophysics Data System (ADS)

    Heraldy, E.; Nugrahaningtyas, K. D.; Sanjaya, F. B.; Darojat, A. A.; Handayani, D. S.; Hidayat, Y.

    2016-02-01

    Ca-Mg-Al Layered Double Hydroxides (Ca-Mg-Al-LDH) compounds were successfully synthesized from brine water and AlCl3.6H2O as the starting materials by coprecipitation method. The product result was characterized by X-ray powder diffraction (XRD) and Fourier transform infrared (FT-IR). The effects of the reaction time and the molar ratios of the raw material on the crystallinity of Ca-Mg-Al-LDH were examining. Results show that increasing reaction time (30; 60 and 90 min.) could improve the crystallinity and monodispersity of layered double hydroxide compounds particles. The well-defined Ca-Mg- Al-LDH could be prepared with (Ca+Mg)/Al molar ratios 0.5.

  12. Effects of post-growth annealing in a CoFeB/MgO/CoFeB trilayer structure

    NASA Astrophysics Data System (ADS)

    Ying, Ji-Feng; Ter Lim, Sze; Tran, Michael; Ji, Rong

    2015-11-01

    CoFeB/MgO/CoFeB tri-layer thin-film stacks have been widely used in the design of STT-RAM devices as functional magnetic-tunnel-junction (MTJ) structures. The materials properties of the CoFeB and MgO layers, including composition and lattice quality, have been extensively researched from the stand point of optimizing for the best MTJ performance. On the other hand, post-growth annealing is required for the MTJ structure to acquire its functional property, i.e. its TMR performance. In this work, we have studied the various possible effects resulting from the post-growth annealing process. Specifically, we show that the post-growth annealing causes boron in the top and bottom CoFeB layers to migrate into the adjacent Ta layers as well as deterioration in lattice quality of the MgO layer. Furthermore, we evaluate other effects that could be possibly induced during the annealing process, including Ta diffusion and layer intermixing in the CoFeB/MgO/CoFeB tri-layer structure. The post-growth annealing causes little change in the Ta diffusion and the layer intermixing. These annealing effects were also evaluated with respect to variations in the MgO growth process; more specifically, an additional natural oxidation treatment during the MgO layer deposition and the insertion of a Fe layer before the MgO layer. Our results indicate that the addition of a natural oxidation process during the MgO deposition process and the insertion of a thin-layer of Fe before the MgO layer both lead to a reduction in the layer intermixing between the MgO and the CoFeB layer and to an improvement in MgO lattice quality. We also show that the post-growth annealing does not alter the beneficial effect of these MgO growth process modifications.

  13. Cytotoxic, Genotoxic, and Neurotoxic Effects of Mg, Pb, and Fe on Pheochromocytoma (PC-12) Cells

    PubMed Central

    Sanders, Talia; Liu, Yi-Ming; Tchounwou, Paul B.

    2014-01-01

    Metals such as lead (Pb), magnesium (Mg), and iron (Fe) are ubiquitous in the environment as a result of natural occurrence and anthropogenic activities. Although Mg, Fe and others are considered essential elements, high level of exposure has been associated with severe adverse health effects including cardiovascular, hematological, nephrotoxic, hepatotoxic, and neurologic abnormalities in humans. In the present study we hypothesized that Mg, Pb, and Fe are cytotoxic, genotoxic and neurotoxic, and their toxicity is mediated through oxidative stress and alteration in protein expression. To test the hypothesis, we used the pheochromocytoma (PC-12) cell line as a neuro cell model and performed the LDH assay for cell viability, Comet assay for DNA damage, Western blot for oxidative stress, and HPLC-MS to assess the concentration levels of neurological biomarkers such as glutamate, dopamine (DA), and 3-methoxytyramine (3-MT). The results of this study clearly show that Mg, Pb, and Fe, respectively in the form of MgSO4, Pb(NO3)2, FeCl2, and FeCl3 induce cytotoxicity, oxidative stress, and genotoxicity in PC-12 cells. In addition, exposure to these metallic compounds caused significant changes in the concentration levels of glutamate, dopamine, and 3-MT in PC-12 cells. Taken together the findings suggest that MgSO4, Pb(NO3)2, FeCl2, and FeCl3 have the potential to induce substantial toxicity to PC-12 cells. PMID:24942330

  14. Thermodynamic Phase Relations in the MgO-FeO-SiO2 System in the Lower Mantle

    NASA Astrophysics Data System (ADS)

    Wolf, A. S.; Caracas, R.; Asimow, P. D.

    2008-12-01

    The perovskite (Pv) to post-perovskite (PPv) phase transition at pressures near the Earth's core-mantle boundary (CMB) is currently the favored candidate for explaining most, if not all, of the peculiarities of the D" layer (~200 km region above core) [1, 2]. Additionally, the pressure- and temperature-dependence of this phase boundary in the Earth provides the possibility of an important new thermo-barometer at the bottom of the convecting mantle. The post-perovskite phase boundary in pure MgSiO3 is fairly well known, but the experimental and calculated results on the partitioning of Fe among the stable coexisting phases and its influence on the transition pressure are currently contradictory [3, 4, 5, 6]. Using density functional theory (DFT), we investigate the MgO-FeO-SiO2 ternary system over the temperatures and pressures relevant to the core-mantle boundary. We use DFT to calculate the energies of the relevant stable phases (Pv, PPv, (Mg,Fe)O magnesio-wustite, and SiO2 stishovite) for a range of Fe compositions along the Mg-Fe binary. These results are fit with a Vinet equation of state, allowing us to parameterize the effect of both pressure and Fe composition. The effect of temperature is modeled using a Grüneisen thermal correction, where the vibrational heat capacities are determined using DFT perturbation calculations and the quasi-harmonic approximation. These pressure-, temperature-, and composition-dependent equations of state are then used to explore the predicted phase relations. The results of this investigation are a complete thermodynamic description of the stable phases for this simplified chemistry and a theoretical prediction for iron partioning in the lower mantle. In particular, we find that there may be a coincidence point (azeotrope) on the Pv-PPv phase loop, across which the sense of Fe-partitioning changes sign, as well as significant immiscibility between Mg-rich and Fe-rich post-perovskite. These findings help explain many of the

  15. A combined computational and experimental investigation of Mg doped α-Fe2O3.

    PubMed

    Kosa, Monica; Barad, Hannah Noa; Singh, Vijay; Keller, David A; Shimanovich, Klimentiy; Rühle, Sven; Anderson, Assaf Y; Zaban, Arie; Major, Dan Thomas

    2016-01-14

    In the current work, pristine α-Fe2O3 metal oxide was doped with Mg in an attempt to modulate its electronic properties. To this end, we employed an experimental high throughput strategy, including scanning XRD and optical spectroscopy, which were complimented by atomistic density functional theory (DFT) calculations. The combined study reveals that at Mg/Fe atomic ratios up to ∼1/3, the bandgaps of the hematite-Mg composite materials are similar to that of the pure material. The observed bandgaps are rationalized by electronic band structure and density of states calculations. Additional rationale for the similar bandgaps in pure and doped hematite is provided by topological Bader charge analyses, which indicate that the Mg and Fe ions in the hematite matrix have similar partial atomic charges. Nonetheless, the small charge density difference between the Mg and Fe ions induces a slight spin polarization on both oxygen and Fe ions, resulting in changes in the band edges. Further charge density analyses, using charge density maps and chemical-bonding analyses with the crystal orbital Hamiltonian population scheme, indicate that Mg forms ionic bonds with the neighboring oxygen atoms. This change from iron-oxygen covalent bonds to a more ionic nature for magnesium-oxygen bonds is probably responsible for the reduction observed in the computed bulk modulus of α-Mg(0.17)Fe(1.83)O3 (193 GPa) compared to α-Fe2O3 (202 GPa). PMID:26625981

  16. A combined computational and experimental investigation of Mg doped α-Fe2O3.

    PubMed

    Kosa, Monica; Barad, Hannah Noa; Singh, Vijay; Keller, David A; Shimanovich, Klimentiy; Rühle, Sven; Anderson, Assaf Y; Zaban, Arie; Major, Dan Thomas

    2016-01-14

    In the current work, pristine α-Fe2O3 metal oxide was doped with Mg in an attempt to modulate its electronic properties. To this end, we employed an experimental high throughput strategy, including scanning XRD and optical spectroscopy, which were complimented by atomistic density functional theory (DFT) calculations. The combined study reveals that at Mg/Fe atomic ratios up to ∼1/3, the bandgaps of the hematite-Mg composite materials are similar to that of the pure material. The observed bandgaps are rationalized by electronic band structure and density of states calculations. Additional rationale for the similar bandgaps in pure and doped hematite is provided by topological Bader charge analyses, which indicate that the Mg and Fe ions in the hematite matrix have similar partial atomic charges. Nonetheless, the small charge density difference between the Mg and Fe ions induces a slight spin polarization on both oxygen and Fe ions, resulting in changes in the band edges. Further charge density analyses, using charge density maps and chemical-bonding analyses with the crystal orbital Hamiltonian population scheme, indicate that Mg forms ionic bonds with the neighboring oxygen atoms. This change from iron-oxygen covalent bonds to a more ionic nature for magnesium-oxygen bonds is probably responsible for the reduction observed in the computed bulk modulus of α-Mg(0.17)Fe(1.83)O3 (193 GPa) compared to α-Fe2O3 (202 GPa).

  17. FE and MG Isotopic Analyses of Isotopically Unusual Presolar Silicate Grains

    NASA Technical Reports Server (NTRS)

    Nguyen, A. N.; Messenger, S.; Ito, M.; Rahman, Z.

    2011-01-01

    Interstellar and circumstellar silicate grains are thought to be Mg-rich and Fe-poor, based on astronomical observations and equilibrium condensation models of silicate dust formation in stellar outflows. On the other hand, presolar silicates isolated from meteorites have surprisingly high Fe contents and few Mg-rich grains are observed. The high Fe contents in meteoritic presolar silicates may indicate they formed by a non-equilibrium condensation process. Alternatively, the Fe in the stardust grains could have been acquired during parent body alteration. The origin of Fe in presolar silicates may be deduced from its isotopic composition. Thus far, Fe isotopic measurements of presolar silicates are limited to the Fe-54/Fe-56 ratios of 14 grains. Only two slight anomalies (albeit solar within error) were observed. However, these measurements suffered from contamination of Fe from the adjacent meteorite matrix, which diluted any isotopic anomalies. We have isolated four presolar silicates having unusual O isotopic compositions by focused ion beam (FIB) milling and obtained their undiluted Mg and Fe isotopic compositions. These compositions help to identify the grains stellar sources and to determine the source of Fe in the grains.

  18. Iron spin state and site distribution in FeAlO3-bearing bridgmanite

    NASA Astrophysics Data System (ADS)

    Mohn, Chris E.; Trønnes, Reidar G.

    2016-04-01

    DFT at the GGA, GGA + U and hybrid functional levels were used to investigate thousands of different Al and Fe3+ configurations of MgSiO3-FeAlO3 (MS-FA) and MgSiO3-FeAlO3-Al2O3 bridgmanite at deep mantle conditions. Comparison of the different functionals and atomic charge analysis suggests that GGA, frequently used to explain high to low spin transitions observed in several Mössbauer and X-ray emission spectroscopy experiments, is hampered by spurious self-interaction errors in the exchange-correlation energy. Configurational Boltzmann averaging shows that the B site is thermally inaccessible to Fe3+ at the GGA + U and hybrid levels, and we find no evidence for a spin-pairing transition in fully (thermodynamically) equilibrated samples of bridgmanite, even at the lowermost mantle conditions. The comparison of the cation radii of Fe3+ and Mg supports a spin transition accompanied by a site exchange, but the flexibility of Fesbnd O bonds to locally adapt promotes the incorporation of iron in the irregularly coordinated A-site. The concept of ionic radii is therefore unsuitable for analysis of spin state and site exchange in bridgmanite at these conditions. Consistent with previous computational work and experimental studies with glass and gel as starting material, we find that ferric iron kinetically trapped at the B site undergoes a spin transition under lowermost mantle conditions. In bridgmanite with mole fraction of Fe3+ >Al a charge-balancing amount of low spin Fe3+ will be thermodynamically stable at the B site, but because bridgmanite in peridotitic and basaltic lithologies mostly has Al/Fetotal above unity, FA with high spin Fe3+ in the A-site will be the dominant iron component. The lack of a Fe3+ spin transition in the FA-component has important implications for bridgmanite-ferropericlase partitioning of iron and magnesium and the mineral physics of the lowermost mantle.

  19. Nanoscale environments associated with bioweathering of a Mg-Fe-pyroxene

    PubMed Central

    Benzerara, Karim; Yoon, Tae Hyun; Menguy, Nicolas; Tyliszczak, Tolek; Brown, Gordon E.

    2005-01-01

    Microorganisms are believed to create microenvironments leading to reaction products not predictable from equilibrium thermodynamics and to unique biomineral morphologies. Unambiguous evidence for such environments is, however, rare in natural samples. We have used scanning transmission x-ray microscopy and spectromicroscopy at the sub-40-nm scale, coupled with transmission electron microscopy, to examine bioweathering products on a meteoritic Fe-Mg-orthopyroxene colonized by a filamentous microorganism. Our measurements reveal an amorphous Al-rich layer beneath the microorganism, calcium carbonates of unique morphology intimately associated with polysaccharides adjacent to the microorganism, and regions surrounding the microorganism with different iron oxidation states. Our results confirm the presence of different microenvironments at this microorganism–mineral interface and provide unique nanometer-scale views of microbially controlled pyroxene weathering products. PMID:15647362

  20. Radiation damage in MgAl2O4

    NASA Astrophysics Data System (ADS)

    Summers, G. P.; White, G. S.; Lee, K. H.; Crawford, J. H., Jr.

    1980-03-01

    Exposure of single crystals of MgAl2O4 to fast neutrons and to Van de Graaff electrons with energies in excess of 0.35 MeV introduces an optical-absorption band at 5.3 eV with a 1-eV half-width. This band can be partially bleached at temperatures as low as 40 K and a shoulder at 4.75 eV develops concurrently. This bleaching treatment also partially destroys a previously reported V-type absorption centered at 3.2 eV. Subsequent exposure to ionizing radiation destroys the 4.75-eV band and restores both the 5.3- and 3.2-eV bands to their original intensities. Since this behavior is analogous to the interconversion of F to F+ centers in Al2O3, it is concluded that the 5.3-eV band is the principal optical transition of the F center (two electrons trapped at an oxide-ion vacancy) and the 4.75-eV band is attributed to absorption by the F+ center (one electron trapped at an oxide-ion vacancy). In electron-irradiated crystals the 5.3-eV absorption begins to anneal near 110°C and is about 90% destroyed upon isochronal annealing (10-min pulses) up to 355°C. Neutron-irradiated crystals behave similarly. Measurement of the threshold energy for damage by electrons at 77 K yields a displacement energy for the creation of O2- interstitial-vacancy pairs of 59 eV. The defect yield drops off substantially with increasing temperature, and at room temperature the apparent O2- displacement energy is 130 eV. Possible reasons for this strong temperature effect are discussed.

  1. The effect of Mg location on Co-Mg-Ru/γ-Al2O3 Fischer–Tropsch catalysts

    PubMed Central

    Combes, Gary B.; Ozkaya, Don; Enache, Dan I.; Ellis, Peter R.; Kelly, Gordon; Rosseinsky, Matthew J.

    2016-01-01

    The effectiveness of Mg as a promoter of Co-Ru/γ-Al2O3 Fischer–Tropsch catalysts depends on how and when the Mg is added. When the Mg is impregnated into the support before the Co and Ru addition, some Mg is incorporated into the support in the form of MgxAl2O3+x if the material is calcined at 550°C or 800°C after the impregnation, while the remainder is present as amorphous MgO/MgCO3 phases. After subsequent Co-Ru impregnation MgxCo3−xO4 is formed which decomposes on reduction, leading to Co(0) particles intimately mixed with Mg, as shown by high-resolution transmission electron microscopy. The process of impregnating Co into an Mg-modified support results in dissolution of the amorphous Mg, and it is this Mg which is then incorporated into MgxCo3−xO4. Acid washing or higher temperature calcination after Mg impregnation can remove most of this amorphous Mg, resulting in lower values of x in MgxCo3−xO4. Catalytic testing of these materials reveals that Mg incorporation into the Co oxide phase is severely detrimental to the site-time yield, while Mg incorporation into the support may provide some enhancement of activity at high temperature. PMID:26755760

  2. The Electrochemical Co-reduction of Mg-Al-Y Alloys in the LiCl-NaCl-MgCl2-AlF3-YCl3 Melts

    NASA Astrophysics Data System (ADS)

    Li, Mei; Liu, Yaochen; Han, Wei; Wang, Shanshan; Zhang, Milin; Yan, Yongde; Shi, Weiqun

    2015-04-01

    The electrochemical formation of Mg-Al-Y alloys was studied in the LiCl-NaCl-MgCl2 melts by the addition of AlF3 and YCl3 on a molybdenum electrode at 973 K (700 °C). In order to reduce the volatilization of salt solvent in the electrolysis process, the volatile loss of LiCl-NaCl-MgCl2 and LiCl-KCl-MgCl2 melts was first measured in the temperature range from 873 K to 1023 K (600 °C to 750 °C). Then, the electrochemical behaviors of Mg(II), Al(III), Y(III) ions and alloy formation processes were investigated by cyclic voltammetry, chronopotentiometry, and open circuit chronopotentiometry. The cyclic voltammograms indicate that the under-potential deposition of magnesium and yttrium on pre-deposited Al leads to formation of Mg-Al and Al-Y intermetallic compounds. The Mg-Al-Y alloys were prepared by galvanostatic electrolysis in the LiCl-NaCl-MgCl2-AlF3-YCl3 melts and characterized by X-ray diffraction and scanning electron microscopy with energy dispersive spectrometry. Composition of the alloys was analyzed by inductively coupled plasma-atomic emission spectrometer, and current efficiency was also determined by the alloy composition.

  3. Host Atom Diffusion in Ternary Fe-Cr-Al Alloys

    NASA Astrophysics Data System (ADS)

    Rohrberg, Diana; Spitzer, Karl-Heinz; Dörrer, Lars; Kulińska, Anna J.; Borchardt, Günter; Fraczkiewicz, Anna; Markus, Torsten; Jacobs, Michael H. G.; Schmid-Fetzer, Rainer

    2014-01-01

    In the Fe-rich corner of the Fe-Cr-Al ternary phase diagram, both interdiffusion experiments [1048 K to 1573 K (775 °C to 1300 °C)] and 58Fe tracer diffusion experiments [873 K to 1123 K (600 °C to 850 °C)] were performed along the Fe50Cr50-Fe50Al50 section. For the evaluation of the interdiffusion data, a theoretical model was used which directly yields the individual self-diffusion coefficients of the three constituents and the shift of the original interface of the diffusion couple through inverse modeling. The driving chemical potential gradients were derived using a phenomenological Gibbs energy function which was based on thoroughly assessed thermodynamic data. From the comparison of the individual self-diffusivities of Fe as obtained from interdiffusion profiles and independent 58Fe tracer diffusivities, the influence of the B2-A2 order-disorder transition becomes obvious, resulting in a slightly higher activation enthalpy for the bcc-B2 phase and a significantly lower activation entropy for this phase.

  4. Weldability of Fe3Al based iron aluminide alloys

    NASA Astrophysics Data System (ADS)

    Zacharia, T.; Maziasz, P. J.; David, S. A.; McKamey, C. G.

    An investigation was carried out to determine the weldability of Fe3Al type alloys. Sigmajig tests of a commercial heat of FA-129 alloy indicate that hot-cracking may not be a problem for this alloy. Additionally, several new Fe3Al based iron aluminides were evaluated for weldability. The preliminary results are encouraging and suggest that some of these alloys have comparable or better weldability than FA-129 based iron-aluminides. For the first time, successful welds, without hot or cold cracking, were made on 13 mm (0.5 in.) thick plates from a commercial heat of FA-129 using the proper choice of welding conditions and parameters.

  5. Al-doped MgB2 materials studied using electron paramagnetic resonance and Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Bateni, Ali; Erdem, Emre; Repp, Sergej; Weber, Stefan; Somer, Mehmet

    2016-05-01

    Undoped and aluminum (Al) doped magnesium diboride (MgB2) samples were synthesized using a high-temperature solid-state synthesis method. The microscopic defect structures of Al-doped MgB2 samples were systematically investigated using X-ray powder diffraction, Raman spectroscopy, and electron paramagnetic resonance. It was found that Mg-vacancies are responsible for defect-induced peculiarities in MgB2. Above a certain level of Al doping, enhanced conductive properties of MgB2 disappear due to filling of vacancies or trapping of Al in Mg-related vacancy sites.

  6. Laser cladding of a Mg based Mg-Gd-Y-Zr alloy with Al-Si powders

    NASA Astrophysics Data System (ADS)

    Chen, Erlei; Zhang, Kemin; Zou, Jianxin

    2016-03-01

    In the present work, a Mg based Mg-Gd-Y-Zr alloy was subjected to laser cladding with Al-Si powders at different laser scanning speeds in order to improve its surface properties. It is observed that the laser clad layer mainly contains Mg2Si, Mg17Al12 and Al2(Gd,Y) phases distributed in the Mg matrix. The depth of the laser clad layer increases with decreasing the scanning speed. The clad layer has graded microstructures and compositions. Both the volume fraction and size of Mg2Si, Mg17Al12 and Al2(Gd,Y) phases decreases with the increasing depth. Due to the formation of these hardening phases, the hardness of clad layer reached a maximum value of HV440 when the laser scanning speed is 2 mm/s, more than 5 times of the substrate (HV75). Besides, the corrosion properties of the untreated and laser treated samples were all measured in a NaCl (3.5 wt.%) aqueous solution. The corrosion potential was increased from -1.77 V for the untreated alloy to -1.13 V for the laser clad alloy with scanning rate of 2 mm/s, while the corrosion current density was reduced from 2.10 × 10-5 A cm-2 to 1.64 × 10-6 A cm-2. The results show that laser cladding is an efficient method to improve surface properties of Mg-Rare earth alloys.

  7. Multicomponent diffusion in garnets I: general theoretical considerations and experimental data for Fe-Mg systems

    NASA Astrophysics Data System (ADS)

    Borinski, Sascha André; Hoppe, Ulrich; Chakraborty, Sumit; Ganguly, Jibamitra; Bhowmik, Santanu Kumar

    2012-10-01

    We have carried out a combined theoretical and experimental study of multicomponent diffusion in garnets to address some unresolved issues and to better constrain the diffusion behavior of Fe and Mg in almandine-pyrope-rich garnets. We have (1) improved the convolution correction of concentration profiles measured using electron microprobes, (2) studied the effect of thermodynamic non-ideality on diffusion and (3) explored the use of a mathematical error minimization routine (the Nelder-Mead downhill simplex method) compared to the visual fitting of concentration profiles used in earlier studies. We conclude that incorporation of thermodynamic non-ideality alters the shapes of calculated profiles, resulting in better fits to measured shapes, but retrieved diffusion coefficients do not differ from those retrieved using ideal models by more than a factor of 1.2 for most natural garnet compositions. Diffusion coefficients retrieved using the two kinds of models differ only significantly for some unusual Mg-Mn-Ca-rich garnets. We found that when one of the diffusion coefficients becomes much faster or slower than the rest, or when the diffusion couple has a composition that is dominated by one component (>75 %), then profile shapes become insensitive to one or more tracer diffusion coefficients. Visual fitting and numerical fitting using the Nelder-Mead algorithm give identical results for idealized profile shapes, but for data with strong analytical noise or asymmetric profile shapes, visual fitting returns values closer to the known inputs. Finally, we have carried out four additional diffusion couple experiments (25-35 kbar, 1,260-1,400 °C) in a piston-cylinder apparatus using natural pyrope- and almandine-rich garnets. We have combined our results with a reanalysis of the profiles from Ganguly et al. (1998) using the tools developed in this work to obtain the following Arrhenius parameters in D = D 0 exp{-[ Q 1bar + ( P-1)Δ V +]/ RT} for D {Mg/*} and D {Fe/*}: Mg

  8. On the entropy of glaucophane Na2Mg3Al2Si8O22(OH)2

    USGS Publications Warehouse

    Robie, R.A.; Hemingway, B.S.; Gillet, P.; Reynard, B.

    1991-01-01

    The heat capacity of glaucophane from the Sesia-Lanza region of Italy having the approximate composition (Na1.93Ca0.05Fe0.02) (Mg2.60Fe0.41) (Al1.83Fe0.15Cr0.01) (Si7.92Al0.08)O22(OH)2 was measured by adiabatic calorimetry between 4.6 and 359.4 K. After correcting the Cp0data to values for ideal glaucophane, Na2Mg3Al2Si8O22(OH)2 the third-law entropy S2980-S00was calculated to be 541.2??3.0 J??mol-1??K-1. Our value for S2980-S00is 12.0 J??mol-1??K-1 (2.2%) smaller than the value of Likhoydov et al. (1982), 553.2??3.0, is within 6.2 J??mol-1??K-1 of the value estimated by Holland (1988), and agrees remarkably well with the value calculated by Gillet et al. (1989) from spectroscopic data, 539 J??mol-1??K-1. ?? 1991 Springer-Verlag.

  9. The Formation of Fe/Mg Smectite Under Mildly Acidic Conditions on Early Mars

    NASA Technical Reports Server (NTRS)

    Sutter, B.; Golden, D. C.; Ming, Douglas W.; Niles, P. B.

    2011-01-01

    The detection of Fe/Mg smectites and carbonate in Noachian and early Hesperian terrain of Mars suggests that neutral to mildly alkaline conditions prevailed during the early history of Mars. If early Mars surface geochemical conditions were neutral to moderately alkaline with a denser CO2 atmosphere than today, then large carbonates deposits should be more widely detected in Noachian terrain. Why have so few carbonate deposits been detected compared to Fe/Mg smectites? Fe/Mg smectites on early Mars formed under mildly acidic conditions, which would preclude the extensive formation of carbonate deposits. The goal of the proposed work is to evaluate the formation of Fe/Mg smectites under mildly acidic conditions.

  10. Aluminum and silicon diffusion in Fe-Cr-Al alloys

    SciTech Connect

    Heesemann, A.; Schmidtke, E.; Faupel, F.; Kolb-Telieps, A.; Kloewer, J.

    1999-02-05

    Foils of Fe-Cr-Al alloys containing about 20 wt% Cr, 5 wt% Al and additions of Si and reactive elements like Ce, La, Y, Hf, Zr or Ti are widely used as a substrate in metal-supported automotive catalytic converters. In the present paper the authors report on measurements of Al and Si diffusion in Fe-Cr-Al alloys. Due to a lack of suitable radiotracers concentration profiles were obtained by means of electron microprobe analysis. In connection with data evaluation they present numerical calculations assessing the accuracy of the Matano analysis and the thin-film solution of Fick`s 2nd law as function of the thickness of the initial diffusant layer. The results are of general interest, particularly for the evaluation of diffusion measurements involving industrial specimens with given geometry.

  11. FeAl-TiC and FeAl-WC composites - melt infiltration processing, microstructure and mechanical properties

    SciTech Connect

    Subramanian, R.; Schneibel, J.H.

    1997-04-01

    TiC-based and WC-based cermets were processed with iron aluminide, an intermetallic, as a binder by pressureless melt infiltration to near full density (> 97 % theoretical density). Phase equilibria calculations in the quaternary Fe-Al-Ti-C and Fe-Al-W-C systems at 145{degrees}C were performed to determine the solubility of the carbide phases in liquid iron aluminide. This was done by using Thermocalc{trademark} and the results show that molten Fe-40 at.% Al in equilibrium with Ti{sub 0.512}C{sub 0.488} and graphite, dissolves 4.9 at% carbon and 64 atomic ppm titanium. In the Fe-Al-W-C system, liquid Fe-40 at.% Al in equilibrium with graphite dissolves about 5 at.% carbon and 1 at.% tungsten. Due to the low values for the solubility of the carbide phases in liquid iron aluminide, liquid phase sintering of mixed powders does not yield a dense, homogeneous microstructure for carbide volume fractions greater than 0.70. Melt infiltration of molten FeAl into TiC and WC preforms serves as a successful approach to process cermets with carbide contents ranging from 70 to 90 vol. %, to greater than 97% of theoretical density. Also, the microstructures of cermets prepared by melt infiltration were very homogeneous. Typical properties such as hardness, bend strength and fracture toughness are reported. SEM observations of fracture surfaces suggest the improved fracture toughness to result from the ductility of the intermetallic phase. Preliminary experiments for the evaluation of the oxidation resistance of iron aluminide bonded cermets indicate that they are more resistant than WC-Co cermets.

  12. Coverage effects on the magnetism of Fe/MgO(001) ultrathin films

    SciTech Connect

    Martinez Boubeta, C.; Clavero, C.; Garcia-Martin, J.M.; Armelles, G.; Cebollada, A.; Balcells, Ll.; Menendez, J.L.; Peiro, F.; Cornet, A.; Toney, Michael F.

    2005-01-01

    Different aspects of the structure-magnetism and morphology-magnetism correlation in the ultrathin limit are studied in epitaxial Fe films grown on MgO(001). In the initial stages of growth the presence of substrate steps, intrinsically higher than an Fe atomic layer, prevent the connection between Fe islands and hence the formation of large volume magnetic regions. This is proposed as an explanation to the superparamagnetic nature of ultrathin Fe films grown on MgO in addition to the usually considered islanded, or Vollmer-Weber, growth. Using this model, we explain the observed transition from superparamagnetism to ferromagnetism for Fe coverages above 3 monolayers (ML). However, even though ferromagnetism and magnetocrystalline anisotropy are observed for 4 ML, complete coverage of the MgO substrate by the Fe ultrathin films only occurs around 6 ML as determined by polar Kerr spectra and simulations that consider different coverage situations. In annealed 3.5 ML Fe films, shape or configurational anisotropy dominates the intrinsic magnetocrystalline anisotropy, due to an annealing induced continuous to islanded morphological transition. A small interface anisotropy in thicker films is observed, probably due to dislocations observed at the Fe/MgO(001) interface.

  13. Corrosion and protection of heterogeneous cast Al-Si (356) and Al-Si-Cu-Fe (380) alloys by chromate adn cerium inhibitors

    NASA Astrophysics Data System (ADS)

    Jain, Syadwad

    In this study, the localized corrosion and conversion coating on cast alloys 356 (Al-7.0Si-0.3Mg) and 380 (Al-8.5Si-3.5Cu-1.6Fe) were characterized. The intermetallic phases presence in the permanent mold cast alloy 356 are primary-Si, Al5FeSi, Al8Si6Mg3Fe and Mg2Si. The die cast alloy 380 is rich in Cu and Fe elements. These alloying elements result in formation of the intermetallic phases Al 5FeSi, Al2Cu and Al(FeCuCr) along with primary-Si. The Cu- and Fe-rich IMPS are cathodic with respect to the matrix phase and strongly govern the corrosion behavior of the two cast alloys in an aggressive environment due to formation of local electrochemical cell in their vicinity. Results have shown that corrosion behavior of permanent mould cast alloy 356 is significantly better than the die cast aluminum alloy 380, primarily due to high content of Cu- and Fe-rich phases such as Al2Cu and Al 5FeSi in the latter. The IMPS also alter the protection mechanism of the cast alloys in the presence of inhibitors in an environment. The presence of chromate in the solution results in reduced cathodic activity on all the phases. Chromate provides some anodic inhibition by increasing pitting potentials and altering corrosion potentials for the phases. Results have shown that performance of CCC was much better on 356 than on 380, primarily due to inhomogeneous and incomplete coating deposition on Cu- and Fe- phases present in alloy 380. XPS and Raman were used to characterize coating deposition on intermetallics. Results show evidence of cyanide complex formation on the intermetallic phases. The presence of this complex is speculated to locally suppress CCC formation. Formation and breakdown of cerium conversion coatings on 356 and 380 was also analyzed. Results showed that deposition of cerium hydroxide started with heavy precipitation on intermetallic particles with the coatings growing outwards onto the matrix. Electrochemical analysis of synthesized intermetallics compounds in the

  14. Spin crossover in liquid (Mg,Fe)O at extreme conditions

    NASA Astrophysics Data System (ADS)

    Holmström, E.; Stixrude, L.

    2016-05-01

    We use first-principles free-energy calculations to predict a pressure-induced spin crossover in the liquid planetary material (Mg,Fe)O, whereby the magnetic moments of Fe ions vanish gradually over a range of hundreds of GPa. Because electronic entropy strongly favors the nonmagnetic low-spin state of Fe, the crossover has a negative effective Clapeyron slope, in stark contrast to the crystalline counterpart of this transition-metal oxide. Diffusivity of liquid (Mg,Fe)O is similar to that of MgO, displaying a weak dependence on element and spin state. Fe-O and Mg-O coordination increases from approximately 4 to 7 as pressure goes from 0 to 200 GPa. We find partitioning of Fe to induce a density inversion between the crystal and melt, implying separation of a basal magma ocean from a surficial one in the early Earth. The spin crossover induces an anomaly into the density contrast, and the oppositely signed Clapeyron slopes for the crossover in the liquid and crystalline phases imply that the solid-liquid transition induces a spin transition in (Mg,Fe)O.

  15. Spectroscopic studies of synthetic and natural ringwoodite, γ-(Mg, Fe)2SiO4

    NASA Astrophysics Data System (ADS)

    Taran, Michail N.; Koch-Müller, Monika; Wirth, Richard; Abs-Wurmbach, Irmgard; Rhede, Dieter; Greshake, Ansgar

    2009-04-01

    Synthetic ringwoodite γ-(Mg1- x Fe x )2SiO4 of 0.4 ≤ x ≤ 1.0 compositions and variously colored micro-grains of natural ringwoodite in shock metamorphism veins of thin sections of two S6-type chondrites were studied by means of microprobe analysis, TEM and optical absorption spectroscopy. Three synthetic samples were studied in addition with Mössbauer spectroscopy. The Mössbauer spectra consist of two doublets caused by VIFe2+ and VIFe3+, with IS and QS parameters close to those established elsewhere (e.g., O’Neill et al. in Am Mineral 78:456-460, 1993). The Fe3+/Fetotal ratio evaluated by curve resolution of the spectra, ranges from 0.04 to 0.1. Optical absorption spectra of all synthetic samples studied are qualitatively very similar as they are directly related to the iron content. They differ mostly in the intensity of the observed absorption features. The spectra consist of a very strong high-energy absorption edge and a series of absorption bands of different width and intensity. The three strongest and broadest absorptions of them are attributed to splitting of electronic spin-allowed 5 T 2g → 5 E g transitions of VIFe2+ and intervalence charge-transfer (IVCT) transition between ferrous and ferric ions in adjacent octahedral sites of the ringwoodite structure. The spin-allowed bands at ca. 8,000 and 11,500 cm-1 weakly depend on temperature, whilst the Fe2+/Fe3+ IVCT band at ~16,400 cm-1 displays very strong temperature dependence: i.e., with increasing temperature it decreases and practically disappears at about 497 K, a behavior typical for bands of this type. With increasing pressure the absorption edge shifts to lower energies while the spin-allowed bands shift to higher energy and strongly decreases in intensity. The IVCT band also strongly weakens and vanishes at about 9 GPa. We assigned this effect to pressure-induced reduction of Fe3+ in ringwoodite. By analogy with synthetic samples three broad bands in spectra of natural (meteoritic) blue

  16. Superparamagnetic mesoporous Mg-Fe bi-metal oxides as efficient magnetic solid-base catalysts for Knoevenagel condensations.

    PubMed

    Gao, Zhe; Zhou, Jian; Cui, Fangming; Zhu, Yan; Hua, Zile; Shi, Jianlin

    2010-12-14

    Superparamagnetic mesoporous Mg-Fe bi-metal oxides with varied Mg-Fe atomic ratios have been successfully synthesized as solid base catalysts. The M2F-400 catalyst with Mg/Fe atomic ratio = 2 showed extraordinarily high activities for Knoevenagel reactions even at room temperature. It could be magnetically separated, recycled, and reused for at least five cycles.

  17. Spin-transfer switching in full-Heusler Co2FeAl-based magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Sukegawa, Hiroaki; Wen, Zhenchao; Kondou, Kouta; Kasai, Shinya; Mitani, Seiji; Inomata, Koichiro

    2012-04-01

    We demonstrated spin-transfer magnetization switching using magnetic tunnel junctions (MTJs) with a full-Heusler alloy Co2FeAl (CFA). We prepared CFA (1.5 nm)/MgO/CoFe (4 nm) ("CFA-free") and CFA (30 nm)/MgO/CoFeB (2 nm) ("CFA-reference") MTJs on a Cr(001) layer. The intrinsic critical current density (Jc0) of the CFA-free (CFA-reference) MTJ was 29 MA/cm2 (7.1 MA/cm2). The larger Jc0 of the CFA-free MTJ is attributed to the significant enhancement of the Gilbert damping factor (˜0.04) of the CFA due to the Cr layer. The Jc0 of the CFA-reference is as small as that reported for typical CoFeB/MgO/CoFeB MTJs.

  18. Magnetic Tunnel Junctions with Perpendicular Anisotropy Using a Co2FeAl Full-Heusler Alloy

    NASA Astrophysics Data System (ADS)

    Wen, Zhenchao; Sukegawa, Hiroaki; Kasai, Shinya; Hayashi, Masamitsu; Mitani, Seiji; Inomata, Koichiro

    2012-06-01

    We fabricated perpendicularly magnetized magnetic tunnel junctions (p-MTJs) with an ultrathin Co2FeAl (CFA) full-Heusler alloy electrode having large interface magnetic anisotropy of CFA/MgO. An out-of-plane tunnel magnetoresistance (TMR) ratio of 53% at room temperature was observed in CFA/MgO/Co20Fe60B20 p-MTJs. By inserting a 0.1-nm-thick Fe (Co50Fe50) layer between the MgO and Co20Fe60B20 layers, The TMR ratio was significantly enhanced to 91% (82%) due to the improved interface. The bias voltage dependence of differential conductance did not clearly show coherent tunneling characteristics for ultrathin CFA-MTJs, suggesting that a higher TMR ratio may be achieved by improving the B2 ordering of CFA and/or interface structure.

  19. First-principles study of Fe and FeAl defects in SiGe alloys

    SciTech Connect

    Carvalho, A.; Coutinho, J.; Barroso, M.; Jones, R.; Goss, J.; Briddon, P. R.

    2008-09-15

    First-principles, spin-polarized local-density-functional calculations are used to model interstitial iron (Fe{sub i}) and its complexes with substitutional aluminum in dilute Si{sub x}Ge{sub 1-x} alloys (x<8%). We considered both the effect of direct bonding between Fe{sub i} or Fe{sub i}Al with Ge atoms in the x{yields}0 limit and the evolution of the defect properties with the alloy composition. It is found that Fe{sub i} prefers Si-rich regions, but when placed near a Ge atom, its (0/+) level is shifted toward the conduction band. However, the ionization energy of Fe{sup (+/+2)}-Al{sup -} is only slightly changed by the presence of neighboring Ge atoms in the proximity. It is also found that indirect alloying effects shift the donor levels of Fe{sub i} and FeAl at a fast rate toward the valence band. The acceptor levels, however, remain approximately at the same distance from E{sub v}.

  20. Quantum-mechanical calculation of the solid-state equilibrium MgO+α-Al2O3⇄MgAl2O4 (spinel) versus pressure

    NASA Astrophysics Data System (ADS)

    Catti, M.; Valerio, G.; Dovesi, R.; Causà, M.

    1994-05-01

    The ground-state crystal energies of cubic MgAl2O4 (spinel) and MgO (periclase) and of rhombohedral α-Al2O3 (corundum) have been calculated at different volumes, relaxing the corresponding structures, by all-electron periodic Hartree-Fock methods (crystal program). Basis sets of contracted Gaussian-type functions are employed for the 18 atomic (including d) orbitals representing each of the Mg, Al, and O atoms. Mulliken net atomic charges zMg=1.86||e|| (MgO), zAl=2.30||e|| (α-Al2O3), zMg=1.74||e||, and zAl=2.24||e|| (spinel) are obtained. The elastic bulk modulus, the Murnaghan equation of state p(V) at the athermal limit, the Mg-O and Al-O bond compressibilities, and the binding energy have been derived for each phase (and the elastic constants C11 and C12 for spinel only). Comparison with existing experimental data is discussed. The enthalpy change for spinel decomposition into the simple oxides has been computed as a function of pressure, including a correction for the electron correlation energy based on local-density-functional theory. A decomposition pressure of 11 GPa at T=0 K is predicted, against values of 8 and 13 GPa derived from experimental thermodynamic data and from direct compression experiments, respectively.

  1. Thermodynamics of O, N, and S in liquid Fe equilibrated with CaO-AI2O3-MgO slags

    NASA Astrophysics Data System (ADS)

    Inoue, Ryo; Suito, Hideaki

    1994-04-01

    Nitrogen and S distribution ratios between CaO-Al2O3-MgO slags and liquid Fe were measured at 1873 K as a function of Al (or Mg, Ca) content in metal, using CaO, MgO, and A12O3 crucibles. Based on the results for the solubility product of MgO, the equilibrium constant, K Mg , for the reaction MgO = Mg + O and the first-order interaction parameter, e {O/Mg} ( e {Mg/O}), were estimated to be log K Mg = -7.8 ± 0.2 and e {O/Mg} = -190 ± 60 ( e {Mg/O} = -290 ± 90), respectively. The activities of A12O3 at the slag compositions double-saturated with CaO/MgO, MgO/ MgO A12O3, and MgO Al2O3/CaO 2A12O3 components were obtained from the S distribution ratios between slag and metal, coupled with the reported values of sulfide capacities. Nitride capacities were also estimated from the N distribution ratios and the activities of A12O3.

  2. Processing and properties of FeAl-bonded composites

    SciTech Connect

    Schneibel, J.H.; Subramanian, R.; Alexander, K.B.; Becher, P.F.

    1996-12-31

    Iron aluminides are thermodynamically compatible with a wide range of ceramics such as carbides, borides, oxides, and nitrides, which makes them suitable as the matrix in composites or cermets containing fine ceramic particulates. For ceramic contents varying from 30 to 60 vol.%, composites of Fe-40 at. % Al with WC, TiC, TiB{sub 2}, and ZrB{sub 2} were fabricated by conventional liquid phase sintering of powder mixtures. For ceramic contents from 70 to 85 vol.%, pressureless melt infiltration was found to be a more suitable processing technique. In FeAl-60 vol.% WC, flexure strengths of up to 1.8 GPa were obtained, even though processing defects consisting of small oxide clusters were present. Room temperature fracture toughnesses were determined by flexure testing of chevron-notched specimens. FeAl/WC and FeAl/TiC composites containing 60 vol.% carbide particles exhibited K{sub Q} values around 20 MPa m{sup 1/2}. Slow crack growth measurements carried out in water and in dry oxygen suggest a relatively small influence of water-vapor embrittlement. It appears therefore that the mechanical properties of iron aluminides in the form of fine ligaments are quite different from their bulk properties. Measurements of the oxidation resistance, dry wear resistance, and thermal expansion of iron aluminide composites suggest many potential applications for these new materials.

  3. Resolving the stellar sources of isotopically rare presolar silicate grains through Mg and Fe isotopic analyses

    SciTech Connect

    Nguyen, Ann N.; Messenger, Scott

    2014-04-01

    We conducted multi-element isotopic analyses of 11 presolar silicate grains from the Acfer 094 meteorite having unusual O isotopic compositions. Eight grains are {sup 18}O-rich, one is {sup 16}O-rich, and two are extremely {sup 17}O-rich. We constrained the grains' stellar sources by measuring their Si and Mg isotopic ratios, and also the {sup 54}Fe/{sup 56}Fe and {sup 57}Fe/{sup 56}Fe ratios for five grains. The Mg and Fe isotopic measurements were conducted after surrounding matrix grains were removed for more accurate ratios. Most of the {sup 18}O-rich silicates had anomalous Mg isotopic ratios, and their combined isotopic constraints are consistent with origins in low-mass Type II supernovae (SNe II) rather than high-metallicity stars. The isotopic ratios of the {sup 16}O-rich silicate are also consistent with an SN origin. Mixing small amounts of interior stellar material with the stellar envelope replicated all measured isotopic ratios except for {sup 29}Si/{sup 28}Si and {sup 54}Fe/{sup 56}Fe in some grains. The {sup 29}Si/{sup 28}Si ratios of all SN-derived grains are matched by doubling the {sup 29}Si yield in the Ne- and Si-burning zones. The {sup 54}Fe/{sup 56}Fe ratios of the grains imply elemental fractionation in the Si/S zone, or introduction of isotopically solar Fe by secondary processing. The two highly {sup 17}O-rich silicates exhibited significant {sup 25}Mg and/or {sup 26}Mg enrichments and their isotopic ratios are best explained by strong dilution of 1.15 M {sub ☉} CO nova matter. We estimate that ∼12% and 1% of presolar silicates have SN and nova origins, respectively, similar to presolar SiC and oxides. This implies that asymptotic giant branch stars are the dominant dust producers in the galaxy.

  4. Nucleosynthesis in AGB stars: Observation of Mg-25 and Mg-26 in IRC+10216 and possible detection of Al-26

    NASA Technical Reports Server (NTRS)

    Guelin, M.; Forestini, M.; Valiron, P.; Ziurys, L. M.; Anderson, M. A.; Cernicharo, J.; Kahane, C.

    1995-01-01

    We report the detection in the circumstellar envelope IRC+10216 of millimeter lines of the rare isotopomers (25)MgNC and (26)MgNC, as well as of a line at 234433 MHz, which could be the J= 7-6 transition of (26)AlF (an alternate, although less likely identified would be the J= 9-8 transition of NaF). The derived Mg-24:Mg-25:Mg-26 isotopic abundance ratios (78 : 11+/- 1 : 11 +/-1) are consistent with the solar system values (79.0:10.0:11.0), following Anders & Grevesse 1989). According to new calculations of evolutionary models of 3 solar mass and 5 solar mass asymptotic giant branch (AGB) stars, these ratios and the previously measured N, O and Si isotopic ratios imply that the central star had an initial mass 3 solar mass (less than or equal to M(sub *, ini) less than 5 solar mass and has already experienced many 3rd dredge-up events. From this, it can be predicted that the Al-26/Al-27 isotopics ratio lies between 0.01 and 0.08; in fact, the value derived in the case that U234433 arises from (26)AlF is Al-26/Al-27 = 0.04. The identification of the (25)MgNC and (26)MgNC lines was made possible by ab-initio quantum mechanical calculations of the molecule geometrical structure. It was confirmed through millimeter-wave laboratory measurements. The quantum mechanical calculations are briefly described and the laboratory results presented in some detail. The rotation constants B, D, H and the spin-rotation constant gamma of (25)MgNC and (26)MgNC are determined from a fit of laboratory and astronomical data.

  5. The Systematics of Activity-Composition Relations in Mg-Fe2+ Oxide and Silicate Solid Solutions

    NASA Astrophysics Data System (ADS)

    O'Neill, H. S.

    2006-12-01

    accuracy including possible systematic errors of 0.5 kJ/mol (1 st. dev.). Any asymmetry is unambiguously constrained to be very small. These results were combined with experimental data (all at or above 900ºC), for partitioning of Mg and Fe between olivine and one of ilmenite (Pownceby and O'Neill, in prep.), Ti-, Al- or Cr-spinel (O'Neill, unpublished) and pyroxenes, garnet, and various high-pressure phases (literature). Internal consistency can be checked using other available partitioning data between pairs of these phases (i.e., without olivine). Except for some of the high-pressure phases, the ferromagnesian solutions are symmetrical with W Mg-Fe decreasing with the difference in the volumes of the end-members, which in turn depends on the atomic (Mg+Fe)/O ratio. This suggests that mixing in binary amphiboles, micas and other complex ferromagnesian silicates should be nearly ideal. The discrepancies shown by the high-pressure phases may be due to Fe3+ substitutions. As a working hypothesis, it is proposed that solid solutions between cations of the same charge and roughly similar size have simple thermodynamic mixing properties, with little asymmetry, modest excess entropies and excess enthalpies proportional to the volume difference of the end-members. Order-disorder phenomena have surprisingly little effect in the high temperature regime for which experimental data are available. Refs: [1] Davies and Navrotsky, J Sol State Chem 46, 1-22, 1983. [2] O'Neill et al., CMP 146, 308-325, 2003.

  6. Carbon Nanostructures Grown on Fe-Cr-Al Alloy

    NASA Astrophysics Data System (ADS)

    Čaplovičová, Mária; Čaplovič, Ľubomír; Búc, Dalibor; Vinduška, Peter; Janík, Ján

    2010-11-01

    The morphology and nanostructure of carbon nanotubes (CNTs), synthesized directly on Fe-Cr-Al-based alloy substrate using an alcohol catalytic chemical vapour deposition method (ACCVD), were examined by transmission electron microscopy (TEM). The grown CNTs were entangled with chain-like, bamboo-like, and necklace-like morphologies. The CNT morphology was affected by the elemental composition of catalysts and local instability of deposition process. Straight and bended CNTs with bamboo-like nanostructure grew mainly on γ-Fe and Fe3C particles. The synthesis of necklace-like nanostructures was influenced by silicon oxide, and growth of chain-like nanostructures was supported by a catalysts consisting of Fe, Si, oxygen and trace of Cr. Most of nanotubes grew according to base growth mechanism.

  7. Development of ODS-Fe{sub 3}Al alloys

    SciTech Connect

    Wright, I.G.; Pint, B.A.; Tortorelli, P.F.; McKamey, C.G.

    1997-12-01

    The overall goal of this program is to develop an oxide dispersion-strengthened (ODS) version of Fe{sub 3}Al that has sufficient creep strength and resistance to oxidation at temperatures in the range 1000 to 1200 C to be suitable for application as heat exchanger tubing in advanced power generation cycles. The main areas being addressed are: (a) alloy processing to achieve the desired alloy grain size and shape, and (b) optimization of the oxidation behavior to provide increased service life compared to semi-commercial ODS-FeCrAl alloys intended for the same applications. The recent studies have focused on mechanically-alloyed powder from a commercial alloy vendor. These starting alloy powders were very clean in terms of oxygen content compared to ORNL-produced powders, but contained similar levels of carbon picked up during the milling process. The specific environment used in milling the powder appears to exert a considerable influence on the post-consolidation recrystallization behavior of the alloy. A milling environment which produced powder particles having a high surface carbon content resulted in a consolidated alloy which readily recrystallized, whereas powder with a low surface carbon level after milling resulted in no recrystallization even at 1380 C. A feature of these alloys was the appearance of voids or porosity after the recrystallization anneal, as had been found with ORNL-produced alloys. Adjustment of the recrystallization parameters did not reveal any range of conditions where recrystallization could be accomplished without the formation of voids. Initial creep tests of specimens of the recrystallized alloys indicated a significant increase in creep strength compared to cast or wrought Fe{sub 3}Al, but the specimens failed prematurely by a mechanism that involved brittle fracture of one of the two grains in the test cross section, followed by ductile fracture of the remaining grain. The reasons for this behavior are not yet understood. The

  8. Nanowires of Fe/multi-walled carbon nanotubes and nanometric thin films of Fe/MgO

    SciTech Connect

    Newman, Alexander; Khatiwada, Suman; Neupane, Suman; Seifu, Dereje

    2015-04-14

    We observed that nanowires of Fe grown in the lumens of multi-walled carbon nanotubes required four times higher magnetic field strength to reach saturation compared to planar nanometric thin films of Fe on MgO(100). Nanowires of Fe and nanometric thin films of Fe both exhibited two fold magnetic symmetries. Structural and magnetic properties of 1-dimensional nanowires and 2-dimensional nanometric films were studied by several magnetometery techniques. The θ-2θ x-ray diffraction measurements showed that a (200) peak of Fe appeared on thin film samples deposited at higher substrate temperatures. In these samples prepared at higher temperatures, lower coercive field and highly pronounced two-fold magnetic symmetry were observed. Our results show that maximum magnetocrystalline anisotropy occurred for sample deposited at 100 °C and it decreased at higher deposition temperatures.

  9. Nanowires of Fe/multi-walled carbon nanotubes and nanometric thin films of Fe/MgO

    NASA Astrophysics Data System (ADS)

    Newman, Alexander; Khatiwada, Suman; Neupane, Suman; Seifu, Dereje

    2015-04-01

    We observed that nanowires of Fe grown in the lumens of multi-walled carbon nanotubes required four times higher magnetic field strength to reach saturation compared to planar nanometric thin films of Fe on MgO(100). Nanowires of Fe and nanometric thin films of Fe both exhibited two fold magnetic symmetries. Structural and magnetic properties of 1-dimensional nanowires and 2-dimensional nanometric films were studied by several magnetometery techniques. The θ-2θ x-ray diffraction measurements showed that a (200) peak of Fe appeared on thin film samples deposited at higher substrate temperatures. In these samples prepared at higher temperatures, lower coercive field and highly pronounced two-fold magnetic symmetry were observed. Our results show that maximum magnetocrystalline anisotropy occurred for sample deposited at 100 °C and it decreased at higher deposition temperatures.

  10. Taming the resistive switching in Fe/MgO/V/Fe magnetic tunnel junctions: An ab initio study

    NASA Astrophysics Data System (ADS)

    Aguiar-Hualde, J. M.; Alouani, M.

    2014-12-01

    A possible mechanism for the resistive switching observed experimentally in Fe/MgO/V/Fe junctions is presented. Ab initio total energy calculations within the local density approximation and pseudopotential theory shows that by moving the oxygen ions across the MgO/V interface one obtains a metastable state. It is argued that this state can be reached by applying an electric field across the interface. In addition, the ground state and the metastable state show different electric conductances. The latter results are discussed in terms of the changes of the density of states at the Fermi level and the charge transfer at the interface due to the oxygen ion motion.

  11. Increase in spin injection efficiency of a CoFe/MgO(100) tunnel spin injector with thermal annealing

    SciTech Connect

    Wang, R.; Jiang, X.; Shelby, R.M.; Macfarlane, R.M.; Parkin, S.S.P.; Bank, S.R.; Harris, J.S.

    2005-01-31

    Postgrowth thermal annealing of a CoFe/MgO(100) tunnel spin injector grown on aGaAs/AlGaAs quantum well structure results in a significantly increased spin injection efficiency as inferred from the polarization of heavy-hole electroluminescence from a quantum well optical detector. The as-deposited sample displayed an initial polarization at 100 K of 43%, which was increased to 52% after a 1 h anneal at 300 deg. C, and finally to 55% after a second 1 h anneal at 340 deg. C. The polarization remained unchanged upon further annealing to temperatures as high as 400 deg. C. These results show that tunnel spin injectors based on CoFe/MgO are robust with high thermal stability, making them useful for device applications.

  12. Preparation Behavior of the Mg-Fe Hydrotalcite by Urea Method and Its Cr(VI) Sorption Property.

    PubMed

    Xu, Sheng; Liao, MengChen; Zeng, HongYan; Liu, XiaoJun; Zhu, PeiHan; Chen, ChaoRong; Duan, HengZhi

    2016-03-01

    The hydrotalcite of Mg6Fe2(OH)16CO3 x 4.5H2O were synthesized using urea method by adjusting the initial pH and urea amount in the reaction solution. The results showed that the co-precipitation of Mg2+ with Fe3+ cations formed Mg-Fe LDH occurring at pH 8.48-9.35. The pH played a crucial role in the Mg-Fe LDH precipitation by controlling urea/Fe3+ molar ratio in the reaction solution at 105 degrees C. The optimized urea/Fe3+ molar ratio was 12.0, where the relative yield of the Mg-Fe LDH was 80.0% and the Mg-Fe LDH was highly crystalline with small particle sizes (1-2 μm). The affinity of the Mg-Fe mixed oxide (Mg-Fe LDO) with Cr(VI) was studied as a function of contact time, initial pH, temperature of the solutions and calcined time of Mg-Fe LDH. The adsorption conditions were optimized using response surface methodology. The maximum adsorption capacity of 38.86 mg/g was achieved at 85 min with the conditions of initial pH 5.5, temperature 55 degrees C and calcined time 4 h. It was concluded that the Mg-Fe LDO can be used as an adsorbent to removal Cr(VI) in aqueous solutions.

  13. Magnesium doping on brownmillerite Ca{sub 2}FeAlO{sub 5}

    SciTech Connect

    Malveiro, J.; Ramos, T.; Ferreira, L.P.; Waerenborgh, J.C.

    2007-06-15

    Ca{sub 2}FeAl{sub 1-} {sub x} Mg {sub x} O{sub 5} (x=0, 0.05 and 0.1) compounds adopting the brownmillerite-type structure were prepared by a self-combustion route using two different fuels. Characterisation was performed using X-ray powder diffraction, Moessbauer spectroscopy, magnetisation measurements, chemical analysis, scanning electron microscopy and 4-point dc conductivity measurements. Global results indicate that the solubility limit was reached for x=0.1. An antiferromagnetic behaviour was detected for all studied compositions, with magnetic ordering temperatures of 340 and 290 K for x=0 and 0.05, respectively. Mg doping increases the number of iron cations in tetrahedral sites, which induces magnetisation enhancement at low temperatures through the coupling between octahedral iron cations in different octahedral planes. The compounds exhibit semiconductor behaviour and Mg{sup 2+} doping yields a significant enhancement of the total conductivity, which can be essentially attributed to the presence of Fe{sup 4+} ions. - Graphical abstract: Ca{sub 2}FeAl{sub 1-} {sub x} Mg {sub x} O{sub 5} (x=0, 0.05, 0.1) compounds with the brownmillerite structure were prepared and characterised. The paramagnetic Moessbauer spectra presented were obtained at T=363 K (x=0); T=297 K (x=0.05) and T=353 K (x=0.1)

  14. Equation of State of Amorphous MgSiO3 and (MgFe)SiO3 to Lowermost Mantle Pressures

    NASA Astrophysics Data System (ADS)

    Sinmyo, R.; Petitgirard, S.; Malfait, W.; Kupenko, I.; Rubie, D. C.

    2014-12-01

    Melting phenomena have a crucial importance during the Earth's formation and evolution. For example, a deep magma ocean of 1000 km or more has lead to the segregation of the core. Tomographic images of the Earth reveal ultra-low velocity zones at the core-mantle boundary that may be due to the presence of dense magmas or remnant zones of a deep basal magma ocean [1]. Unfortunately, measurements of amorphous silicate density over the entire pressure regime of the mantle are scarce and the density contrast between solid and liquid are difficult to assess due to the lack of such data. Only few studies have reported density measurements of amorphous silicates at high-pressure, with limitation up to 60 GPa. High-pressure acoustic velocity measurements have been used to calculate the density of MgSiO3 glass up to 30 GPa [2] but exhibit a large discrepancy compared to recent calculations [3]. SiO2 glass was measured up to 55 GPa using the X-ray absorption method through the diamond anvils [4] and very recently, X-ray diffraction has been used to infer the density of basaltic melt up to 60 GPa [5]. Here we report density measurement of MgSiO3 glass up to 130 GPa and (MgFe)SiO3 glass up to 55 GPa using a novel variation of the X-ray absorption method. The sample contained in a beryllium gasket was irradiated with a micro-focus X-ray beam in two directions: perpendicular and parallel to the compression axis to obtain the absorption coefficient and density under pressure. Our data constrain the first experimental EoS for (Mg,Fe)SiO3 and the first EoS for MgSiO3 up to lowermost mantle pressures. Technical details and EoS parameters will be shown in the presentation. We will address the implications for melts in the deep Earth based on compressibility, bulk modulus and density contrasts between iron-free and iron-bearing glasses. [1] Labrosse S. et al. Nature 2007 [2] Sanchez-Valle C. et al. Earth Planet. Sc. Lett. 2010 [3] Ghosh D. et al Am. Mineral. 2014 [4] Sato T. et al

  15. Pseudosinhalite: discovery of the hydrous MgAl-borate as a new mineral in the Tayozhnoye, Siberia, skarn deposit

    NASA Astrophysics Data System (ADS)

    Schreyer, W.; Pertsev, N. N.; Medenbach, O.; Burchard, M.; Dettmar, D.

    After its initial synthesis as the new compound Mg2Al3B2O9(OH) (Daniels et al. 1997) pseudosinhalite has now been discovered as a new mineral. It occurs, together with hydrotalcite, as a replacement product of sinhalite, MgAlBO4, in an impure marble of the contact metasomatic iron boron deposit of Tayozhnoye in the Aldan Shield of Siberia. Its chemical composition determined by electron microprobe is (wt%): Al2O3 46.88; MgO 25.12; FeO 1.99; B2O3 (calculated) 21.75; H2O (calculated) 2.81 giving a total of 98.55 and leading to the empirical formula (Mg2.00 Fe2+0.09)Σ=2.09 Al2.94 B2O9(OH). The small deviation from the ideal stoichiometry with (Mg+Fe2+):Al≠2:3 may be caused by either solid solution towards, or submicroscopic interlayering with lamellae of, the structurally similar mineral sinhalite. The underlying substitution involving also B and H would be (Mg+Fe)+B=Al+2H. Pseudosinhalite is monoclinic, space group P21/c, with a=7.49(1), b=4.33(1), c=9.85(2) Å β=110.7(1)° V=299(1) Å3 Z=2. Calculated density is 3.508g/cm3. Pseudosinhalite is colourless with white streak and has a vitreous lustre. It is transparent; no fluorescence was detected. There is no cleavage and parting; fractures are concoidal. Optical constants could not be measured properly due to polysynthetic microtwinning, but α<1.72<γ. For synthetic pseudosinhalite α=1.691(1) β=1.713(1) γ=1.730(1) Δ=0.039 2V=80°. The temperature of pseudosinhalite formation was below about 400°C at low pressures and with a hydrous, CO2-bearing fluid participating in the reaction.

  16. Temperature, composition, and f O2 effects on intersite distribution of Mg and Fe2+ in olivines

    NASA Astrophysics Data System (ADS)

    Ottonello, G.; Princivalle, F.; Della Giusta, A.

    1990-09-01

    Single-crystal X-ray structure refinement of natural olivines equilibrated at high temperature under controlled oxygen fugacity ( f O2) conditions, coupled with a structure-energy model were used to establish the influence of T, f O2 and bulk chemistry on intracrystalline disorder. The results are: 1) The k D ( k D = [(Fe M1·Mg M2)/(Fe M2·Mg M1)]) factor describing site population on M1, M2 polyhedra increases from values lower than 1 at T below 400 600° C (depending on composition) to values higher than 1 at higher temperature. 2) The increase of k D with T is quite regular. 3) At constant temperature and pressure, k D increases with increasing fayalite content in the mixture; 4) Contrary to previous observations (Will and Nover 1979; Nover and Will 1981) varying f O2, within the stability range of the substance, has a negligible influence on intracrystalline disorder. 5) As ancillary results, the model confirms the defect scheme of Nakamura and Schmalzried (1983) for the investigated solids. Moreover, it shows that cationic vacancies are always created on M 1 site at the expense of Mg ions, while trivalent iron is always stabilized on M2 site. This explains the marked anisotropies observed in Fe-Mg interdiffusion (Buening and Busek 1973; Misener 1974; Schock et al. 1989).

  17. Synthesis and crystal structure of NaMgFe(MoO4)3

    PubMed Central

    Mhiri, Manel; Badri, Abdessalem; Ben Amara, Mongi

    2016-01-01

    The iron molybdate NaMgFe(MoO4)3 {sodium magnesium iron(III) tris­[molybdate(VI)]} has been synthesized by the flux method. This compound is isostructural with α-NaFe2(MoO4)3 and crystallizes in the triclinic space group P-1. Its structure is built up from [Mg,Fe]2O10 units of edge-sharing [Mg,Fe]O6 octa­hedra which are linked to each other through the common corners of [MoO4] tetra­hedra. The resulting anionic three-dimensional framework leads to the formation of channels along the [101] direction in which the Na+ cations are located. PMID:27308061

  18. Disproportionation of (Mg,Fe)SiO₃ perovskite in Earth's deep lower mantle.

    PubMed

    Zhang, Li; Meng, Yue; Yang, Wenge; Wang, Lin; Mao, Wendy L; Zeng, Qiao-Shi; Jeong, Jong Seok; Wagner, Andrew J; Mkhoyan, K Andre; Liu, Wenjun; Xu, Ruqing; Mao, Ho-kwang

    2014-05-23

    The mineralogical constitution of the Earth's mantle dictates the geophysical and geochemical properties of this region. Previous models of a perovskite-dominant lower mantle have been built on the assumption that the entire lower mantle down to the top of the D″ layer contains ferromagnesian silicate [(Mg,Fe)SiO3] with nominally 10 mole percent Fe. On the basis of experiments in laser-heated diamond anvil cells, at pressures of 95 to 101 gigapascals and temperatures of 2200 to 2400 kelvin, we found that such perovskite is unstable; it loses its Fe and disproportionates to a nearly Fe-free MgSiO3 perovskite phase and an Fe-rich phase with a hexagonal structure. This observation has implications for enigmatic seismic features beyond ~2000 kilometers depth and suggests that the lower mantle may contain previously unidentified major phases. PMID:24855264

  19. Origin of Perpendicular Magnetic Anisotropy and Large Orbital Moment in Fe Atoms on MgO.

    PubMed

    Baumann, S; Donati, F; Stepanow, S; Rusponi, S; Paul, W; Gangopadhyay, S; Rau, I G; Pacchioni, G E; Gragnaniello, L; Pivetta, M; Dreiser, J; Piamonteze, C; Lutz, C P; Macfarlane, R M; Jones, B A; Gambardella, P; Heinrich, A J; Brune, H

    2015-12-01

    We report on the magnetic properties of individual Fe atoms deposited on MgO(100) thin films probed by x-ray magnetic circular dichroism and scanning tunneling spectroscopy. We show that the Fe atoms have strong perpendicular magnetic anisotropy with a zero-field splitting of 14.0±0.3  meV/atom. This is a factor of 10 larger than the interface anisotropy of epitaxial Fe layers on MgO and the largest value reported for Fe atoms adsorbed on surfaces. The interplay between the ligand field at the O adsorption sites and spin-orbit coupling is analyzed by density functional theory and multiplet calculations, providing a comprehensive model of the magnetic properties of Fe atoms in a low-symmetry bonding environment.

  20. Temperature dependence of the magnetoresistance in Fe/MgO core/shell nanoparticles

    NASA Astrophysics Data System (ADS)

    Martinez-Boubeta, C.; Balcells, Ll.; Valencia, S.; Schmitz, D.; Monty, C.; Martínez, B.

    2009-06-01

    The temperature dependence of magnetoresistance (MR) of powdered samples consisting of spherical Fe/MgO core/shell nanoparticles was analyzed. A change of the MR from normal at room temperature to inverse at low temperatures was observed. Concomitant with this, samples showed a sudden increase in the electrical resistance when approaching TV≈120 K, i.e., indicative of the Verwey transition temperature of Fe3O4. Thus, signaling the existence of magnetite at the Fe/MgO interface, further confirmed by means of x-ray magnetic circular dichroism. The change from normal to inverse MR is related to the increase in resistance of Fe3O4 on crossing the Verwey transition and reflects the negative spin polarization of Fe3O4.

  1. IMPACT OF A REVISED {sup 25}Mg(p, {gamma}){sup 26}Al REACTION RATE ON THE OPERATION OF THE Mg-Al CYCLE

    SciTech Connect

    Straniero, O.; Cristallo, S.; Imbriani, G.; DiLeva, A.; Limata, B.; Strieder, F.; Bemmerer, D.; Broggini, C.; Caciolli, A.; Corvisiero, P.; Costantini, H.; Lemut, A.; Formicola, A.; Gustavino, C.; Junker, M.; Elekes, Z.; Fueloep, Zs.; Gyuerky, Gy.; Gervino, G.; Guglielmetti, A.; and others

    2013-02-15

    Proton captures on Mg isotopes play an important role in the Mg-Al cycle active in stellar H-burning regions. In particular, low-energy nuclear resonances in the {sup 25}Mg(p, {gamma}){sup 26}Al reaction affect the production of radioactive {sup 26}Al{sup gs} as well as the resulting Mg/Al abundance ratio. Reliable estimations of these quantities require precise measurements of the strengths of low-energy resonances. Based on a new experimental study performed at the Laboratory for Underground Nuclear Astrophysics, we provide revised rates of the {sup 25}Mg(p, {gamma}){sup 26}Al{sup gs} and the {sup 25}Mg(p, {gamma}){sup 26}Al {sup m} reactions with corresponding uncertainties. In the temperature range 50-150 MK, the new recommended rate of {sup 26}Al {sup m} production is up to five times higher than previously assumed. In addition, at T = 100 MK, the revised total reaction rate is a factor of two higher. Note that this is the range of temperature at which the Mg-Al cycle operates in a H-burning zone. The effects of this revision are discussed. Due to the significantly larger {sup 25}Mg(p, {gamma}){sup 26}Al {sup m} rate, the estimated production of {sup 26}Al{sup gs} in H-burning regions is less efficient than previously obtained. As a result, the new rates should imply a smaller contribution from Wolf-Rayet stars to the galactic {sup 26}Al budget. Similarly, we show that the asymptotic giant branch (AGB) extra-mixing scenario does not appear able to explain the most extreme values of {sup 26}Al/{sup 27}Al, i.e., >10{sup -2}, found in some O-rich presolar grains. Finally, the substantial increase of the total reaction rate makes the hypothesis of self-pollution by massive AGBs a more robust explanation for the Mg-Al anticorrelation observed in globular-cluster stars.

  2. Study on photorefractive property of Mg:Fe:LiNbO3 crystal

    NASA Astrophysics Data System (ADS)

    Xu, Zhaopeng; Xu, Shiwen; Xu, Yuheng; Wang, Rui

    2005-02-01

    The congruent Fe (0.03%wt):LiNbO3 crystals doped with different concentration of MgO (0, 2, 4, 6 mol%) were grown by Czochralski method in air atmosphere. The ultraviolet-visible absorption spectra, infrared absorption spectra of the crystals were measured in order to analyze their structure. The absorption edge of the Mg: Fe: LiNbO3 crystals shifted to the ultraviolet band compared with that of Fe: LiNbO3. The OH- absorption peaks of I and II crystals located at about 3483cm-1, while those of III and IV crystals shifted to 3536cm-1. The mechanism of OH- absorption peak shifting was studied. The light scattering ability resistance of Mg: Fe: LiNbO3 crystal was observed by straightly observing transmission facula distortion method. It indicated that light scattering ability resistance of III crystals was three orders of magnitude higher than that of Fe: LiNbO3 crystals. The exponential gain coefficient, diffraction efficiency and respond time of Mg: Fe: LiNbO3 crystals were measured by two-wave-coupling technology. The results indicate that exponential gain coefficient of Mg: Fe: LiNbO3 crystal was almost four times as that of iron-doped LiNbO3 and the response time exhibited four times shorter than that of iron-doped LiNbO3. Furthermore, the dynamic range was also calculated by the expression: M # = (τe ∠√η)/τω. The results indicated that Mg (4 mol%): Fe:LiNbO3 was the most proper holographic recording media material among four crystals in the paper.

  3. Isothermal compression behavior of (Mg,Fe)O using neon as a pressure medium

    SciTech Connect

    Zhuravlev, Kirill K.; Jackson, J.M.; Wolf, A.S.; Wicks, J.K.; Yan, J.; Clark, S.M.

    2012-04-30

    We present isothermal volume compression behavior of two polycrystalline (Mg,Fe)O samples with FeO = 39 and 78 mol% up to {approx}90 GPa at 300 K using synchrotron X-ray diffraction and neon as a pressure-transmitting medium. For the iron-rich (Mg{sub 0.22}Fe{sub 0.78})O sample, a structural transition from the B1 structure to a rhombohedral structure was observed at 41.6 GPa, with no further indication of changes in structural or compression behavior changes up to 93 GPa. In contrast, a change in the compression behavior of (Mg{sub 0.61}Fe{sub 0.39})O was observed during compression at P {ge} 71 GPa and is indicative of a spin crossover occurring in the Fe{sup 2+} component of (Mg{sub 0.61}Fe{sub 0.39})O. The low-spin state exhibited a volume collapse of {approx}3.5%, which is a larger value than what was observed for a similar composition in a laser-heated NaCl medium. Upon decompression, the volume of the high-spin state was recovered at approximately 65 GPa. We therefore bracket the spin crossover at 65 {le} P (GPa) {le} 77 at 300 K (Mg{sub 0.61}Fe{sub 0.39})O. We observed no deviation from the B1 structure in (Mg{sub 0.61}Fe{sub 0.39})O throughout the pressure range investigated.

  4. Corrosion and Discharge Behaviors of Al-Mg-Sn-Ga-In in Different Solutions

    NASA Astrophysics Data System (ADS)

    Xiong, Hanqing; Yin, Xiang; Yan, Yang; Dai, Yilong; Fan, Sufeng; Qiao, Xueyan; Yu, Kun

    2016-08-01

    Al-0.5 wt.%Mg-0.08 wt.%Sn-0.05 wt.%Ga-0.05 wt.%In and Al-0.5 wt.%Mg-0.08 wt.%Sn-0.05 wt.%Ga alloys were prepared by melting, casting and cold rolling. Corrosion and discharge behaviors of the two experimental alloys were investigated by electrochemical measurement, self-corrosion rate measurement, air battery testing, and scanning electron microscopy. The results showed that Al-Mg-Sn-Ga-In alloy exhibited higher electrochemical activity than Al-Mg-Sn-Ga alloy in 2 M NaCl solution, while it showed lower electrochemical activity than Al-Mg-Sn-Ga alloy in 4 M NaOH solution. By comparison with the air battery based on Al-Mg-Sn-Ga alloy, the battery with Al-Mg-Sn-Ga-In alloy cannot exhibit better discharge performance in 4 M NaOH electrolyte. However, the performance of the air battery based on Al-Mg-Sn-Ga-In alloy was greatly improved due to the In-rich inclusions and the uniform corroded morphology in 2 M NaCl electrolyte. Thus, Al-Mg-Sn-Ga-In alloy was a good anode material for Al-air battery in 2 M NaCl electrolyte.

  5. Tribological Characteristics of Single-phase AlMgB14 and Nanocomposite AlMgB14-TiB2 Superhard Coatings

    SciTech Connect

    Qu, Jun; Blau, Peter Julian; Zhu, Dong; Cook, Bruce A; Elmoursi, Alaa A

    2008-01-01

    This study investigated the friction and wear characteristics of AlMgB14 and AlMgB14-TiB2 superhard coatings, produced by pulse laser deposition (PLD) and physical vapor deposition (PVD), respectively. Tests were conducted under unidirectional and reciprocating sliding against AISI 52100 bearing steel in both dry and oil-lubricated conditions. The AlMgB14 coating exhibited an encouraging but short-lived low friction stage (u = 0.2) in dry sliding. The AlMgB14-TiB2 coating reduced the wear rates by one order of magnitude for itself and three orders of magnitude for the counterface compared with the uncoated M2 tool steel in dry sliding. This nanocomposite coating also demonstrated significant extension (>2.5X) of the low friction (non-scuffing) stage in a lubricant starvation sliding.

  6. Fe/Mg smectite formation under acidic conditions on early Mars

    NASA Astrophysics Data System (ADS)

    Peretyazhko, T. S.; Sutter, B.; Morris, R. V.; Agresti, D. G.; Le, L.; Ming, D. W.

    2016-01-01

    Phyllosilicates of the smectite group detected in Noachian and early Hesperian terrains on Mars have been hypothesized to form under neutral to alkaline conditions. These pH conditions would also be favorable for formation of widespread carbonate deposits which have not been detected on Mars. We propose that smectite deposits on Mars formed under moderately acidic conditions inhibiting carbonate formation. We report here the first synthesis of Fe/Mg smectite in an acidic hydrothermal system [200 °C, pHRT ∼ 4 (pH measured at room temperature) buffered with acetic acid] from Mars-analogue, glass-rich, basalt simulant with and without aqueous Mg or Fe(II) addition under N2-purged anoxic and ambient oxic redox conditions. Synthesized Fe/Mg smectite was examined by X-ray-diffraction, Mössbauer spectroscopy, visible and near-infrared reflectance spectroscopy, scanning electron microscopy and electron microprobe to characterize mineralogy, morphology and chemical composition. Alteration of the glass phase of basalt simulant resulted in formation of the Fe/Mg smectite mineral saponite with some mineralogical and chemical properties similar to the properties reported for Fe/Mg smectite on Mars. Our experiments are evidence that neutral to alkaline conditions on early Mars are not necessary for Fe/Mg smectite formation as previously inferred. Phyllosilicate minerals could instead have formed under mildly acidic pH conditions. Volcanic SO2 emanation and sulfuric acid formation is proposed as the major source of acidity for the alteration of basaltic materials and subsequent formation of Fe/Mg smectite.

  7. Discrete Layer-by-Layer Magnetic Switching in Fe /MgO (001 ) Superlattices

    NASA Astrophysics Data System (ADS)

    Moubah, R.; Magnus, F.; Warnatz, T.; Palsson, G. K.; Kapaklis, V.; Ukleev, V.; Devishvili, A.; Palisaitis, J.; Persson, P. O. Å.; Hjörvarsson, B.

    2016-04-01

    We report on a discrete layer-by-layer magnetic switching in Fe /MgO superlattices driven by an antiferromagnetic interlayer exchange coupling. The strong interlayer coupling is mediated by tunneling through MgO layers with thicknesses up to at least 1.8 nm, and the coupling strength varies with MgO thickness. Furthermore, the competition between the interlayer coupling and magnetocrystalline anisotropy stabilizes both 90° and 180° periodic alignment of adjacent layers throughout the entire superlattice. The tunable layer-by-layer switching, coupled with the giant tunneling magnetoresistance of Fe /MgO /Fe junctions, is an appealing combination for three-dimensional spintronic memories and logic devices.

  8. Phase relations in the greenschist-blueschist-amphibolite-eclogite facies in the system Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O (NCFMASH), with application to metamorphic rocks from Samos, Greece

    NASA Astrophysics Data System (ADS)

    Will, Thomas; Okrusch, Martin; Schmädicke, Esther; Chen, Guoli

    Calculated phase equilibria among the minerals sodic amphibole, calcic amphibole, garnet, chloritoid, talc, chlorite, paragonite, margarite, omphacite, plagioclase, carpholite, zoisite/clinozoisite, lawsonite, pyrophyllite, kyanite, sillimanite, quartz and H2O are presented for the model system Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O (NCFMASH), which is relevant for many greenschist, blueschist, amphibolite and eclogite facies rocks. Using the activity-composition relationships for multicomponent amphiboles constrained by Will and Powell (1992), equilibria containing coexisting calcic and sodic amphiboles could be determined. The blueschist-greenschist transition reaction in the NCFMASH system, for example, is defined by the univariant reaction sodic amphibole + zoisite=calcic amphibole + chlorite + paragonite + plagioclase (+ quartz + H2O) occurring between approximately 420 and 450°C at 9.5 to 10kbar. The calculated petrogenetic grid is a valuable tool for reconstructing the PT-evolution of metabasic rocks. This is shown for rocks from the island of Samos, Greece. On the basis of mineral and whole rock analyses, PT-pseudosections were calculated and, together with the observed mineral assemblages and reaction textures, are used to reconstruct PT-paths. For rocks from northern Samos, pseudomorphs after lawsonite preserved in garnet, the assemblage sodic amphibole-garnet-paragonite-chlorite-zoisite-quartz and the retrograde appearance of albitic plagioclase and the formation of calcic amphibole around sodic amphibole constrain a clockwise PT-path that reaches its thermal maximum at some 520°C and 19kbar. The derived PT-trajectory indicates cooling during exhumation of the rocks and is similar to paths for rocks from the western part of the Attic-Cycladic crystalline complex. Rocks from eastern Samos indicate lower pressures and are probably related to high-pressure rocks from the Menderes Massif in western Turkey.

  9. Giant strain control of magnetoelectric effect in Ta|Fe|MgO.

    PubMed

    Odkhuu, Dorj

    2016-01-01

    The exploration of electric field controlled magnetism has come under scrutiny for its intriguing magnetoelectric phenomenon as well as technological advances in spintronics. Herein, the tremendous effect of an epitaxial strain on voltage-controlled perpendicular magnetic anisotropy (VPMA) is demonstrated in a transition-metal|ferromagnet|MgO (TM|FM|MgO) heterostructure from first-principles electronic structure computation. By tuning the epitaxial strain in Ta|Fe|MgO as a model system of TM|FM|MgO, we find distinctly different behaviours of VPMA from V- to Λ-shape trends with a substantially large magnetoelectric coefficient, up to an order of 10(3) fJV(-1)m(-1). We further reveal that the VPMA modulation under strain is mainly governed by the inherently large spin-orbit coupling of Ta 5d-Fe 3d hybridized orbitals at the TM|FM interface, although the Fe 3d-O 2p hybridization at the FM|MgO interface is partly responsible in determining the PMA of Ta|Fe|MgO. These results suggest that the control of epitaxial strain enables the engineering of VPMA, and provides physical insights for the divergent behaviors of VPMA and magnetoelectric coefficients found in TM|FM|MgO experiments. PMID:27597448

  10. Giant strain control of magnetoelectric effect in Ta|Fe|MgO

    NASA Astrophysics Data System (ADS)

    Odkhuu, Dorj

    2016-09-01

    The exploration of electric field controlled magnetism has come under scrutiny for its intriguing magnetoelectric phenomenon as well as technological advances in spintronics. Herein, the tremendous effect of an epitaxial strain on voltage-controlled perpendicular magnetic anisotropy (VPMA) is demonstrated in a transition-metal|ferromagnet|MgO (TM|FM|MgO) heterostructure from first-principles electronic structure computation. By tuning the epitaxial strain in Ta|Fe|MgO as a model system of TM|FM|MgO, we find distinctly different behaviours of VPMA from V- to Λ-shape trends with a substantially large magnetoelectric coefficient, up to an order of 103 fJV‑1m‑1. We further reveal that the VPMA modulation under strain is mainly governed by the inherently large spin-orbit coupling of Ta 5d–Fe 3d hybridized orbitals at the TM|FM interface, although the Fe 3d–O 2p hybridization at the FM|MgO interface is partly responsible in determining the PMA of Ta|Fe|MgO. These results suggest that the control of epitaxial strain enables the engineering of VPMA, and provides physical insights for the divergent behaviors of VPMA and magnetoelectric coefficients found in TM|FM|MgO experiments.

  11. Giant strain control of magnetoelectric effect in Ta|Fe|MgO

    PubMed Central

    Odkhuu, Dorj

    2016-01-01

    The exploration of electric field controlled magnetism has come under scrutiny for its intriguing magnetoelectric phenomenon as well as technological advances in spintronics. Herein, the tremendous effect of an epitaxial strain on voltage-controlled perpendicular magnetic anisotropy (VPMA) is demonstrated in a transition-metal|ferromagnet|MgO (TM|FM|MgO) heterostructure from first-principles electronic structure computation. By tuning the epitaxial strain in Ta|Fe|MgO as a model system of TM|FM|MgO, we find distinctly different behaviours of VPMA from V- to Λ-shape trends with a substantially large magnetoelectric coefficient, up to an order of 103 fJV−1m−1. We further reveal that the VPMA modulation under strain is mainly governed by the inherently large spin-orbit coupling of Ta 5d–Fe 3d hybridized orbitals at the TM|FM interface, although the Fe 3d–O 2p hybridization at the FM|MgO interface is partly responsible in determining the PMA of Ta|Fe|MgO. These results suggest that the control of epitaxial strain enables the engineering of VPMA, and provides physical insights for the divergent behaviors of VPMA and magnetoelectric coefficients found in TM|FM|MgO experiments. PMID:27597448

  12. Development of Fe-Mn-Al-X-C alloys

    NASA Technical Reports Server (NTRS)

    Schuon, S. R.

    1982-01-01

    Development of a low cost Cr-free, iron-base alloy for aerospace applications involves both element substitution and enhancement of microstructural strengthening. When Mn is substituted for Ni and Al or Si is substituted for Cr, large changes occur in the mechanical and thermal stability of austenite in FeMnAlC alloys. The in situ strength of MC or M2C (M = Ti, V, Hf, Ta, or Mo) in FeMnAlC alloys was determined. The high temperature tensile strength depends more on the distribution of carbides than the carbide composition. Precipitation of a high volume percent-ordered phase was achieved in Fe2OMnlONi6Al6Ti (lC) alloys. As case, these alloys have a homogeneous austenitic structure. After solutioning at 1100 C for 5 hr followed by aging at 600 C for 16 hr, gamma prime or a perovskite carbide is precipitated. Overaging occurs at 900 C where eta is precipitated.

  13. Investigation on the Interface Characteristics of Al/Mg Bimetallic Castings Processed by Lost Foam Casting

    NASA Astrophysics Data System (ADS)

    Jiang, Wenming; Li, Guangyu; Fan, Zitian; Wang, Long; Liu, Fuchu

    2016-05-01

    The lost foam casting (LFC) process was used to prepare the A356 aluminum and AZ91D magnesium bimetallic castings, and the interface characteristics of the reaction layer between aluminum and magnesium obtained by the LFC process were investigated in the present work. The results indicate that a uniform and compact interface between the aluminum and magnesium was formed. The reaction layer of the interface with an average thickness of approximately 1000 μm was mainly composed of Al3Mg2 and Al12Mg17 intermetallic compounds, including the Al3Mg2 layer adjacent to the aluminum insert, the Al12Mg17 middle layer, and the Al12Mg17 + δ eutectic layer adjacent to the magnesium base. Meanwhile, the Mg2Si intermetallic compound was also detected in the reaction layer. An oxide film mainly containing C, O, and Mg elements generated at the interface between the aluminum and magnesium, due to the decomposed residue of the foam pattern, the oxidations of magnesium and aluminum alloys as well as the reaction between the magnesium melt and the aluminum insert. The microhardness tests show that the microhardnesses at the interface were obviously higher than those of the magnesium and aluminum base metals, and the Al3Mg2 layer at the interface had a high microhardness compared with the Al12Mg17 and Al12Mg17 + δ eutectic layers, especially the eutectic layer.

  14. A study on atomic diffusion behaviours in an Al-Mg compound casting process

    SciTech Connect

    Liu, Yongning; Chen, Yiqing; Yang, Chunhui

    2015-08-15

    Al and Mg alloys are main lightweight alloys of research interest and they both have superb material properties, i.e., low density and high specific strength, etc. Being different from Al alloys, the corrosion of Mg alloys is much more difficult to control. Therefore to combine merits of these two lightweight alloys as a composite-like structure is an ideal solution through using Al alloys as a protective layer for Mg alloys. Compound casting is a realistic technique to manufacture such a bi-metal structure. In this study, a compound casting technique is employed to fabricate bi-layered samples using Al and Mg and then the samples are analysed using electron probe micro-analyzer (EPMA) to determine diffusion behaviours between Al and Mg. The diffusion mechanism and behaviours between Al and Mg are studied numerically at atomic scale using molecular dynamics (MD) and parametric studies are conducted to find out influences of ambient temperature and pressure on the diffusion behaviours between Al and Mg. The results obtained clearly show the effectiveness of the compound casting process to increase the diffusion between Al and Mg and thus create the Al-base protection layer for Mg.

  15. Natural dissociation of olivine to (Mg,Fe)SiO3 perovskite and magnesiowüstite in a shocked Martian meteorite

    PubMed Central

    Miyahara, Masaaki; Ohtani, Eiji; Ozawa, Shin; Kimura, Makoto; El Goresy, Ahmed; Sakai, Takeshi; Nagase, Toshiro; Hiraga, Kenji; Hirao, Naohisa; Ohishi, Yasuo

    2011-01-01

    We report evidence for the natural dissociation of olivine in a shergottite at high-pressure and high-temperature conditions induced by a dynamic event on Mars. Olivine (Fa34-41) adjacent to or entrained in the shock melt vein and melt pockets of Martian meteorite olivine-phyric shergottite Dar al Gani 735 dissociated into (Mg,Fe)SiO3 perovskite (Pv)+magnesiowüstite (Mw), whereby perovskite partially vitrified during decompression. Transmission electron microscopy observations reveal that microtexture of olivine dissociation products evolves from lamellar to equigranular with increasing temperature at the same pressure condition. This is in accord with the observations of synthetic samples recovered from high-pressure and high-temperature experiments. Equigranular (Mg,Fe)SiO3 Pv and Mw have 50–100 nm in diameter, and lamellar (Mg,Fe)SiO3 Pv and Mw have approximately 20 and approximately 10 nm in thickness, respectively. Partitioning coefficient, KPv/Mw = [FeO/MgO]/[FeO/MgO]Mw, between (Mg,Fe)SiO3 Pv and Mw in equigranular and lamellar textures are approximately 0.15 and approximately 0.78, respectively. The dissociation of olivine implies that the pressure and temperature conditions recorded in the shock melt vein and melt pockets during the dynamic event were approximately 25 GPa but 700 °C at least. PMID:21444781

  16. Melting Phase Relations and "Stishovite Paradox" in Lower-Mantle System MgO - FeO - SiO2 at 24 GPa

    NASA Astrophysics Data System (ADS)

    Litvin, Yuriy; Spivak, Anna; Dubrovinsky, Leonid

    2014-05-01

    Stishovite is missed in model composition of the ultrabasic lower mantle (Akaogi, 2007; Stixrude, Lithgow-Bertelloni, 2007). It is due to the fact that mineralogy of the lower mantle is estimated by experimental study of phase relation of the pyrolite composition up to 50 GPa. It was found that ultrabasic assemblage magnesiowustite+Mg-perovskite+Ca-perovskite is stable at PT-conditions of the lower mantle. However, stishovite is a representative phase in basic assemblage stishovite+Ca-perovskite+Mg-perovskite+Al-bearing resulted in similar experiments with basaltic compositions. But in this case stishovite should be subducted into the lower mantle. Meanwhile, paradoxal intergrowths of stishovite with magnesiowustite, indicatory mineral of the ultrabasic lower mantle, were found out as inclusions in 'super-deep' diamonds (Kaminsky, 2011, for review). Physicochemical reasons for in situ formation of stishovite and assemblage of stishovite and magnesiowustite ('stishovite paradox') at the primitive lower mantle were earlier discussed (Litvin et al, 2014). The discussion was based on preliminary data for melting phase relations of the lower mantle system MgO - FeO - SiO2 - Ca-perovskite. The goal of this work is experimental investigation of phase relations on the ternary MgO - FeO - SiO2 join of the lower mantle system MgO - FeO - SiO2 - CaO at pressure of 24 GPa. The sections (MgO)70(FeO)30-(SiO2)70(FeO)30 and (MgO)30(FeO)70-(SiO2)30(FeO)70of the ternary join were studied and melting phase diagrams for them constructed. Melting relations of the MgO - FeO - SiO2 join are characterized by formation of invariant peritectic point (Mg,Fe)-perovskite+(Mg,Fe)O+stishovite+L(liquid) and monovariant cotectic curve (Mg,Fe)O+stishovite+ L at compositions richer in FeO. Thus, peritectic reaction of (Mg,Fe)-perovskite and Fe-richer liquid is responsible for magnesiowustite (Mg,Fe)O + stishovite SiO2paragenesis. Origin of model primary ultrabasic magma is under control of

  17. Effect of Mg or Ag addition on the evaporation field of Al.

    PubMed

    Aruga, Yasuhiro; Nako, Hidenori; Tsuneishi, Hidemasa; Hasegawa, Yuki; Tao, Hiroaki; Ichihara, Chikara; Serizawa, Ai

    2013-09-01

    It is known that the distribution of the charge-states as well as the evaporation field shift to higher values as the specimen temperature is decreased at a constant rate of evaporation. This study has explored the effect of Mg or Ag addition on the evaporation field of Al in terms of the charge state distribution of the field evaporated Al ions. The fractional abundance of Al(2+) ions with respect to the total Al ions in Al-Mg alloy is lower than that in pure Al, whereas it shows higher level in the Al-Ag alloy at lower temperatures. The temperature dependence of the fractional abundance of Al(2+) ions has been also confirmed, suggesting that Al atoms in the Al-Mg alloy need lower evaporation field, while higher field is necessary to evaporate Al atoms in the Al-Ag alloy, compared with pure Al. This tendency is in agreement with that of the evaporation fields estimated theoretically by means of measurements of the work function and calculations of the binding energy of the pure Al, Al-Mg and Al-Ag alloys.

  18. Structure, phase composition, and strengthening of cast Al-Ca-Mg-Sc alloys

    NASA Astrophysics Data System (ADS)

    Belov, N. A.; Naumova, E. A.; Bazlova, T. A.; Alekseeva, E. V.

    2016-02-01

    The structure and phase composition of Al-Ca-Mg-Sc alloys containing 0.3 wt % Sc, up to 10 wt % Ca, and up to 10 wt % Mg have been investigated in the cast state and state after heat treatment. It has been shown that only binary phases Al4Ca, Al3Sc, and Al3Mg2 can be in equilibrium with the aluminum solid solution. It has been found that the maximum strengthening effect caused by the precipitation of Al3Sc nanoparticles for all investigated alloys is attained after annealing at 300-350°C.

  19. Ultrathin W space layer-enabled thermal stability enhancement in a perpendicular MgO/CoFeB/W/CoFeB/MgO recording frame

    PubMed Central

    Kim, Jae-Hong; Lee, Ja-Bin; An, Gwang-Guk; Yang, Seung-Mo; Chung, Woo-Seong; Park, Hae-Soo; Hong, Jin-Pyo

    2015-01-01

    Perpendicularly magnetized tunnel junctions (p-MTJs) show promise as reliable candidates for next-generation memory due to their outstanding features. However, several key challenges remain that affect CoFeB/MgO-based p-MTJ performance. One significant issue is the low thermal stability (Δ) due to the rapid perpendicular magnetic anisotropy (PMA) degradation during annealing at temperatures greater than 300 °C. Thus, the ability to provide thermally robust PMA characteristics is a key steps towards extending the use of these materials. Here, we examine the influence of a W spacer on double MgO/CoFeB/W/CoFeB/MgO frames as a generic alternative layer to ensure thermally-robust PMAs at temperatures up to 425 °C. The thickness-dependent magnetic features of the W layer were evaluated at various annealing temperatures to confirm the presence of strong ferromagnetic interlayer coupling at an optimized 0.55 nm W spacer thickness. Using this W layer we achieved a higher Δ of 78 for an approximately circular 20 nm diameter free layer device. PMID:26584638

  20. Development of a high-rate, rechargeable bipolar LiAl/FeS{sub 2} battery

    SciTech Connect

    Kaun, T.D.; Jansen, A.N.; Hash, M.C.; Prakash, J.; Turner, R.L.; Henriksen, G.L.

    1996-06-01

    Materials refinements have improved bipolar Li-Al/FeS{sub 2} batteries for power-demand applications. Current technology uses a two-phase Li-alloy cathode, LiCl-LiBr-KBr electrolyte, and an upper-plateau (UP) FeS{sub 2} anode for a battery operated at 440 C; the battery is in sealed bipolar form. The two-phase Li alloy ({alpha}+{beta} Li-Al and Li{sub 5}Al{sub 5}Fe{sub 2}) cathode provides in situ overcharge tolerance that makes the bipolar design viable. The use of LiCl-rich LiCl-LiBr-KBr electrolyte in ``electrolyte-starved`` cells achieves low-burdened cells with low area-specific impedance, with MgO powder separator. Combining dense UP FeS{sub 2} electrodes with a CuFeS{sub 2} additive and a LiI-modified electrolyte produces a stable and reversible couple, with high power capabilities. Long cycle life depends on peripheral seals for each cell in the bipolar stack. Seal composition is based on stable sulfide ceramic/sealant materials that produce strong bonds between metals and ceramics. Using these seals, bipolar Li-Al/FeS{sub 2} cells and four-cell stacks are being built and tested (25 Ah, 13-cm dia). Adding 5 mol% LiI to the electrolyte increased specific energy by 50% under a 140 W/kg, constant power C/1 rate and a 544 W/kg power pulse (8-s) schedule. Cell capacity under the high-power pulse-demand approximates the C/3 rate discharge capacity. Cell specific energy is 155 Wh/kg at the C/3 rate.

  1. Perpendicular magnetic anisotropy and magnetization dynamics in oxidized CoFeAl films.

    PubMed

    Wu, Di; Zhang, Zhe; Li, Le; Zhang, Zongzhi; Zhao, H B; Wang, J; Ma, B; Jin, Q Y

    2015-01-01

    Half-metallic Co-based full-Heusler alloys with perpendicular magnetic anisotropy (PMA), such as Co2FeAl in contact with MgO, are receiving increased attention recently due to its full spin polarization for high density memory applications. However, the PMA induced by MgO interface can only be realized for very thin magnetic layers (usually below 1.3 nm), which would have strong adverse effects on the material properties of spin polarization, Gilbert damping parameter, and magnetic stability. In order to solve this issue, we fabricated oxidized Co50Fe25Al25 (CFAO) films with proper thicknesses without employing the MgO layer. The samples show controllable PMA by tuning the oxygen pressure (PO2) and CFAO thickness (tCFAO), large perpendicular anisotropy field of ~8.0 kOe can be achieved at PO2 = 12% for the sample of tCFAO = 2.1 nm or at PO2 = 7% for tCFAO = 2.8 nm. The loss of PMA at thick tCFAO or high PO2 results mainly from the formation of large amount of CoFe oxides, which are superparamagnetic at room temperature but become hard magnetic at low temperatures. The magnetic CFAO films, with strong PMA in a relatively wide thickness range and small intrinsic damping parameter below 0.028, would find great applications in developing advanced spintronic devices. PMID:26190066

  2. Perpendicular magnetic anisotropy and magnetization dynamics in oxidized CoFeAl films.

    PubMed

    Wu, Di; Zhang, Zhe; Li, Le; Zhang, Zongzhi; Zhao, H B; Wang, J; Ma, B; Jin, Q Y

    2015-01-01

    Half-metallic Co-based full-Heusler alloys with perpendicular magnetic anisotropy (PMA), such as Co2FeAl in contact with MgO, are receiving increased attention recently due to its full spin polarization for high density memory applications. However, the PMA induced by MgO interface can only be realized for very thin magnetic layers (usually below 1.3 nm), which would have strong adverse effects on the material properties of spin polarization, Gilbert damping parameter, and magnetic stability. In order to solve this issue, we fabricated oxidized Co50Fe25Al25 (CFAO) films with proper thicknesses without employing the MgO layer. The samples show controllable PMA by tuning the oxygen pressure (PO2) and CFAO thickness (tCFAO), large perpendicular anisotropy field of ~8.0 kOe can be achieved at PO2 = 12% for the sample of tCFAO = 2.1 nm or at PO2 = 7% for tCFAO = 2.8 nm. The loss of PMA at thick tCFAO or high PO2 results mainly from the formation of large amount of CoFe oxides, which are superparamagnetic at room temperature but become hard magnetic at low temperatures. The magnetic CFAO films, with strong PMA in a relatively wide thickness range and small intrinsic damping parameter below 0.028, would find great applications in developing advanced spintronic devices.

  3. The structure of rapidly solidified Al- Fe- Cr alloys

    NASA Astrophysics Data System (ADS)

    Yearim, R.; Shechtman, D.

    1982-11-01

    Four aluminum alloys, designed for use at elevated temperatures, were studied. The alloys were supersaturated with iron and chromium, and one of them contained small amounts of Ti, V, and Zr. The starting materials were alloy powders made by the RSR (Rapid Solidification Rate) centrifugal atomization process. Extrusion bars were made from the four powders. The as-extruded microstructure and the microstructure of the alloys after annealing at 482 °C were investigated by optical and transmission electron microscopy and by X-ray diffraction. The microstructure consists of equiaxed grains of aluminum matrix and two types of precipitates, namely, Al3(Fe ,Cr) and a metastable phase, Al6(Fe,Cr). The precipitates were different in their shape, size, distribution, and location within the grains.

  4. Effect of Cr, Ti, V, and Zr Micro-additions on Microstructure and Mechanical Properties of the Al-Si-Cu-Mg Cast Alloy

    NASA Astrophysics Data System (ADS)

    Shaha, S. K.; Czerwinski, F.; Kasprzak, W.; Friedman, J.; Chen, D. L.

    2016-05-01

    Uniaxial static and cyclic tests were used to assess the role of Cr, Ti, V, and Zr additions on properties of the Al-7Si-1Cu-0.5Mg (wt pct) alloy in as-cast and T6 heat-treated conditions. The microstructure of the as-cast alloy consisted of α-Al, eutectic Si, and Cu-, Mg-, and Fe-rich phases Al2.1Cu, Al8.5Si2.4Cu, Al5.2CuMg4Si5.1, and Al14Si7.1FeMg3.3. In addition, the micro-sized Cr/Zr/Ti/V-rich phases Al10.7SiTi3.6, Al6.7Si1.2TiZr1.8, Al21.4Si3.4Ti4.7VZr1.8, Al18.5Si7.3Cr2.6V, Al7.9Si8.5Cr6.8V4.1Ti, Al6.3Si23.2FeCr9.2V1.6Ti1.3, Al92.2Si16.7Fe7.6Cr8.3V1.8, and Al8.2Si30.1Fe1.6Cr18.8V3.3Ti2.9Zr were present. During solution treatment, Cu-rich phases were completely dissolved, while the eutectic silicon, Fe-, and Cr/Zr/Ti/V-rich intermetallics experienced only partial dissolution. Micro-additions of Cr, Zr, Ti, and V positively affected the alloy strength. The modified alloy in the T6 temper during uniaxial tensile tests exhibited yield strength of 289 MPa and ultimate tensile strength of 342 MPa, being significantly higher than that for the Al-Si-Cu-Mg base. Besides, the cyclic yield stress of the modified alloy in the T6 state increased by 23 pct over that of the base alloy. The fatigue life of the modified alloy was substantially longer than that of the base alloy tested using the same parameters. The role of Cr, Ti, V, and Zr containing phases in controlling the alloy fracture during static and cyclic loading is discussed.

  5. Abnormal acoustic wave velocities in basaltic and (Fe,Al)-bearing silicate glasses at high pressures

    NASA Astrophysics Data System (ADS)

    Liu, Jin; Lin, Jung-Fu

    2014-12-01

    We have measured acoustic VP and VS velocities of (Fe,Al)-bearing MgSiO3 silicate glasses and an Icelandic basalt glass up to 25 GPa. The velocity profiles of the (Fe,Al)-bearing and basaltic silicate glasses display decreased VP and VS with minima at approximately 5 and 2 GPa, respectively, which could be explained by the mode softening in the aluminosilicate networks. Our results represent the first observation of such velocity softening extending into the chemically complex basaltic glass at a relatively low transition pressure, which is likely due to its degree of polymerization, while the Fe and Al substitutions reduce sound velocities in MgSiO3 glass. If the velocity softening in the basaltic and silicate glasses can be used as analogs for understanding melts in Earth's interior, these observations suggest that the melt fraction needed to account for the velocity reduction in the upper mantle low-velocity zone may be smaller than previously thought.

  6. Static and dynamic magnetic properties of epitaxial Co2FeAl Heusler alloy thin films

    NASA Astrophysics Data System (ADS)

    Ortiz, G.; Gabor, M. S.; Petrisor, T., Jr.; Boust, F.; Issac, F.; Tiusan, C.; Hehn, M.; Bobo, J. F.

    2011-04-01

    Structural and magnetic properties of epitaxial Co2FeAl Heusler alloy thin films were investigated. Films were deposited on single crystal MgO (001XS) substrates at room temperature, followed by an annealing process at 600 °C. MgO and Cr buffer layers were introduced in order to enhance crystalline quality, and improve magnetic properties. Structural analyses indicate that samples have grown in the B2 ordered epitaxial structure. VSM measures show that the MgO buffered sample displays a magnetization saturation of 1010 ± 30 emu/cm3, and Cr buffered sample displays a magnetization saturation of 1032 ± 40 emu/cm3. Damping factor was studied by strip-line ferromagnetic resonance measures. We observed a maximum value for the MgO buffered sample of about 8.5 × 10-3, and a minimum value of 3.8 × 10-3 for the Cr buffered one.

  7. On the cosmic evolution of Fe/Mg in QSO absorption line systems

    NASA Astrophysics Data System (ADS)

    Dey, Arjun; Torrey, Paul; Rubin, Kate H. R.; Zhu, Guangtun Ben; Suresh, Joshua

    2015-08-01

    We investigate the variation of the ratio of the equivalent widths of the Fe II λ2600 line to the Mg II λλ2796, 2803 doublet as a function of redshift in a large sample of absorption lines drawn from the Johns Hopkins University - Sloan Digital Sky Survey Absorption Line Catalog. We find that despite large scatter, the observed ratio shows a trend where the equivalent width ratio R≡ W_{Fe II}/W_{Mg II} decreases monotonically with increasing redshift z over the range 0.55 ≤ z ≤ 1.90. Selecting the subset of absorbers where the signal-to-noise ratio of the Mg II equivalent width W_{Mg II} is ≥ 3 and modelling the equivalent width ratio distribution as a Gaussian, we find that the mean of the Gaussian distribution varies as R∝ (-0.045± 0.005)z. We discuss various possible reasons for the trend. A monotonic trend in the Fe/Mg abundance ratio is predicted by a simple model where the abundances of Mg and Fe in the absorbing clouds are assumed to be the result of supernova (SN) ejecta and where the cosmic evolution in the SNIa and core-collapse SN rates is related to the cosmic star formation rate. If the trend in R reflects the evolution in the abundances, then it is consistent with the predictions of the simple model.

  8. Anatomy of electric field control of perpendicular magnetic anisotropy at Fe/MgO interfaces

    NASA Astrophysics Data System (ADS)

    Ibrahim, F.; Yang, H. X.; Hallal, A.; Dieny, B.; Chshiev, M.

    2016-01-01

    The charge-mediated effect of electric field on the perpendicular magnetic anisotropy (PMA) of Fe/MgO interfaces is investigated using first-principles calculations. We present an approach by discussing this effect in relation to the intrinsic dipole field existing at the Fe/MgO interface. A firm correlation between the PMA and the interfacial dipole is established and further verified in the absence of an applied electric field. The on-site projected PMA analysis not only elucidates that the effect of electric field on the PMA extends beyond the interfacial Fe layer, but also shows that the second Fe layer carries the largest contribution to the effect. This observation is interpreted in relation to the orbital hybridization changes induced by applying an electric field.

  9. Synthesis and characterization of Co2FeAl nanowires

    NASA Astrophysics Data System (ADS)

    Sapkota, Keshab R.; Gyawali, Parshu; Forbes, Andrew; Pegg, Ian L.; Philip, John

    2012-06-01

    We report the growth and characterization of Co2FeAl nanowires. Nanowires are grown using electrospinning method and the diameters range from 50 to 500 nm. These nanowires exhibit cubic crystal structure with a lattice constant of a =5.639 Å. The nanowires exhibit ferromagnetic behavior with a very high Curie temperature. The temperature dependent magnetization behavior displays an anomaly in the temperature range 600-850 K, which disappears at higher external magnetic fields.

  10. Native defects as sources of optical transitions in MgAl2O4 spinel

    NASA Astrophysics Data System (ADS)

    Borges, P. D.; Cott, J.; Pinto, F. G.; Tronto, J.; Scolfaro, L.

    2016-07-01

    The outstanding physical and chemical properties of the magnesium aluminate (MgAl2O4) spinel makes it an important material for novel technological applications. Considering that a presence of native defects can promote important changes in those properties, in this work we present a study of the structural, electronic and thermodynamic properties of the MgAl2O4 spinel. The calculated formation energy for isolated defects, such as the vacancies of magnesium (V Mg), aluminum (V Al) and oxygen (V O), oxygen interstitial (Oi), magnesium and aluminum antisites (MgAl, AlMg), as well as some complex defects (V O + Oi, V O + AlMg, V O + MgAl, MgAl + AlMg) in the most stable charge states are shown. Through experimental data, we obtained that complex defects centers, such as V O , V O + Oi, V O + AlMg and VO + MgAl at different charge states are good candidates for the observed optical transitions at 4.75, 5.3, and 6.4 eV. Our findings were obtained from ab initio electronic structure calculations performed by using density functional theory. The Perdew–Burke–Ernzerhof generalized gradient approximation was used for the exchange-correlation potential. Furthermore, a modified Becke-Johnson exchange potential (GGA-mBJ) correction to the exchange potential were used to obtain a suitable value for the band gap energy, 7.40 eV, in accordance with the experimental one of 7.8 eV.

  11. Native defects as sources of optical transitions in MgAl2O4 spinel

    NASA Astrophysics Data System (ADS)

    Borges, P. D.; Cott, J.; Pinto, F. G.; Tronto, J.; Scolfaro, L.

    2016-07-01

    The outstanding physical and chemical properties of the magnesium aluminate (MgAl2O4) spinel makes it an important material for novel technological applications. Considering that a presence of native defects can promote important changes in those properties, in this work we present a study of the structural, electronic and thermodynamic properties of the MgAl2O4 spinel. The calculated formation energy for isolated defects, such as the vacancies of magnesium (V Mg), aluminum (V Al) and oxygen (V O), oxygen interstitial (Oi), magnesium and aluminum antisites (MgAl, AlMg), as well as some complex defects (V O + Oi, V O + AlMg, V O + MgAl, MgAl + AlMg) in the most stable charge states are shown. Through experimental data, we obtained that complex defects centers, such as V O , V O + Oi, V O + AlMg and VO + MgAl at different charge states are good candidates for the observed optical transitions at 4.75, 5.3, and 6.4 eV. Our findings were obtained from ab initio electronic structure calculations performed by using density functional theory. The Perdew-Burke-Ernzerhof generalized gradient approximation was used for the exchange-correlation potential. Furthermore, a modified Becke-Johnson exchange potential (GGA-mBJ) correction to the exchange potential were used to obtain a suitable value for the band gap energy, 7.40 eV, in accordance with the experimental one of 7.8 eV.

  12. Al-Cu-Li and Al-Mg-Li alloys: Phase composition, texture, and anisotropy of mechanical properties (Review)

    NASA Astrophysics Data System (ADS)

    Betsofen, S. Ya.; Antipov, V. V.; Knyazev, M. I.

    2016-04-01

    The results of studying the phase transformations, the texture formation, and the anisotropy of the mechanical properties in Al-Cu-Li and Al-Mg-Li alloys are generalized. A technique and equations are developed to calculate the amounts of the S1 (Al2MgLi), T1 (Al2CuLi), and δ' (Al3Li) phases. The fraction of the δ' phase in Al-Cu-Li alloys is shown to be significantly higher than in Al-Mg-Li alloys. Therefore, the role of the T1 phase in the hardening of Al-Cu-Li alloys is thought to be overestimated, especially in alloys with more than 1.5% Li. A new model is proposed to describe the hardening of Al-Cu-Li alloys upon aging, and the results obtained with this model agree well with the experimental data. A texture, which is analogous to that in aluminum alloys, is shown to form in sheets semiproducts made of Al-Cu-Li and Al-Mg-Li alloys. The more pronounced anisotropy of the properties of lithium-containing aluminum alloys is caused by a significant fraction of the ordered coherent δ' phase, the deformation mechanism in which differs radically from that in the solid solution.

  13. Melting and casting of FeAl-based cast alloy

    SciTech Connect

    Sikka, V.K.; Wilkening, D.; Liebetrau, J.; Mackey, B.

    1998-11-01

    The FeAl-based intermetallic alloys are of great interest because of their low density, low raw material cost, and excellent resistance to high-temperature oxidation, sulfidation, carburization, and molten salts. The applications based on these unique properties of FeAl require methods to melt and cast these alloys into complex-shaped castings and centrifugal cast tubes. This paper addresses the melting-related issues and the effect of chemistry on the microstructure and hardness of castings. It is concluded that the use of the Exo-Melt{trademark} process for melting and the proper selection of the aluminum melt stock can result in porosity-free castings. The FeAl alloys can be melted and cast from the virgin and revert stock. A large variation in carbon content of the alloys is possible before the precipitation of graphite flakes occurs. Titanium is a very potent addition to refine the grain size of castings. A range of complex sand castings and two different sizes of centrifugal cast tubes of the alloy have already been cast.

  14. Towards a Superplastic Forming of Fe-Mn-Al Alloys

    SciTech Connect

    Guanabara, Paulo Jr.; Bueno, Levi de O.; Ferreira Batalha, Gilmar

    2011-01-17

    The aim is to study the characteristics of superplasticity, mostly on non qualified materials, such as austenitic steel of the Fe-Mn-Al alloy, which has some of the specific material parameters closely related to microstructural mechanisms. These parameters are used as indicators of material superplastic potentiality. The material was submitted to hot tensile testing, within a temperature range from 600 deg. C to 1000 deg. C and strain-rates varying from 10{sup -6} to 1 s{sup -1}. The strain rate sensitivity parameter (m) and observed maximum elongation until rupture ({epsilon}{sub r}) could be determined and also obtained from the hot tensile test. The experiments stated a possibility of superplastic behaviour in a Fe-Mn-Al alloy within a temperature range from 700 deg. C to 900 deg. C with grain size around 3 {mu}m (ASTM grain size 12) and average strain rate sensitivity of m {approx} 0.54, as well as a maximum elongation at rupture around 600%. The results are based on a more enhanced research from the authors; however, this paper has focused just on the hot tensile test, as further creep tests results are not available herein. There are rare examples of superplasticity study of an austenitic steel Fe-Mn-Al alloy, thus this work showed some possibility of exploring the potential use of such materials in this regime at temperatures {>=}700 deg. C.

  15. Tunnel anisotropic magnetoresistance in CoFeB|MgO|Ta junctions

    SciTech Connect

    Hatanaka, S.; Miwa, S. Matsuda, K.; Nawaoka, K.; Tanaka, K.; Morishita, H.; Goto, M.; Mizuochi, N.; Shinjo, T.; Suzuki, Y.

    2015-08-24

    We found that CoFeB|MgO|Ta tunnel junctions exhibit tunnel anisotropic magnetoresistance (TAMR) at room temperature. The tunnel junctions exhibit positive magnetoresistance with the application of a magnetic field normal to the film plane. The dependencies on the applied magnetic field angle and MgO thickness reveal that the magnetoresistance originates from the TAMR, caused by the spin polarization and the spin-orbit interaction at the CoFeB|MgO interface. We also found that the TAMR can be used to detect ferromagnetic resonance in the CoFeB. This detection method could be useful for the characterization of nanomagnets that are free from the spin-transfer effect and the stray field of a reference layer, unlike conventional magnetic tunnel junctions.

  16. Effect of chlorine on near-liquidus phase equilibria of an Fe-Mg-rich tholeiitic basalt

    NASA Astrophysics Data System (ADS)

    Filiberto, Justin; Dasgupta, Rajdeep; Gross, Juliane; Treiman, Allan H.

    2014-07-01

    The importance of Cl in basalt petrogenesis has been recognized, yet constraints on its effect on liquidus crystallization of basalts are scarce. In order to quantify the role of Cl in basaltic systems, we have experimentally determined near-liquidus phase relations of a synthetic Fe-Mg-rich basalt, doped with 0.0-2.5 wt% dissolved Cl, at 0.7, 1.1, and 1.5 GPa. Results have been parameterized and compared with previous data from literature. The effect of Cl on mineral chemistry and liquidus depression is dependent on the starting basaltic composition. The liquidus depression measured for a SiO2-rich, Al2O3-poor basalt is smaller than that observed for a basaltic melt depleted in silica and enriched in FeOT and Al2O3. The effect of Cl on depression of the olivine-orthopyroxene-liquid multiple saturation pressure does not seem to vary with the starting composition of the basaltic liquid. This suggests that Cl may significantly promote the generation of silica-poor, Fe-Al-rich magmas in the Earth, Mars, and the Moon.

  17. Al-matrix composite materials reinforced by Al-Cu-Fe particles

    NASA Astrophysics Data System (ADS)

    Bonneville, J.; Laplanche, G.; Joulain, A.; Gauthier-Brunet, V.; Dubois, S.

    2010-07-01

    Al-matrix material composites were produced using hot isostatic pressing technique, starting with pure Al and icosahedral (i) Al-Cu-Fe powders. Depending on the processing temperature, the final reinforcement particles are either still of the initial i-phase or transformed into the tetragonal ω-Al00.70Cu0.20Fe0.10 crystalline phase. Compression tests performed in the temperature range 293K - 823K on the two types of composite, i.e. Al/i and Al/ω, indicate that the flow stress of both composites is strongly temperature dependent and exhibit distinct regimes with increasing temperature. Differences exist between the two composites, in particul ar in yield stress values. In the low temperatureregime (T <= 570K), the yield stress of the Al/ω composite is nearly 75% higher than that of the Al/i composite, while for T > 570K both composites exhibit similar yield stress values. The results are interpreted in terms of load transfer contribution between the matrix and the reinforcement particles and elementary dislocation mechanisms in the Al matrix.

  18. Formation of "Chemically Pure" Magnetite from Mg-Fe-Carbonates Implications for the Exclusively Inorganic Origin of Magnetite and Sulfides in Martian Meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Golden, D. C.; Ming, Douglas W.; Lauer, H. V., Jr.; Morris, R. V.; Trieman, A. H.; McKay, G. A.

    2006-01-01

    Magnetite and sulfides in the black rims of carbonate globules in Martian meteorite ALH84001 have been studied extensively because of the claim by McKay et al. that they are biogenic in origin. However, exclusively inorganic (abiotic) processes are able to account for the occurrence of carbonate-sulfide-magnetite assemblages in the meteorite. We have previously precipitated chemically zoned and sulfide-bearing carbonate globules analogous to those in ALH84001 (at less than or equal to 150 C) from multiple fluxes of variable-composition Ca-Mg-Fe-CO2-S-H2O solutions. Brief heating of precipitated globules to approx. 470 C produced magnetite and pyrrhotite within the globules by thermal decomposition of siderite and pyrite, respectively. We have also shown that morphology of magnetite formed by inorganic thermal decomposition of Fe-rich carbonate is similar to the morphology of so-called biogenic magnetite in the carbonate globules of ALH84001. Magnetite crystals in the rims of carbonate globules in ALH84001 are chemically pure [Note: "Chemically pure" is defined here as magnetite with Mg at levels comparable or lower than Mg detected by [8] in ALH84001 magnetite]. A debate continues on whether or not chemically pure magnetite can form by the thermal decomposition of mixed Mg-Fe-carbonates that have formed under abiotic conditions. Thomas-Keprta et al. argue that it is not possible to form Mg-free magnetite from Mg-Fe-carbonate based on thermodynamic data. We previously suggested that chemically pure magnetite could form by the thermal decomposition of relatively pure siderite in the outer rims of the globules. Mg-Fe-carbonates may also thermally decompose under conditions conducive for formation of chemically pure magnetite. In this paper we show through laboratory experiments that chemically pure magnetite can form by an inorganic process from mixed Mg-Fe-carbonates.

  19. Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures

    PubMed Central

    Peng, Shouzhong; Wang, Mengxing; Yang, Hongxin; Zeng, Lang; Nan, Jiang; Zhou, Jiaqi; Zhang, Youguang; Hallal, Ali; Chshiev, Mairbek; Wang, Kang L.; Zhang, Qianfan; Zhao, Weisheng

    2015-01-01

    Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts extensive attentions due to its non-volatility, high density and low power consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well as a large value of perpendicular magnetic anisotropy (PMA). It has been experimentally proven that a capping layer coating on CoFeB layer is essential to obtain a strong PMA. However, the physical mechanism of such effect remains unclear. In this paper, we investigate the origin of the PMA in MgO/CoFe/metallic capping layer structures by using a first-principles computation scheme. The trend of PMA variation with different capping materials agrees well with experimental results. We find that interfacial PMA in the three-layer structures comes from both the MgO/CoFe and CoFe/capping layer interfaces, which can be analyzed separately. Furthermore, the PMAs in the CoFe/capping layer interfaces are analyzed through resolving the magnetic anisotropy energy by layer and orbital. The variation of PMA with different capping materials is attributed to the different hybridizations of both d and p orbitals via spin-orbit coupling. This work can significantly benefit the research and development of nanoscale STT-MRAM. PMID:26656721

  20. Exchange bias effects in Heusler alloy Ni2MnAl/Fe bilayers

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Tomoki; Kubota, Takahide; Sugiyama, Tomoko; Huminiuc, Teodor; Hirohata, Atsufumi; Takanashi, Koki

    2016-06-01

    Ni2MnAl Heusler alloy thin films were epitaxially grown on MgO(1 0 0) single crystal substrates by ultra-high-vacuum magnetron sputtering technique. X-ray diffraction and transmission electron microscopy observation revealed that the structures of all the Ni2MnAl thin films were B2-ordered regardless of the deposition temperature ranging from room temperature to 600 °C. The temperature dependence of electrical resistivity showed a kink about 280 K, which was consistent with a reported value of the Néel temperature for antiferromagnetic B2-Ni2MnAl. The magnetization curves of Ni2MnAl/Fe bilayer samples showed a shift caused by the interfacial exchange interaction at 10 K. The maximum value of the exchange bias field H ex was 55 Oe corresponding to the exchange coupling energy J k of 0.03 erg cm-2.

  1. Moessbauer spectroscopy of Mg(0.9)Fe(0.1)SiO3 perovskite

    NASA Technical Reports Server (NTRS)

    Jeanloz, Raymond; O'Neill, Bridget; Pasternak, Moshe P.; Taylor, R. D.; Bohlen, Steven R.

    1992-01-01

    Ambient pressure Moessbauer spectra of Mg(0.9)Fe-57(0.1)SiO3 perovskite synthesized at pressure-temperature conditions of about 50 GPa and 1700 K show that the iron is entirely high-spin Fe(2+) and appears to be primarily located in the octahedral site within the crystal structure. We observe broad Moessbauer lines, suggesting a distribution of electric-field gradients caused by disorder associated with the Fe ions. Also, the perovskite exhibits magnetic ordering at temperatures lower than 5 K, implying that there is a magnetic contribution to the absolute ('third-law') entropy of this phase.

  2. The Formation of Fe/Mg Smectite Under Mildly Acidic Conditions on Early Mars

    NASA Technical Reports Server (NTRS)

    Sutter, Brad; Golden, D. C.; Ming, Douglas W.; Niles, P. B.

    2011-01-01

    The detection of Fe/Mg smectites and carbonate in Noachian and early Hesperian terrain of Mars has been used to suggest that neutral to mildly alkaline conditions prevailed during the early history of Mars. However, if early Mars was neutral to moderately alkaline with a denser CO2 atmosphere than today, then large carbonates deposits should be more widely detected in Noachian terrain. The critical question is: Why have so few carbonate deposits been detected compared to Fe/Mg smectites? We suggest that Fe/Mg smectites on early Mars formed under mildly acidic conditions, which would inhibit the extensive formation of carbonate deposits. The goal of this work is to evaluate the formation of Fe/Mg smectites under mildly acidic conditions. The stability of smectites under mildly acidic conditions is attributed to elevated Fe/Mg activities that inhibit smectite dissolution. Beidelite and saponite have been shown to form from hydrothermal alteration of basaltic glass at pH 3.5-4.0 in seawater solutions. Nontronite is also known to be stable in mildly acidic systems associated with mafic and ultramafic rock. Nontronite was shown to form in acid sulfate soils in the Bangkok Plain, Thailand due to oxidation of Fe-sulfides that transformed saponite to nontronite. Smectite is known to transform to kaolinite in naturally acid soils due to selective leaching of Mg. However, if Mg removal is limited, then based on equilibrium relationships, the dissolution of smectite should be minimized. If Fe and Mg solution activities are sufficiently high, such as might be found in a low water/rock ratio system that is poorly drained, smectite could form and remain stable under mildly acidic conditions on Mars. The sources of mild acidity on early Mars includes elevated atmospheric CO2 levels, Fe-hydrolysis reactions, and the presence of volcanic SO2 aerosols. Equilibrium calculations dictate that water equilibrated with an early Mars CO2 atmosphere at 1 to 4 bar yields a pH of 3.6 to 3

  3. The Formation of Fe/Mg Smectite Under Mildly Acidic Conditions on Early Mars

    NASA Astrophysics Data System (ADS)

    Sutter, B.; Golden, D. C.; Ming, D.; Niles, P. B.

    2011-12-01

    The detection of Fe/Mg smectites and carbonate in Noachian and early Hesperian terrain of Mars has been used to suggest that neutral to mildly alkaline conditions prevailed during the early history of Mars. However, if early Mars was neutral to moderately alkaline with a denser CO2 atmosphere than today, then "large" carbonates deposits should be more widely detected in Noachian terrain. The critical question is: Why have so few carbonate deposits been detected compared to Fe/Mg smectites? We suggest that Fe/Mg smectites on early Mars formed under mildly acidic conditions, which would inhibit the extensive formation of carbonate deposits. The goal of this work is to evaluate the formation of Fe/Mg smectites under mildly acidic conditions. The stability of smectites under mildly acidic conditions is attributed to elevated Fe/Mg activities that inhibit smectite dissolution. Beidelite and saponite have been shown to form from hydrothermal alteration of basaltic glass at pH 3.5-4.0 in seawater solutions. Nontronite is also known to be stable in mildly acidic systems associated with mafic and ultramafic rock. Nontronite was shown to form in acid sulfate soils in the Bangkok Plain, Thailand due to oxidation of Fe-sulfides that transformed saponite to nontronite. Smectite is known to transform to kaolinite in naturally acid soils due to selective leaching of Mg. However, if Mg removal is limited, then based on equilibrium relationships, the dissolution of smectite should be minimized. If Fe and Mg solution activities are sufficiently high, such as might be found in a low water/rock ratio system that is poorly drained, smectite could form and remain stable under mildly acidic conditions on Mars. The sources of mild acidity on early Mars includes elevated atmospheric CO2 levels, Fe-hydrolysis reactions, and the presence of volcanic SO2 aerosols. Equilibrium calculations dictate that water equilibrated with an early Mars CO2 atmosphere at 1 to 4 bar yields a pH of 3.6 to 3

  4. TL and OSL studies of carbon doped magnesium aluminate (MgAl2O4:C)

    NASA Astrophysics Data System (ADS)

    Raj, Sanu S.; Mishra, D. R.; Soni, Anuj; Grover, V.; Polymeris, G. S.; Muthe, K. P.; Jha, S. K.; Tyagi, A. K.

    2016-10-01

    The MgAl2O4:C has been synthesized by using two different methods by electron gun and vacuum assisted melting of MgAl2O4 in presence of graphite. The MgAl2O4:C phosphor thus developed by these two different methods have similar types of the TL/OSL defects with multiple overlapping TL glow peaks from 100 °C to 400 °C. The Computerized Curve De-convolution Analysis (CCDA) has been used to measure TL parameters such as thermal trap depth, frequency factor and order of kinetic associated with charge transfer process in TL phenomenon. The investigated TL/OSL results show that these two methods of incorporating carbon in MgAl2O4 have generated closely resemble the defects of similar types in MgAl2O4:C lattice. However, the MgAl2O4:C synthesized by electron gun shows relatively larger concentration of the TL/OSL defects as compared to MgAl2O4:C synthesized using vacuum assisted melting method. The photo-ionization cross-section (PIC) associated with fastest OSL component of MgAl2O4: C is found to be ∼ 0.5 times than that of fastest OSL component of commercially available dosimetric grade α-Al2O3:C. The MgAl2O4:C thus developed shows good dynamic OSL dose linearity from few mGy to 1 Gy. This work reveals that MgAl2O4:C could be developed as potential tissue equivalent OSL / TL material.

  5. FeAl and NbAl3 Intermetallic-HVOF Coatings: Structure and Properties

    NASA Astrophysics Data System (ADS)

    Guilemany, J. M.; Cinca, N.; Dosta, S.; Cano, I. G.

    2009-12-01

    Transition metal aluminides in their coating form are currently being explored in terms of resistance to oxidation and mechanical behavior. This interest in transition metal aluminides is mainly due to the fact that their high Al content makes them attractive for high-temperature applications. This is also a reason to study their resistance to wear; they may be suitable for use in applications that produce a lot of wear in aggressive environments, thus replacing established coating materials. In this study, the microstructure, microhardness, and wear and oxidation performance of FeAl and NbAl3 coatings produced by high-velocity oxy-fuel spraying are evaluated with two main aims: (i) to compare these two coating systems—a commonly studied aluminide (FeAl) and, NbAl3, an aluminide whose deposition by thermal spraying has not been attempted to date—and (ii) to analyze the relationship between their microstructure, composition and properties, and so clarify their wear and oxidation mechanisms. In the present study, the higher hardness of niobium aluminide coatings did not correlate with a higher wear resistance and, finally, although pesting phenomena (disintegration in oxidizing environments) were already known of in bulk niobium aluminides, here their behavior in the coating form is examined. It was shown that such accelerated oxidation was inevitable with respect to the better resistance of FeAl, but further improvements are foreseen by addition of alloying elements in that alloy.

  6. Novel strip-cast Mg/Al clad sheets with excellent tensile and interfacial bonding properties

    PubMed Central

    Kim, Jung-Su; Lee, Dong Ho; Jung, Seung-Pill; Lee, Kwang Seok; Kim, Ki Jong; Kim, Hyoung Seop; Lee, Byeong-Joo; Chang, Young Won; Yuh, Junhan; Lee, Sunghak

    2016-01-01

    In order to broaden industrial applications of Mg alloys, as lightest-weight metal alloys in practical uses, many efforts have been dedicated to manufacture various clad sheets which can complement inherent shortcomings of Mg alloys. Here, we present a new fabrication method of Mg/Al clad sheets by bonding thin Al alloy sheet on to Mg alloy melt during strip casting. In the as-strip-cast Mg/Al clad sheet, homogeneously distributed equi-axed dendrites existed in the Mg alloy side, and two types of thin reaction layers, i.e., γ (Mg17Al12) and β (Mg2Al3) phases, were formed along the Mg/Al interface. After post-treatments (homogenization, warm rolling, and annealing), the interfacial layers were deformed in a sawtooth shape by forming deformation bands in the Mg alloy and interfacial layers, which favorably led to dramatic improvement in tensile and interfacial bonding properties. This work presents new applications to multi-functional lightweight alloy sheets requiring excellent formability, surface quality, and corrosion resistance as well as tensile and interfacial bonding properties. PMID:27245687

  7. Novel strip-cast Mg/Al clad sheets with excellent tensile and interfacial bonding properties

    NASA Astrophysics Data System (ADS)

    Kim, Jung-Su; Lee, Dong Ho; Jung, Seung-Pill; Lee, Kwang Seok; Kim, Ki Jong; Kim, Hyoung Seop; Lee, Byeong-Joo; Chang, Young Won; Yuh, Junhan; Lee, Sunghak

    2016-06-01

    In order to broaden industrial applications of Mg alloys, as lightest-weight metal alloys in practical uses, many efforts have been dedicated to manufacture various clad sheets which can complement inherent shortcomings of Mg alloys. Here, we present a new fabrication method of Mg/Al clad sheets by bonding thin Al alloy sheet on to Mg alloy melt during strip casting. In the as-strip-cast Mg/Al clad sheet, homogeneously distributed equi-axed dendrites existed in the Mg alloy side, and two types of thin reaction layers, i.e., γ (Mg17Al12) and β (Mg2Al3) phases, were formed along the Mg/Al interface. After post-treatments (homogenization, warm rolling, and annealing), the interfacial layers were deformed in a sawtooth shape by forming deformation bands in the Mg alloy and interfacial layers, which favorably led to dramatic improvement in tensile and interfacial bonding properties. This work presents new applications to multi-functional lightweight alloy sheets requiring excellent formability, surface quality, and corrosion resistance as well as tensile and interfacial bonding properties.

  8. Novel strip-cast Mg/Al clad sheets with excellent tensile and interfacial bonding properties.

    PubMed

    Kim, Jung-Su; Lee, Dong Ho; Jung, Seung-Pill; Lee, Kwang Seok; Kim, Ki Jong; Kim, Hyoung Seop; Lee, Byeong-Joo; Chang, Young Won; Yuh, Junhan; Lee, Sunghak

    2016-01-01

    In order to broaden industrial applications of Mg alloys, as lightest-weight metal alloys in practical uses, many efforts have been dedicated to manufacture various clad sheets which can complement inherent shortcomings of Mg alloys. Here, we present a new fabrication method of Mg/Al clad sheets by bonding thin Al alloy sheet on to Mg alloy melt during strip casting. In the as-strip-cast Mg/Al clad sheet, homogeneously distributed equi-axed dendrites existed in the Mg alloy side, and two types of thin reaction layers, i.e., γ (Mg17Al12) and β (Mg2Al3) phases, were formed along the Mg/Al interface. After post-treatments (homogenization, warm rolling, and annealing), the interfacial layers were deformed in a sawtooth shape by forming deformation bands in the Mg alloy and interfacial layers, which favorably led to dramatic improvement in tensile and interfacial bonding properties. This work presents new applications to multi-functional lightweight alloy sheets requiring excellent formability, surface quality, and corrosion resistance as well as tensile and interfacial bonding properties.

  9. Novel strip-cast Mg/Al clad sheets with excellent tensile and interfacial bonding properties.

    PubMed

    Kim, Jung-Su; Lee, Dong Ho; Jung, Seung-Pill; Lee, Kwang Seok; Kim, Ki Jong; Kim, Hyoung Seop; Lee, Byeong-Joo; Chang, Young Won; Yuh, Junhan; Lee, Sunghak

    2016-01-01

    In order to broaden industrial applications of Mg alloys, as lightest-weight metal alloys in practical uses, many efforts have been dedicated to manufacture various clad sheets which can complement inherent shortcomings of Mg alloys. Here, we present a new fabrication method of Mg/Al clad sheets by bonding thin Al alloy sheet on to Mg alloy melt during strip casting. In the as-strip-cast Mg/Al clad sheet, homogeneously distributed equi-axed dendrites existed in the Mg alloy side, and two types of thin reaction layers, i.e., γ (Mg17Al12) and β (Mg2Al3) phases, were formed along the Mg/Al interface. After post-treatments (homogenization, warm rolling, and annealing), the interfacial layers were deformed in a sawtooth shape by forming deformation bands in the Mg alloy and interfacial layers, which favorably led to dramatic improvement in tensile and interfacial bonding properties. This work presents new applications to multi-functional lightweight alloy sheets requiring excellent formability, surface quality, and corrosion resistance as well as tensile and interfacial bonding properties. PMID:27245687

  10. Synthesis of Mg-Al and Zn-Al-layered double hydroxide nanocrystals using laser ablation in water

    SciTech Connect

    Hur, Tae-Bong; Phuoc, Tran X.; Chyu, Minking K.

    2009-06-01

    In this paper, we report our results on the synthesis of Mg-Al and Zn-Al-layered double hydroxides using the laser ablation in the liquid technique. To prepare these layered double hydroxides (LDH) we first began with the laser generation of a Mg (or zinc) target submerged in deionized water and then ablated an aluminum target submerged in the previously prepared Mg-deionized water suspensions (Mg-dw) to produce Mg-Al LDH and in Zn-dw to prepare Zn-Al LDH. In these ablation tests, the Mg ablation duration was selected to vary from 5 to 60 min, while the Al ablation duration was kept constant at 30 min for all samples. The generated Mg-Al LDH was a gel-like and well crystallized nanoparticles of a rod-like shape and were arranged in a well-organized pattern. When the Mg ablation duration between 25 and 35 min, the synthesized nanocrystals were stoichiometric with a formula of Mg6Al2(OH)(18)4.5 (H2O), the interlayer distance (d((0 0 3))-spacing) was 7.8 angstrom and the average grain size was 8.0 nm. The synthesized Zn-Al LDH revealed various lamellar thin plate-like nanostructures of hexagonal morphologies. The average diameters of these structures was about 500 nm and the thickness of a single layer was approximately about 6.0 nm. The XRD diffraction peaks were indexed in hexagonal lattice with a(o) = 3.07 angstrom and c(o) = 15.12 angstrom. These indexes were (002), (004), and (008) and the corresponding interlayer distances, d-spacing (angstrom), were 7.56 (002), 3.782 (004), and 1.891 (008), respectively.

  11. Thermoelectric properties of Al-doped Mg2Si thin films deposited by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Chen, Zhi-jian; Zhou, Bai-yang; Li, Jian-xin; Wen, Cui-lian

    2016-11-01

    The Al-doped Mg2Si thin films were fabricated by two-target alternative magnetron sputtering technique, and the influences of different Al doping contents on the thermoelectric properties of Al-doped Mg2Si thin films were investigated. The compositions, crystal structures, electronic transport properties and thermoelectric properties of the thin films were examined using energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Hall coefficient measurement and Seebeck coefficient measurement system, respectively. The EDS results show that the thin films doped with Al target sputtering power of 30 W, 60 W and 90 W have the Al content of 0.68 at.%, 1.56 at.% and 2.85 at.%, respectively. XRD results indicate that the diffraction peaks of Mg2Si become stronger with increasing Al dopant. The results of Hall coefficient measurement and Seebeck coefficient measurement system reveal that all the samples are n-type. The conductivities of Al-doped Mg2Si thin films are significantly greater than that of undoped Mg2Si thin film, and increase with increasing Al doping content. With the increase of temperature, the absolute value of the Seebeck coefficients of Mg2Si base thin films increase firstly and then decrease. The maximum power factor obtained is 3.8 mW m-1 k-2 for 1.56 at.% Al-doped Mg2Si thin film at 573 K.

  12. Tunneling magnetoresistance in Fe{sub 3}Si/MgO/Fe{sub 3}Si(001) magnetic tunnel junctions

    SciTech Connect

    Tao, L. L.; Liang, S. H.; Liu, D. P.; Wei, H. X.; Han, X. F.; Wang, Jian

    2014-04-28

    We present a theoretical study of the tunneling magnetoresistance (TMR) and spin-polarized transport in Fe{sub 3}Si/MgO/Fe{sub 3}Si(001) magnetic tunnel junction (MTJ). It is found that the spin-polarized conductance and bias-dependent TMR ratios are rather sensitive to the structure of Fe{sub 3}Si electrode. From the symmetry analysis of the band structures, we found that there is no spin-polarized Δ{sub 1} symmetry bands crossing the Fermi level for the cubic Fe{sub 3}Si. In contrast, the tetragonal Fe{sub 3}Si driven by in-plane strain reveals half-metal nature in terms of Δ{sub 1} state. The giant TMR ratios are predicted for both MTJs with cubic and tetragonal Fe{sub 3}Si electrodes under zero bias. However, the giant TMR ratio resulting from interface resonant transmission for the former decreases rapidly with the bias. For the latter, the giant TMR ratio can maintain up to larger bias due to coherent transmission through the majority-spin Δ{sub 1} channel.

  13. Microstructure and magnetic properties of FeCo epitaxial thin films grown on MgO single-crystal substrates

    SciTech Connect

    Shikada, Kouhei; Ohtake, Mitsuru; Futamoto, Masaaki; Kirino, Fumiyoshi

    2009-04-01

    FeCo epitaxial films were prepared on MgO(100), MgO(110), and MgO(111) substrates by ultrahigh vacuum molecular beam epitaxy. FeCo thin films with (100), (211), and (110) planes parallel to the substrate surface grow on respective MgO substrates. FeCo/MgO interface structures are studied by high-resolution cross-sectional transmission electron microscopy and the epitaxial growth mechanism is discussed. Atomically sharp boundaries are recognized between the FeCo thin films and the MgO substrates where misfit dislocations are introduced in the FeCo thin films presumably to decrease the lattice misfits. Misfit dislocations are observed approximately every 9 and 1.4 nm in FeCo thin film at the FeCo/MgO(100) and the FeCo/MgO(110) interfaces, respectively. X-ray diffraction analysis indicates that the lattice spacing measured parallel to the single-crystal substrate surfaces are in agreement within 0.1% with those of the respective bulk values of Fe{sub 50}Co{sub 50} alloy crystal, showing that the FeCo film strain is very small. The magnetic anisotropies of these epitaxial films basically reflect the magnetocrystalline anisotropy of bulk FeCo alloy crystal.

  14. Formation of Fe/mg Smectite Under Acidic Conditions from Synthetic Adirondack Basaltic Glass: an Analog to Fe/mg Smectite Formation on Mars

    NASA Technical Reports Server (NTRS)

    Sutter, B.; Peretyazhko, T.; Morris, R. V.; Ming, D. W.

    2014-01-01

    Smectite has been detected as layered material hundreds of meters thick, in intracrater depositional fans, in plains sediments, and deposits at depth on Mars. If early Mars hosted a dense CO2 atmosphere, then extensive carbonate should have formed in the neutral/alkaline conditions expected for smectite formation. However, large carbonate deposits on Mars have not been discovered. Instead of neutral to moderately alkaline conditions, early Mars may have experienced mildly acidic conditions that allowed for Fe/Mg smectite formation but prevented widespread carbonate formation. The objective of this work is to demonstrate that Fe(II)/Mg saponite and nontronite can form in mildly acidic solutions (e.g., pH 4). Synthetic basaltic glass (< 53 microns) of Adirondack rock class composition was exposed to pH 4 (acetic acid buffer) and N2 purged (anoxic) solutions amended with 0 and 10 mM Mg or Fe(II). Basaltic glass in these solutions was heated to 200 C in batch reactors for 1, 7, and 14 days. X-ray diffraction analysis of reacted materials detected the presence of phyllosilicates as indicated by a approx. 15.03-15.23Angstroms (001) peak. Smectite was confirmed as the phyllosilicate after treatments with glycerol and KCl and heating to 550 C. Trioctahedral saponite was confirmed by the presence of a 4.58 to 4.63 Angstroms (02l) and 1.54Angstroms (060) peaks. Saponite concentration was highest, as indicated by XRD peak intensity, in the 10 mM Mg treatment followed by the 0 mM and then 10 mM Fe(II) treatments. This order of sapontite concentration suggests that Fe(II) additions may have a role in slowing the kinetics of saponite formation relative to the other treatments. Nontronite synthesis was attempted by exposing Adirondack basaltic glass to pH 4 oxic solutions (without N2 purge) at 200 C for 14 days. X-ray diffraction analysis indicated that mixtures of trioctahedral (saponite) and dioctahedral (nontronite) may have formed in these experiments based on the 02l and 060

  15. Formation of Fe/Mg Smectite under acidic conditions from synthetic Adirondack Basaltic Glass: An Analog to Fe/Mg Smectite Formation on Mars.

    NASA Astrophysics Data System (ADS)

    Sutter, B.; Peretyazhko, T.; Morris, R. V.; Ming, D. W.

    2014-12-01

    Smectite has been detected as layered material hundreds of meters thick, in intracrater depositional fans, in plains sediments, and deposits at depth on Mars. If early Mars hosted a dense CO2 atmosphere, then extensive carbonate should have formed in the neutral/alkaline conditions expected for smectite formation. However, large carbonate deposits on Mars have not been discovered. Instead of neutral to moderately alkaline conditions, early Mars may have experienced mildly acidic conditions that allowed for Fe/Mg smectite formation but prevented widespread carbonate formation. The objective of this work is to demonstrate that Fe(II)/Mg-saponite and nontronite can form in mildly acidic solutions (e.g., pH 4). Synthetic basaltic glass (< 53 μm) of Adirondack rock class composition was exposed to pH 4 (acetic acid buffer) and N2 purged (anoxic) solutions amended with 0 and 10 mM Mg or Fe(II). Basaltic glass in these solutions was heated to 200ºC in batch reactors for 1, 7, and 14 days. X-ray diffraction analysis of reacted materials detected the presence of phyllosilicates as indicated by a ~15.03-15.23Ǻ (001) peak. Smectite was confirmed as the phyllosilicate after treatments with glycerol and KCl and heating to 550°C. Trioctahedral saponite was confirmed by the presence of a 4.58 to 4.63 Ǻ (02l) and 1.54Ǻ (060) peaks. Saponite concentration was highest, as indicated by XRD peak intensity, in the 10 mM Mg treatment followed by the 0 mM and then 10 mM Fe(II) treatments. This order of sapontite concentration suggests that Fe(II) additions may have a role in slowing the kinetics of saponite formation relative to the other treatments. Nontronite synthesis was attempted by exposing Adirondack basaltic glass to pH 4 oxic solutions (without N2 purge) at 200ºC for 14 days. X-ray diffraction analysis indicated that mixtures of trioctahedral (saponite) and dioctahedral (nontronite) may have formed in these experiments based on the 02l and 060 peaks. Mössbauer analysis

  16. Microstructural Evolution and Solidification Behavior of Al-Mg-Si Alloy in High-Pressure Die Casting

    NASA Astrophysics Data System (ADS)

    Ji, Shouxun; Wang, Yun; Watson, D.; Fan, Z.

    2013-07-01

    Microstructural evolution and solidification behavior of Al-5 wt pct Mg-1.5 wt pct Si-0.6 wt pct Mn-0.2 wt pct Ti alloy have been investigated using high-pressure die casting. Solidification commences with the formation of primary α-Al phase in the shot sleeve and is completed in the die cavity. The average size of dendrites and fragmented dendrites of the primary α-Al phase formed in the shot sleeve is 43 μm, and the globular primary α-Al grains formed inside the die cavity is at a size of 7.5 μm. Solidification inside the die cavity also forms the lamellar Al-Mg2Si eutectic phase and the Fe-rich intermetallics. The size of the eutectic cells is about 10 μm, in which the lamellar α-Al phase is 0.41 μm thick. The Fe-rich intermetallic compound exhibits a compact morphology and is less than 2 μm with a composition of 1.62 at. pct Si, 3.94 at. pct Fe, and 2.31 at. pct Mn. A solute-enriched circular band is always observed parallel to the surface of the casting. The band zone separates the outer skin region from the central region of the casting. The solute concentration is consistent in the skin region and shows a general drop toward the center inside the band for Mg and Si. The peak of the solute enrichment in the band zone is much higher than the nominal composition of the alloy. The die casting exhibits a combination of brittle and ductile fracture. There is no significant difference on the fracture morphology in the three regions. The band zone is not significantly detrimental in terms of the fracture mechanism in the die casting. Calculations using the Mullins and Sekerka stability criterion reveal that the solidification of the primary α-Al phase inside the die cavity has been completed before the spherical α-Al globules begin to lose their stability, but the α-Al grains formed in the shot sleeve exceed the limit of spherical growth and therefore exhibit a dendritic morphology.

  17. Fabrication of Spherical AlSi10Mg Powders by Radio Frequency Plasma Spheroidization

    NASA Astrophysics Data System (ADS)

    Wang, Linzhi; Liu, Ying; Chang, Sen

    2016-05-01

    Spherical AlSi10Mg powders were prepared by radio frequency plasma spheroidization from commercial AlSi10Mg powders. The fabrication process parameters and powder characteristics were investigated. Field emission scanning electron microscope, X-ray diffraction, laser particle size analyzer, powder rheometer, and UV/visible/infrared spectrophotometer were used for analyses and measurements of micrographs, phases, granulometric parameters, flowability, and laser absorption properties of the powders, respectively. The results show that the obtained spherical powders exhibit good sphericity, smooth surfaces, favorable dispersity, and excellent fluidity under appropriate feeding rate and flow rate of carrier gas. Further, acicular microstructures of the spherical AlSi10Mg powders are composed of α-Al, Si, and a small amount of Mg2Si phase. In addition, laser absorption values of the spherical AlSi10Mg powders increase obviously compared with raw material, and different spectra have obvious absorption peaks at a wavelength of about 826 nm.

  18. Reactive wetting of amorphous silica by molten Al-Mg alloys and their interfacial structures

    NASA Astrophysics Data System (ADS)

    Shi, Laixin; Shen, Ping; Zhang, Dan; Jiang, Qichuan

    2016-07-01

    The reactive wetting of amorphous silica substrates by molten Al-Mg alloys over a wide composition range was studied using a dispensed sessile drop method in a flowing Ar atmosphere. The effects of the nominal Mg concentration and temperature on the wetting and interfacial microstructures were discussed. The initial contact angle for pure Al on the SiO2 surface was 115° while that for pure Mg was 35° at 1073 K. For the Al-Mg alloy drop, it decreased with increasing nominal Mg concentration. The reaction zone was characterized by layered structures, whose formation was primarily controlled by the variation in the alloy concentration due to the evaporation of Mg and the interfacial reaction from the viewpoint of thermodynamics as well as by the penetration or diffusion of Mg, Al and Si from the viewpoint of kinetics. In addition, the effects of the reaction and the evaporation of Mg on the movement of the triple line were examined. The spreading of the Al-Mg alloy on the SiO2 surface was mainly attributed to the formation of Mg2Si at the interface and the recession of the triple line to the diminishing Mg concentration in the alloy.

  19. Geometric and Chemical Composition Effects on Healing Kinetics of Voids in Mg-bearing Al Alloys

    NASA Astrophysics Data System (ADS)

    Song, Miao; Du, Kui; Wang, Chunyang; Wen, Shengping; Huang, Hui; Nie, Zuoren; Ye, Hengqiang

    2016-05-01

    The healing kinetics of nanometer-scale voids in Al-Mg-Er and Al-Mg-Zn-Er alloy systems were investigated with a combination of in situ transmission electron microscopy and electron tomography at different temperatures. Mg was observed completely healing the voids, which were then rejuvenated to the alloy composition with further aging, in the Al-Mg-Er alloy. On the contrary, Mg51Zn20 intermetallic compound was formed in voids in the Al-Mg-Zn-Er alloy, which leads to complete filling of the voids but not rejuvenation for the material. For voids with different geometrical aspects, different evolution processes were observed, which are related to the competition between bulk and surface diffusion of the alloys. For voids with a large size difference in their two ends, a viscous flow of surface atoms can be directly observed with in situ electron microscopy, when the size of one end becomes less than tens of nanometers.

  20. Elevated Temperature Deformation of Fe-39.8Al and Fe-15.6Mn-39.4Al

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel

    2004-01-01

    The elevated temperature compressive properties of binary Fe-39.8 at % Al and Fe-15.6Mn-39.4Al have been measured between 1000 and 1300 K at strain rates between 10(exp 7) and 10(exp 3)/ s. Although the Mn addition to iron aluminide did not change the basic deformation characteristics, the Mn-modified alloy was slightly weaker. In the regime where deformation of FeAl occurs by a high stress exponent mechanism (n = 6), strength increases as the grain size decreases at least for diameters between approx. 200 and approx. 10 microns. Due to the limitation in the grain size-flow stress-temperature-strain rate database, the influence of further reductions of the grain size on strength is uncertain. Based on the appearance of subgrains in deformed iron aluminide, the comparison of grain diameters to expected subgrain sizes, and the grain size exponent and stress exponent calculated from deformation experiments, it is believed that grain size strengthening is the result of an artificial limitation on subgrain size as proposed by Sherby, Klundt and Miller.

  1. RFe{sub 2}Mg{sub x}Al{sub 8−x} (R=La–Nd and Sm; x≈0.8): Flux synthesis, structure, magnetic and electrical properties

    SciTech Connect

    Ma, Xiaowei; Chai, Ping; Chen, Banghao; Lochner, Eric; Latturner, Susan E.

    2015-09-15

    Single crystals of Mg-substituted CeFe{sub 2}Al{sub 8} type intermetallics RFe{sub 2}Mg{sub x}Al{sub 8–x} (R=La–Nd and Sm; x≤1) were grown by reacting iron and rare earth metals in 1:1 Mg/Al mixed flux. The structure features mono-capped and bi-capped trigonal prismatic FeAl{sub 6} units. Electronic structure calculations indicate that magnesium substitution reduces the valence electron count, shifting the Fermi level away from a pseudo-gap. This changes the electronic nature of the cerium analog; the previously reported ternary CeFe{sub 2}Al{sub 8} shows strong hybridization between the cerium states and the conduction electrons, resulting in no magnetic moment on Ce atoms. On the other hand, magnetic susceptibility measurements on CeFe{sub 2}Mg{sub x}Al{sub 8–x} indicates a localized moment on cerium. The newly synthesized Pr, Nd and Sm analogs exhibit antiferromagnetic ordering at 2.8 K, 7.8 K and 12 K respectively. Solid state {sup 27}Al NMR of LaFe{sub 2}Mg{sub x}Al{sub 8–x} exhibits a broad Knight shift at ~1200 ppm, consistent with the metallic behavior shown by electrical resistivity data. - Graphical abstract: Mg substitution into CeFe{sub 2}Al{sub 8} modifies cerium valence due to changing valence electron count. - Highlights: • RFe{sub 2}Mg{sub x}Al{sub 8−x} (R=La–Nd, Sm) grow as large crystals from reactions in Mg/Al flux. • Products are magnesium-substituted variants of CeFe{sub 2}Al{sub 8}, with CaCo{sub 2}Al{sub 8} structure. • Ce magnetic moment in CeFe{sub 2}Mg{sub x}Al{sub 8−x} varies from that in CeFe{sub 2}Al{sub 8} due to VEC change. • Antiferromagnetic ordering observed for Pr, Nd, Sm analogs of RFe{sub 2}Mg{sub x}Al{sub 8−x}.

  2. Al-Ca and Al-Fe metal-metal composite strength, conductivity, and microstructure relationships

    SciTech Connect

    Kim, Hyong June

    2011-01-01

    Deformation processed metal-metal composites (DMMC’s) are composites formed by mechanical working (i.e., rolling, swaging, or wire drawing) of two-phase, ductile metal mixtures. Since both the matrix and reinforcing phase are ductile metals, the composites can be heavily deformed to reduce the thickness and spacing of the two phases. Recent studies have shown that heavily drawn DMMCs can achieve anomalously high strength and outstanding combinations of strength and conductivity. In this study, Al-Fe wire composite with 0.07, 0.1, and 0.2 volume fractions of Fe filaments and Al-Ca wire composite with 0.03, 0.06, and 0.09 volume fractions of Ca filaments were produced in situ, and their mechanical properties were measured as a function of deformation true strain. The Al-Fe composites displayed limited deformation of the Fe phase even at high true strains, resulting in little strengthening effect in those composites. Al-9vol%Ca wire was deformed to a deformation true strain of 13.76. The resulting Ca second-phase filaments were deformed to thicknesses on the order of one micrometer. The ultimate tensile strength increased exponentially with increasing deformation true strain, reaching a value of 197 MPa at a true strain of 13.76. This value is 2.5 times higher than the value predicted by the rule of mixtures. A quantitative relationship between UTS and deformation true strain was determined. X-ray diffraction data on transformation of Al + Ca microstructures to Al + various Al-Ca intermetallic compounds were obtained at the Advanced Photon Source at Argonne National Laboratory. Electrical conductivity was measured over a range of true strains and post-deformation heat treatment schedules.

  3. Chemical stability and Ce doping of LiMgAlF6 neutron scintillator

    SciTech Connect

    Du, M. H.

    2014-11-13

    We perform density functional calculations to investigate LiMgAlF6 as a potential neutron scintillator material. The calculations of enthalpy of formation and phase diagram show that single-phase LiMgAlF6 can be grown but it should be more difficult than growing LiCaAlF6 and LiSrAlF6. Moreover, the formation energy calculations for substitutional Ce show that the concentration of Ce on the Al site is negligible but a high concentration (>1 at.%) of Ce on the Mg site is attainable provided that the Fermi level is more than 5 eV lower than the conduction band minimum. Acceptor doping should promote Ce incorporation in LiMgAlF6.

  4. Chemical stability and Ce doping of LiMgAlF6 neutron scintillator

    DOE PAGES

    Du, M. H.

    2014-11-13

    We perform density functional calculations to investigate LiMgAlF6 as a potential neutron scintillator material. The calculations of enthalpy of formation and phase diagram show that single-phase LiMgAlF6 can be grown but it should be more difficult than growing LiCaAlF6 and LiSrAlF6. Moreover, the formation energy calculations for substitutional Ce show that the concentration of Ce on the Al site is negligible but a high concentration (>1 at.%) of Ce on the Mg site is attainable provided that the Fermi level is more than 5 eV lower than the conduction band minimum. Acceptor doping should promote Ce incorporation in LiMgAlF6.

  5. Plasma electrolytic oxidation coating of synthetic Al-Mg binary alloys

    SciTech Connect

    Tarakci, Mehmet

    2011-12-15

    The binary Al-Mg synthetic alloys were prepared in a vacuum/atmosphere controlled furnace with the addition of 0.5, 1, 2, 4, 7, and 15 wt.% pure Mg into pure aluminum as substrate material. The surfaces of the Al-Mg alloys and pure aluminum were coated for 120 min by plasma electrolytic oxidation in the same electrolyte of 12 g/L sodium silicate and 2 g/L KOH in distilled water. The coating was characterized by X-ray diffraction, scanning electron microscopy, profilometry and Vickers microhardness measurements. There regions of loose outer layer, dense inner layer with precipitate like particles of {alpha}-Al{sub 2}O{sub 3} and a thin transition layer were identified for the coated samples. The coating thickness increases from 85 to 150 {mu}m with Mg contents in the alloys. The surface morphology becomes more porous and consequently surface roughness tends to increase with plasma electrolytic oxidation treatment and further with Mg content. The increase in magnesium content reduces the formation of {alpha}-Al{sub 2}O{sub 3} and crystalline mullite phases in the coating and decreases microhardness of coating. The Mg concentration is constant throughout the other loose and dense regions of coating though it gradually decreases in the thin inner region. - Research Highlights: Black-Right-Pointing-Pointer The average thickness of PEO coating of Al-Mg alloys increases with Mg content. Black-Right-Pointing-Pointer The addition of Mg reduces and prevents the formation of {alpha}-Al{sub 2}O{sub 3} and mullite. Black-Right-Pointing-Pointer The surface roughness increases with Mg content in the Al-Mg alloys. Black-Right-Pointing-Pointer The hardness values of the coating decreases with the Mg amount in the substrate. Black-Right-Pointing-Pointer The Mg concentration is constant throughout the main regions of coating.

  6. Hydrogen permeation characteristics of some Fe-Cr-Al alloys

    NASA Astrophysics Data System (ADS)

    Van Deventer, E. H.; Maroni, V. A.

    1983-01-01

    Hydrogen permeation data are reported for two Fe-Cr-Al alloys, Type-405 SS (Cr 14-A1 0.2) and a member of the Fecralloy family of alloys (Cr 16-A1 5). The hydrogen permeability of each alloy (in a partially oxidized condition) was measured over a period of several weeks at randomly selected temperatures (between 150 and 850°C) and upstream H 2 pressures (between 2 and 1.5 × 10 4 Pa). The permeabilities showed considerable scatter with both time and temperature and were 10 2 to 10 3 times lower than those of pure iron, even in strongly reducing environments. The exponent, n, for the relationship between upstream H 2 pressure, P, and permeability, φ, ( φ ~ Pn) was closer to 0.7 than to the expected 0.5, indicating a process limited by surface effects (e.g., surface oxide films) as opposed to bulk material effects. Comparison of these results with prior permeation measurements on other Fe-Cr-Al alloys, on Fe-Cr alloys, and on pure iron shows that the presence of a few weight percent aluminum offers the best prospects for achieving low tritium permeabilities with martensitic and ferritic steels used in fusion-reactor first wall and blanket applications.

  7. Mg/2+/-Fe/2+/ order-disorder in cummingtonite, /Mg, Fe/7Si8O22/OH/2 - A new geothermometer.

    NASA Technical Reports Server (NTRS)

    Ghose, S.; Weidner, J. R.

    1972-01-01

    Determination of the temperature dependence of the Mg(2+)-Fe(2+) distribution between the M4 site and the M1, M2 and M3 sites in magnesium-rich cummingtonites by Fe-57 Mossbauer resonance spectroscopy. For the basic reversible ion-exchange reaction involved, the Gibbs free energy is estimated to be 3.6 to 4.1 kcal/mole, assuming an ideal solution model at each set of sites. The crystallization temperatures of two cummingtonite-bearing metamorphosed ultrabasic rocks are estimated to be 265 and 290 deg C. The Mossbauer resonance spectra are found to be an effective basis for detecting changes in site occupancies as a function of temperature.

  8. On the infiltration behavior of Al, Al-Li, and Mg melts through SiC{sub p} bed

    SciTech Connect

    Murty, B.S.; Thakur, S.K.; Dhindaw, B.K.

    2000-01-01

    Aluminum, Al-Li(8090), and Mg matrix composites with uniform distributions of SiC{sub p} reinforcement have been prepared by the vacuum infiltration technique. The infiltration kinetics have been found to increase in the order of Al, Al-Li, and Mg. The Al-Li alloy and Mg as matrix materials have shown improved wettability with SiC{sub p} in comparison to Al, leading to enhanced infiltration kinetics and reduced reinforcement degradation in the former cases. The infiltration kinetics are insensitive to preheat temperature beyond a critical temperature, which is close to the melting point of the matrix. A marginal improvement in infiltration kinetics could be obtained with Cu and Ni coating on SiC. The Vickers hardness, measured on the SiC p articles, has been shown to be an index of the strength of the interface between the matrix and reinforcement in the composite.

  9. Dissolution of Precipitates During Solution Treatment of Al-Mg-Si-Cu Alloys

    NASA Astrophysics Data System (ADS)

    Zhang, Xukai; Guo, Mingxing; Zhang, Jishan; Zhuang, Linzhong

    2016-02-01

    A model combining classical diffusion-controlled dissolution equation for a single spherical particle and Johnson-Mehl-Avrami-like equation is used to deal with dissolution process for different kinds of precipitations (Si, Mg2Si, Q(Al1.9Mg4.1Si3.3Cu)) in Al-Mg-Si-Cu alloys. The results reveal that the dissolution time of precipitates increases with increasing their sizes and solute concentrations in the alloy matrix; for the same size and concentration, their dissolution times follow Si > Q(Al1.9Mg4.1Si3.3Cu) > Mg2Si. Two precipitates (Mg2Si and Al1.9Mg4.1Si3.3Cu) with a size of about 700 nm were obtained in a cold rolled Al-Mg-Si-Cu-Zn alloy, and the complete dissolution time is about 15 seconds, which is basically the same as the calculated time by the developed model. The theoretical prediction of dissolution time can be greatly used to design solution treatment and thermomechanical processing parameters of Al-Mg-Si-Cu alloys.

  10. Oxygen fugacities determined from iron oxidation state in natural (Mg,Fe)O ferropericlase: new insights into lower mantle diamond formation

    NASA Astrophysics Data System (ADS)

    Longo, Micaela; McCammon, Catherine; Bulanova, Galina; Kaminsky, Felix; Tappert, Ralf

    2010-05-01

    Mineral inclusions in diamonds reflect the chemical composition and mineral assemblages of the two principal rock types occurring in the deep lithosphere, peridotite and eclogite. However, in the past two decades, the discovery of rare diamonds containing inclusions such as former Mg,Si-perovskite and (Mg,Fe)O ferropericlase led to the possibility that diamonds can form also at greater depths. (Mg,Fe)O ferropericlase is the most commonly found inclusion in lower mantle diamonds (more than 50% of the occurrences). Since the Fe3+ concentration in (Mg,Fe)O is sensitive to oxygen fugacity also at high pressures (Frost et al., 2004), the determination of Fe3+/Σ Fe in such inclusions provides a direct method for investigating lower mantle redox conditions during diamond formation. In the present study we explore whether variations in mantle oxygen fugacity exist as a function of chemical, physical and geographic parameters, by studying (Mg,Fe)O inclusions in lower mantle diamonds from a wide range of localities. Eighteen (Mg,Fe)O ferropericlase inclusions from lower mantle diamonds selected worldwide were measured by the flank method using the calibration previously established for synthetic ferropericlase (Longo et al., in preparation). The Fe3+/Σ Fe measured in (Mg,Fe)O inclusions of the present work (Juina, Brazil, Machado River, Brazil and Orroroo, Australia) were compared to data already available for other inclusions of larger size previously measured by Mössbauer spectroscopy (McCammon et al. 1997, 2004). Oxygen fugacity was estimated for each specimen relative to two reference buffers such as the Fe-(Mg,Fe)O buffer (reducing conditions) and the Re-ReO2 buffer (oxidizing conditions). Our results show a dependence on geographical location, and in particular, inclusions from the African province (Kankan Guinea) seem to record more reducing mantle conditions than the inclusions measured from the other provinces, which cover a larger range of fO2 conditions. It is

  11. Simultaneous desorption behavior of M borohydrides and Mg2FeH6 reactive hydride composites (M = Mg, then Li, Na, K, Ca)

    NASA Astrophysics Data System (ADS)

    Chaudhary, Anna-Lisa; Li, Guanqiao; Matsuo, Motoaki; Orimo, Shin-ichi; Deledda, Stefano; Sørby, Magnus H.; Hauback, Bjørn C.; Pistidda, Claudio; Klassen, Thomas; Dornheim, Martin

    2015-08-01

    Combinations of complex metal borohydrides ball milled with the transition metal complex hydride, Mg2FeH6, are analysed and compared. Initially, the Reactive Hydride Composite (RHC) of Mg2+ cation mixtures of Mg2FeH6 and γ-Mg(BH4)2 is combined in a range of molar ratios and heated to a maximum of 450 °C. For the molar ratio of 6 Mg2FeH6 + Mg(BH4)2, simultaneous desorption of the two hydrides occurred, which resulted in a single event of hydrogen release. This single step desorption occurred at temperatures between those of Mg2FeH6 and γ-Mg(BH4)2. Keeping this anionic ratio constant, the desorption behavior of four other borohydrides, Li-, Na-, K-, and Ca-borohydrides was studied by using materials ball milled with Mg2FeH6 applying the same milling parameters. The mixtures containing Mg-, Li-, and Ca-borohydrides also released hydrogen in a single event. The Mass Spectrometry (MS) results show a double step reaction within a narrow temperature range for both the Na- and K-borohydride mixtures. This phenomenon, observed for the RHC systems at the same anionic ratio with all five light metal borohydride mixtures, can be described as simultaneous hydrogen desorption within a narrow temperature range centered around 300 °C.

  12. Complex transition metal hydrides incorporating ionic hydrogen: thermal decomposition pathway of Na2Mg2FeH8 and Na2Mg2RuH8.

    PubMed

    Humphries, Terry D; Matsuo, Motoaki; Li, Guanqiao; Orimo, Shin-Ichi

    2015-03-28

    Complex transition metal hydrides have potential technological application as hydrogen storage materials, smart windows and sensors. Recent exploration of these materials has revealed that the incorporation of anionic hydrogen into these systems expands the potential number of viable complexes, while varying the countercation allows for optimisation of their thermodynamic stability. In this study, the optimised synthesis of Na2Mg2TH8 (T = Fe, Ru) has been achieved and their thermal decomposition properties studied by ex situ Powder X-ray Diffraction, Gas Chromatography and Pressure-Composition Isotherm measurements. The temperature and pathway of decomposition of these isostructural compounds differs considerably, with Na2Mg2FeH8 proceeding via NaMgH3 in a three-step process, while Na2Mg2RuH8 decomposes via Mg2RuH4 in a two-step process. The first desorption maxima of Na2Mg2FeH8 occurs at ca. 400 °C, while Na2Mg2RuH8 has its first maxima at 420 °C. The enthalpy and entropy of desorption for Na2Mg2TH8 (T = Fe, Ru) has been established by PCI measurements, with the ΔHdes for Na2Mg2FeH8 being 94.5 kJ mol(-1) H2 and 125 kJ mol(-1) H2 for Na2Mg2RuH8. PMID:25732233

  13. First stage of reaction of molten Al with MgO substrate

    SciTech Connect

    Morgiel, J.; Sobczak, N.; Pomorska, M.; Nowak, R.

    2015-05-15

    The Al/MgO couple was produced in vacuum (~ 5 × 10{sup −} {sup 4} Pa) by contact heating from RT up to 1000 °C and holding at that temperature for 1 h of a small 4 × 4 × 4 mm aluminium (5 N) sample placed on the [100] MgO single crystal substrate. TEM observations backed with electron diffraction analysis indicated that the interaction between liquid aluminium and MgO starts from a redox reaction producing a continuous layer of MgAl{sub 2}O{sub 4} spinel on the substrate surface. Its growth is controlled by solid state out-diffusion of magnesium and oxygen towards the surface being in contact with liquid metal. The thickening of spinel layer is accompanied by its cracking and infiltration with aluminium. The above process enables local dissolution of the MgO substrate and formation in it of a thin region of interpenetrating metallic channels walled with spinel. The removal of dissolved magnesium through open aluminium channels towards the drop and to vacuum locally produces areas of aluminium enriched with dissolved oxygen, which results in the nucleation of α-Al{sub 2}O{sub 3} at spinel clad walls. The growth of α-Al{sub 2}O{sub 3} is controlled only by the dissolution rate of MgO by aluminium, liquid state diffusion of Mg to drop/vacuum and oxygen to the front of the of α-Al{sub 2}O{sub 3} crystallites growing into MgO substrate. - Highlights: • New unique evidence of first stages of interaction of liquid Al with MgO substrates • Interaction of liquid Al with MgO starts with the formation of a layer MgAl{sub 2}O{sub 4}. • Growth of MgAl{sub 2}O{sub 4} is slow as controlled by solid state out-diffusion of Mg and O. • MgAl{sub 2}O{sub 4} serves as a nucleation site for Al{sub 2}O{sub 3} and consumed by it soon after. • Growth of Al{sub 2}O{sub 3} is fast as controlled by diffusion in liquid state.

  14. Fabrication and Analysis of the Wear Properties of Hot-Pressed Al-Si/SiCp + Al-Si-Cu-Mg Metal Matrix Composite

    NASA Astrophysics Data System (ADS)

    Bang, Jeongil; Oak, Jeong-Jung; Park, Yong Ho

    2016-01-01

    The aim of this study was to characterize microstructures and mechanical properties of aluminum metal matrix composites (MMC's) prepared by powder metallurgy method. Consolidation of mixed powder with gas atomized Al-Si/SiCp powder and Al-14Si-2.5Cu-0.5Mg powder by hot pressing was classified according to sintering temperature and sintering time. Sintering condition was optimized using tensile properties of sintered specimens. Ultimate tensile strength of the optimized sintered specimen was 228 MPa with an elongation of 5.3% in longitudinal direction. In addition, wear properties and behaviors of the sintered aluminum-based MMC's were analyzed in accordance with vertical load and linear speed. As the linear speed and vertical load of the wear increased, change of the wear behavior occurred in order of oxidation of Al-Si matrix, formation of C-rich layer, Fe-alloying to matrix, and melting of the specimen

  15. Al-Mg Isotope Study of Allende 5241

    NASA Technical Reports Server (NTRS)

    Kerekgyarto, A. G.; Jeffcoat, C. R.; Lapen, T. J.; Andreasen, R.; Righter, M.; Ross, D. K.; Simon, J. I.

    2016-01-01

    The defining characteristic of type B1 CAIs is a large (.5- 3mm) concentric melilite mantle [1]. In [2] we presented two isochrons from separate traverses across the melilite mantle of Allende EK 459-5-1. The primary petrographic differences between the traverses was the preservation of strong oscillatory zoning. The traverse that crossed the distinctive oscillatory zone produced a pristine internal isochron, while the other that did not have a strongly preserved oscillatory zone produced a disturbed isochron indicated by more scatter (higher MSWD) and a positive (delta)26Mg* intercept. The implication simply being that the oscillatory zone may represent varying conditions during the mantle formation event. We targeted a similar texture in Allende 5241 using the same methodology in an attempt to achieve similar results.

  16. Field Dependence of the Magnetic Roughness of CoFe(B)/MgO.

    NASA Astrophysics Data System (ADS)

    Idzerda, Yves; Dvorak, Joe; Negusse, Ezana; Lussier, Alex; Shinde, S. R.; Nagamine, Y.; Furukawa, S.; Tsunekawa, K.; Djayaprawira, D. D.

    2008-03-01

    We have measured the field dependent roughness of the magnetic interface of CoFe and CoFeB films covered by MgO by using diffuse X-ray resonant magnetic scattering (diffuse-XRMS) of circular polarized light. The samples studied were 3.0 nm of either a Co(70)Fe(30) or a Co(60)Fe(20)B(20) film covered by 1.8 nm MgO created by UHV sputtering system (ANELVA C-7100). By comparing the specular scattering map and the diffuse scattering map for a large range of incidence angles for photons resonantly tuned near the Co L3-edge as the applied magnetic field is swept through the coercive field, we have determined the chemical and magnetic roughness as a function of applied field. For the CoFe films, the magnetic scattering of the X-rays increases significantly as the film passes through the coercive field where the magnetic in-plane correlations are relatively short range, indicating the presence of small magnetic domains during moment reversal. For the CoFeB films, there is no significant increase in magnetic scattering at the coercive field, consistent with large domain switching.

  17. FeO and MgO in plagioclase of lunar anorthosites: Igneous or metamorphic?

    NASA Technical Reports Server (NTRS)

    Phinney, W. C.

    1994-01-01

    The combined evidence from terrestrial anorthosites and experimental laboratory studies strongly implies that lunar anorthosites have been subjected to high-grade metamorphic events that have erased the igneous signatures of FeO and MgO in their plagioclases. Arguments to the contrary have, to this point, been more hopeful than rigorous.

  18. Magnetic phase transitions in Ta/CoFeB/MgO multilayers

    SciTech Connect

    Barsukov, I.; Safranski, C.; Chen, Y.-J.; Youngblood, B.; Krivorotov, I. N.; Fu, Yu; Spasova, M.; Farle, M.; Katine, J. A.; Kuo, C. C.

    2015-05-11

    We study thin films and magnetic tunnel junction nanopillars based on Ta/Co{sub 20}Fe{sub 60}B{sub 20}/MgO multilayers by electrical transport and magnetometry measurements. These measurements suggest that an ultrathin magnetic oxide layer forms at the Co{sub 20}Fe{sub 60}B{sub 20}/MgO interface. At approximately 160 K, the oxide undergoes a phase transition from an insulating antiferromagnet at low temperatures to a conductive weak ferromagnet at high temperatures. This interfacial magnetic oxide is expected to have significant impact on the magnetic properties of CoFeB-based multilayers used in spin torque memories.

  19. Comparison of Tunneling in Fe-based Superconductors with Multi-band MgB2

    NASA Astrophysics Data System (ADS)

    Zasadzinski, John; Iavarone, Maria

    MgB2 is an s-wave, phonon coupled, multiband superconductor that exhibits novel tunneling spectra including a subtle dip feature due to quasiparticle transfer between bands. Since this feature mimics the above-gap spectral dip feature observed in Fe-based superconductors, typically attributed to a strong coupling boson, it is worthwhile to consider whether quasiparticle transfer is relevant. We first show that the dip in MgB2 appears in the π-band, DOS (Δ = 2.4 meV) and is due to quasiparticle transfer to the σ-band with Δ = 7.2 meV. Reviewing the spectral dip in Fe-based superconductors, including new data on FeSe crystals, there are inconsistencies with quasiparticle transfer as the origin. The conclusion is that the spectral dip is more likely due to a boson, the resonance spin excitation, as found in cuprate superconductors.

  20. Isotopic Fractionation of Mg2+(aq), Ca2+(aq), and Fe2+(aq) with Carbonate Minerals

    SciTech Connect

    Rustad, James R.; Casey, William H.; Yin, Qing-Zhu; Bylaska, Eric J.; Felmy, Andrew R.; Bogatko, Stuart A.; Jackson, Virgil E.; Dixon, David A.

    2010-11-15

    Density functional electronic structure calculations are used to compute the equilibrium constant (the isotope fractionation factor) for 26Mg/24Mg and 44Ca/40Ca isotope exchange between carbonate minerals and uncomplexed divalent aquo ions. The most reliable calculations at the B3LYP/6-311++G(2d,2p) level predict equilibrium constants K, reported as 103ln(K) at 25 °C, of -5.3, -1.1, and +1.1 for 26Mg/24Mg exchange between calcite (CaCO3), magnesite (MgCO3), and dolomite (Ca0.5Mg0.5CO3), respectively, and Mg2+(aq), with positive values indicating enrichment in the mineral phase. For 44Ca/40Ca exchange between calcite and Ca2+(aq), the calculations predict values of +1.5 for Ca2+(aq) in six-fold coordination and +4.1 for Ca2+(aq) in seven-fold coordination. We find that the reduced partition function ratios can be reliably computed from systems as small as M(CO3)610- and M2+(H2O)6 embedded in a set of fixed atoms representing the 2nd shell (and greater) coordination environment. We find that the aqueous cluster representing the aquo ion is much more sensitive to improvements in the basis set than the calculations on the mineral systems, and that fractionation factors should be computed using 2 the best possible basis set for the aquo complex, even if the reduced partition function ratio calculated with the same basis set is not available for the mineral system. The new calculations show that the previous discrepancies between theory and experiment for Fe3+-hematite and Fe2+-siderite fractionations arise from an insufficiently accurate reduced partition function ratio for the Fe3+(aq) and Fe2+(aq) species.

  1. Synchrotron in-situ deformation experiments of perovskite + (Mg,Fe)O aggregates under shallow lower mantle conditions (Invited)

    NASA Astrophysics Data System (ADS)

    Girard, J.; Amulele, G.; Farla, R. J.; Liu, Z.; Mohiuddin, A.; Karato, S.

    2013-12-01

    Experimental studies on rheological properties of mantle's minerals are crucial to understand the dynamics of Earth's interior, but direct experimental studies under the relevant lower mantle conditions are challenging. Most of the earlier studies were performed at lower mantle pressures but low temperatures using DAC (diamond anvil cell) (e.g., Merkel et al., 2003)), and in DAC experiments strain-rate and stress are unknown. Some previous studies were carried out under high pressures and high temperatures (e.g, Cordier et al., 2004) , but quantitative results on rheological behaviour of said minerals were not obtained. Here we present the results of the first in-situ deformation experiments of perovskite + (Mg,Fe)O (Pv + fp) aggregates using RDA (rotational Drickamer apparatus). The RDA has a better support for the anvils at high pressure than the more commonly used D-DIA apparatus and hence we can reach higher pressures and temperatures than the D-DIA. We have recently made new modifications to the cell assembly to reach the lower mantle conditions with less interference in X-ray diffraction patterns by the surrounding materials. The starting material was ringwoodite synthesized using a multi-anvil. In-situ deformation experiments were then carried at pressure up to 28 GPa (calculated from thermal EOS of Pt) and estimated temperatures up to 2200 K using RDA. Under these conditions, ringwoodite transformed to Pv + fp. We subsequently deformed the sample between strain rates of 10-4 to 10-5 s-1. Stress and strain were measured in-situ using X-ray synchrotron beam. The recovered sample analyses show evidence of perovskite+(Mg,Fe)O microstructure (Fig. 1). The radial X-ray diffraction data are being analysed to determine the stress levels of two minerals. Also microstructures of deformed specimens are studied to understand the deformation mechanisms and strain partitioning. The results will contribute towards our understanding of the rheological properties of the

  2. Chemical mixing at “Al on Fe” and “Fe on Al” interfaces

    SciTech Connect

    Süle, P.; Horváth, Z. E.; Kaptás, D.; Bujdosó, L.; Balogh, J.; Nakanishi, A.

    2015-10-07

    The chemical mixing at the “Al on Fe” and “Fe on Al” interfaces was studied by molecular dynamics simulations of the layer growth and by {sup 57}Fe Mössbauer spectroscopy. The concentration distribution along the layer growth direction was calculated for different crystallographic orientations, and atomically sharp “Al on Fe” interfaces were found when Al grows over (001) and (110) oriented Fe layers. The Al/Fe(111) interface is also narrow as compared to the intermixing found at the “Fe on Al” interfaces for any orientation. Conversion electron Mössbauer measurements of trilayers—Al/{sup 57}Fe/Al and Al/{sup 57}Fe/Ag grown simultaneously over Si(111) substrate by vacuum evaporation—support the results of the molecular dynamics calculations.

  3. Experimental Determination of Mechanisms and Rates of Fe-Mg Exchange Between Spinel Grains Mediated by a Fluid Phase

    NASA Astrophysics Data System (ADS)

    Mueller, T.; Dohmen, R.; Chakraborty, S.

    2008-12-01

    The overall mechanism and kinetics of mineral reactions results from a complex interaction of several processes such as surface reaction kinetics, volume diffusion and net transfer. In order to quantify the kinetics of reactions involving multiple phases in multicomponent systems, it is necessary to understand and characterize the nature and rates of each of these processes. Most laboratory experiments up to now have focused on kinetics of reactions where the reactants and products are in direct physical contact with each other. However, there is abundant textural evidence in rocks that reactions occurred between mineral grains that are physically separated from each other, frequently mediated by a fluid phase. We have devised an experimental setup to study the mechanism and kinetics of such reactions in the laboratory. Polished single crystals of two spinels (synthetic MgAl2O4 and a natural spinel with 44 mol% Hercynite component), 2mm on a side, were placed in a gold capsule (length: 2cm, diameter: 4mm) separated from each other by a 5mm long tube of Au or alumina. The capsule was welded shut after adding distilled water (80-100μl). Such capsules were annealed (2 Kbar, 700-750°C, up to 21 hours) in hydrothermal cold seal vessels. After annealing the crystals were cleaned in an ultrasonic bath in order to rinse them of possible quench products. The surfaces were examined optically and near surface chemistry was determined using Rutherford Backscattering Spectroscopy (RBS). We observe time dependent changes in the morphology as well as the chemistry of the crystals, as follows: After short times, the surface of the Mg spinel shows scattered etch pits while terraces form on the Fe spinel. After longer anneals, the etch pits disappear and the surface of the Mg spinels appear polished. Surface compositions are found to be different, depending on whether a Au or alumina separator was used in the experiments. The Fe rich spinel composition remains unchanged whereas

  4. Solid Solution Effects on the MgAl2O4 System

    SciTech Connect

    O'Hara, Kelley; Smith, Jeffrey D; Hemrick, James Gordon

    2009-01-01

    Phase relations between the binaries MgAl2O4-ZnAl2O4 and MgAl2O4-MgGa2O4 were studied. Stoichiometric MgAl2O4 spinel can be formed in the laboratory through a coprecipitation method. Complete solid solution formation in the MgAl2O4-MgGa2O4 system was confirmed through X-ray diffraction (XRD) analysis. XRD analysis of the MgAl2O4-ZnAl2O4 system did not confirm solid solution due to the similar lattice parameters of the two end points, however, previous studies have shown that complete solid solution does form. Thermal conductivity data is pending and will be included in the presentation. Based on previous experimentation and open literature, it is suspected that thermal conductivity will be decreased with the addition of solid solution. With increased amounts of disruption to the lattice from solid solution it is also theorized that the temperature at which the mean free path still impacts thermal conductivity could be increased.

  5. Effect of amorphous lamella on the crack propagation behavior of crystalline Mg/amorphous Mg-Al nanocomposites

    NASA Astrophysics Data System (ADS)

    Hai-Yang, Song; Yu-Long, Li

    2016-02-01

    The effects of amorphous lamella on the crack propagation behavior in crystalline/amorphous (C/A) Mg/Mg-Al nanocomposites under tensile loading are investigated using the molecular dynamics simulation method. The sample with an initial crack of orientation [0001] is considered here. For the nano-monocrystal Mg, the crack growth exhibits brittle cleavage. However, for the C/A Mg/Mg-Al nanocomposites, the ‘double hump’ behavior can be observed in all the stress-strain curves regardless of the amorphous lamella thickness. The results indicate that the amorphous lamella plays a critical role in the crack deformation, and it can effectively resist the crack propagation. The above mentioned crack deformation behaviors are also disclosed and analyzed in the present work. The results here provide a strategy for designing the high-performance hexagonal-close-packed metal and alloy materials. Project supported by the National Natural Science Foundation of China (Grant Nos. 11372256 and 11572259), the 111 Project (Grant No. B07050), the Program for New Century Excellent Talents in University of Ministry of Education of China (Grant No. NCET-12-1046), and the Program for New Scientific and Technological Star of Shaanxi Province, China (Grant No. 2012KJXX-39).

  6. Processes and time scales of magmatic evolution as revealed by Fe-Mg chemical and isotopic zoning in natural olivines

    NASA Astrophysics Data System (ADS)

    Oeser, Martin; Dohmen, Ralf; Horn, Ingo; Schuth, Stephan; Weyer, Stefan

    2015-04-01

    In this study, we applied high-precision in situ Fe and Mg isotope analyses by femtosecond laser ablation (fs-LA) MC-ICP-MS on chemically zoned olivine xeno- and phenocrysts from intra-plate volcanic regions in order to investigate the magnitude of Fe and Mg isotope fractionation and its suitability to gain information on magma evolution. Our results show that chemical zoning (i.e., Mg#) in magmatic olivines is commonly associated with significant zoning in δ56Fe and δ26Mg (up to 1.7‰ and 0.7‰, respectively). We explored different cases of kinetic fractionation of Fe and Mg isotopes by modeling diffusion in the melt or olivine and simultaneous growth or dissolution. Combining the information of chemical and isotopic zoning in olivine allows to distinguish between various processes that may occur during magma evolution, namely diffusive Fe-Mg exchange between olivine and melt, rapid crystal growth, and Fe-Mg inter-diffusion simultaneous to crystal dissolution or growth. Chemical diffusion in olivine appears to be the dominant process that drives isotope fractionation in magmatic olivine. Simplified modeling of Fe and Mg diffusion is suitable to reproduce both the chemical and the isotopic zoning in most of the investigated olivines and, additionally, provides time information about magmatic processes. For the Massif Central (France), modeling of diffusive re-equilibration of mantle olivines in basanites revealed a short time span (<2 years) between the entrainment of a mantle xenolith in an intra-plate basaltic magma and the eruption of the magma. Furthermore, we determined high cooling rates (on the order of a few tens to hundreds of °C per year) for basanite samples from a single large outcrop in the Massif Central, which probably reflects the cooling of a massive lava flow after eruption. Results from the modeling of Fe and Mg isotope fractionation in olivine point to a systematic difference between βFe and βMg (i.e., βFe/βMg ≈ 2), implying that the

  7. Interdiffusion and impurity diffusion in polycrystalline Mg solid solution with Al or Zn

    SciTech Connect

    Kammerer, Catherine; Kulkarni, Nagraj S; Warmack, Robert J Bruce; Sohn, Yong Ho

    2014-01-01

    Interdiffusion and impurity diffusion in Mg binary solid solutions, Mg(Al) and Mg(Zn) were investigated at temperatures ranging from 623 to 723 K. Interdiffusion coef cients were determined via the Boltzmann Matano Method using solid-to-solid diffusion couples assembled with polycrystalline Mg and Mg(Al) or Mg(Zn) solid solutions. In addition, the Hall method was employed to extrapolate the impurity diffusion coef cients of Al and Zn in pure polycrystalline Mg. For all diffusion couples, electron micro-probe analysis was utilized for the measurement of concentration pro les. The interdiffusion coef cient in Mg(Zn) was higher than that of Mg(Al) by an order of magnitude. Additionally, the interdiffusion coef cient increased signi cantly as a function of Al content in Mg(Al) solid solution, but very little with Zn content in Mg(Zn) solid solution. The activation energy and pre-exponential factor for the average effective interdiffusion coef cient in Mg(Al) solid solution were determined to be 186.8 ( 0.9) kJ/mol and 7.69 x 10-1 ( 1.80 x 10-1) m2/s, respectively, while those determined for Mg(Zn) solid solution were 139.5 ( 4.0) kJ/mol and 1.48 x 10-3 ( 1.13 x 10-3) m2/s. In Mg, the Zn impurity diffusion coef cient was an order of magnitude higher than the Al impurity diffusion coef cient. The activation energy and pre-exponential factor for diffusion of Al impurity in Mg were determined to be 139.3 ( 14.8) kJ/mol and 6.25 x 10-5 ( 5.37 x 10-4) m2/s, respectively, while those for diffusion of Zn impurity in Mg were determined to be 118.6 ( 6.3) kJ/mol and 2.90 x 10-5 ( 4.41 x 10-5) m2/s.

  8. Interfacial electronic structure-modulated magnetic anisotropy in Ta/CoFeB/MgO/Ta multilayers

    NASA Astrophysics Data System (ADS)

    Chen, Xi; Wang, Kai You; Wu, Zheng Long; Jiang, Shao Long; Yang, Guang; Liu, Yang; Teng, Jiao; Yu, Guang Hua

    2014-09-01

    We have observed several unexpected phenomena when a trace amount of Fe atoms is deposited onto the CoFeB/MgO interface in Ta/CoFeB/MgO/Ta multilayers. With the nominal thickness of the introduced Fe atoms (tFe) varying from 0 to 0.1 Å, the effective magnetic anisotropy energy (Keff) of annealed multilayers is remarkably enhanced from 1.28 × 106 erg/cm3 to 2.14 × 106 erg/cm3. As tFe further increasing, the Keff decreases and even becomes negative when tFe > 1 Å, indicating the change from perpendicular magnetic anisotropy to in-plane magnetic anisotropy. The analysis by X-ray photoelectron spectrometer reveals that the Fe atoms at annealed CoFeB/MgO interface show different electronic structures as tFe increasing, which combine with O atoms to form FeOx (x < 1), Fe2O3, and Fe3O4, respectively, leading to modulation of Fe 3d-O 2p orbital hybridization and thus the Keff. On the other hand, we find that the introduction of Fe atoms also helps to reduce the multilayers' magnetic damping.

  9. Interfacial electronic structure-modulated magnetic anisotropy in Ta/CoFeB/MgO/Ta multilayers

    SciTech Connect

    Chen, Xi; Jiang, Shao Long; Yang, Guang; Liu, Yang; Teng, Jiao; Yu, Guang Hua; Wang, Kai You; Wu, Zheng Long

    2014-09-01

    We have observed several unexpected phenomena when a trace amount of Fe atoms is deposited onto the CoFeB/MgO interface in Ta/CoFeB/MgO/Ta multilayers. With the nominal thickness of the introduced Fe atoms (t{sub Fe}) varying from 0 to 0.1 Å, the effective magnetic anisotropy energy (K{sub eff}) of annealed multilayers is remarkably enhanced from 1.28 × 10{sup 6 }erg/cm{sup 3} to 2.14 × 10{sup 6 }erg/cm{sup 3}. As t{sub Fe} further increasing, the K{sub eff} decreases and even becomes negative when t{sub Fe} > 1 Å, indicating the change from perpendicular magnetic anisotropy to in-plane magnetic anisotropy. The analysis by X-ray photoelectron spectrometer reveals that the Fe atoms at annealed CoFeB/MgO interface show different electronic structures as t{sub Fe} increasing, which combine with O atoms to form FeO{sub x} (x < 1), Fe{sub 2}O{sub 3}, and Fe{sub 3}O{sub 4}, respectively, leading to modulation of Fe 3d-O 2p orbital hybridization and thus the K{sub eff}. On the other hand, we find that the introduction of Fe atoms also helps to reduce the multilayers' magnetic damping.

  10. Magnetotransport Properties of Co2FeAl Nanowires

    NASA Astrophysics Data System (ADS)

    Sapkota, Keshab; Gyawali, P.; Dahal, Bishnu; Dulal, R.; Pegg, I. L.; Philip, John

    2013-03-01

    Co2FeAl (CFA) nanowire (NW) exhibit interesting magnetic behavior with temperature, which arises from the granular structure.[2] To understand the magnetotransport properties, single CFA NW devices were fabricated using standard electron beam lithography. The magnetoresistance measurements of single CFA NW device were carried out at different temperatures. The magnetoresistance measurements show oscillations as a function of applied external magnetic field. This work has been supported by funding from NSF under CAREER Grant No. ECCS-0845501 and NSF-MRI, DMR-0922997.

  11. Zener Relaxation Peak in an Fe-Cr-Al Alloy

    NASA Astrophysics Data System (ADS)

    Zhou, Zheng-Cun; Cheng, He-Fa; Gong, Chen-Li; Wei, Jian-Ning; Han, Fu-Sheng

    2002-11-01

    We have studied the temperature spectra of internal friction and relative dynamic modulus of the Fe-(25 wt%)Cr-(5 wt%)Al alloy with different grain sizes. It is found that a peak appears in the internal friction versus temperature plot at about 550°C. The peak is of a stable relaxation and is reversible, which occurs not only during heating but also during cooling. Its activation energy is 2.5 (+/- 0.15) eV in terms of the Arrhenius relation. In addition, the peak is not obvious in specimens with a smaller grain size. It is suggested that the peak originates from Zener relaxation.

  12. Dispersion strengthening of precipitation hardened Al-Cu-Mg alloys prepared by rapid solidification and mechanical alloying

    NASA Technical Reports Server (NTRS)

    Gilman, P. S.; Sankaran, K. K.

    1988-01-01

    Several Al-4Cu-1Mg-1.5Fe-0.75Ce alloys have been processed from either rapidly solidified or mechanically alloyed powder using various vacuum degassing parameters and consolidation techniques. Strengthening by the fine subgrains, grains, and the dispersoids individually or in combination is more effective when the alloys contain shearable precipitates; consequently, the strength of the alloys is higher in the naturally aged rather than the artificially aged condition. The strengths of the mechanically alloyed variants are greater than those produced from prealloyed powder. Properties and microstructural features of these dispersion strengthened alloys are discussed in regards to their processing histories.

  13. Tunneling behavior in ion-assist ion-beam sputtered CoFe/MgO/NiFe magnetic tunnel junctions

    SciTech Connect

    Singh, Braj Bhusan; Chaudhary, Sujeet; Pandya, Dinesh K.

    2012-11-15

    Graphical abstract: Display Omitted Highlights: ► Dual ion beam sputtered MgO barrier for MTJs. ► ∼12% TMR at 60 K. ► Glazman and Matveev model fitted for quantification of elastic and inelastic tunneling conductance through barrier. -- Abstract: Magnetic tunnel junctions (MTJs) consisting of CoFe and NiFe as ferromagnetic electrodes and MgO as insulating barrier fabricated through in situ shadow masking employing ion beam sputtering are studied for their tunneling magnetoresistance (TMR) and temperature dependence of the tunneling conductance behavior. The tunneling characteristics of these MTJs exhibited barrier height of 0.7 eV and width of 3.3 nm. These MTJs possessed ∼12% TMR at 60 K. The temperature dependence of conductance behavior of these junctions have revealed finite contributions from inelastic tunneling through the barrier via hopping conduction via present localized states which arise due to the presence of ionic interstitial defects in the MgO oxide barrier. The fitting of the data reveals that thirteenth order of hopping conduction is operative through MgO barrier.

  14. Half-metallicity in highly L21-ordered CoFeCrAl thin films

    NASA Astrophysics Data System (ADS)

    Jin, Y.; Kharel, P.; Valloppilly, S. R.; Li, X.-Z.; Kim, D. R.; Zhao, G. J.; Chen, T. Y.; Choudhary, R.; Kashyap, A.; Skomski, R.; Sellmyer, D. J.

    2016-10-01

    The structural, magnetic, and electron-transport properties of Heusler-ordered CoFeCrAl thin films are investigated experimentally and theoretically. The films, sputtered onto MgO and having thicknesses of about 100 nm, exhibit virtually perfect single-crystalline epitaxy and a high degree of L21 chemical order. X-ray diffraction and transmission-electron microscopy show that the structure of the films is essentially of the L21 Heusler type. The films are ferrimagnetic, with a Curie temperature of about 390 K, and a net moment of 2 μB per formula unit. The room temperature resistivity is 175 μΩ cm; the carrier concentration and mobility determined from the low temperature (5 K) measurement are 1.2 × 1018 cm-3 and 33 cm2/V s, respectively. In contrast to the well-investigated Heusler alloys such as Co2(Cr1-xFex)Al, the CoFeCrAl system exhibits two main types of weak residual A2 disorder, namely, Co-Cr disorder and Fe-Cr disorder, the latter conserving half-metallicity. Point-contact Andreev reflection yields a lower bound for the spin polarization, 68% at 1.85 K, but our structural and magnetization analyses suggest that the spin polarization at the Fermi level is probably higher than 90%. The high resistivity, spin polarization, and Curie temperature are encouraging in the context of spin electronics.

  15. Pressure-induced structural phase transition in AlN:Mg and AlN:Co nanowires

    SciTech Connect

    Xu, Yongsheng; Zhu, Hongyang; Ma, Chunli; Zhu, Pinwen; Cong, Ridong; Wu, Xiaoxin; Gao, Wei; Cui, Qiliang

    2013-06-15

    High-pressure behaviors of AlN:Mg and AlN:Co nanowires have been investigated by in situ angle dispersive synchrotron X-ray diffraction up to 41.5 GPa and 38.2 GPa, respectively. Their corresponding pressure-induced wurtzite-to-rocksalt phase transitions start at 17.7 GPa and 15.0 GPa and complete at 33.2 GPa and 31.0 GPa, respectively. The phase-transition routes are not affected by the doped ions, while the phase transition pressures are lower than that of pure AlN nanowires. The distinct high-pressure behaviors are ascribed to the doped ions, which reduce the formation energy of cation vacancies and induce Al vacancies defects together with substitution defects, resulting in lattice distortion and affecting structural stability and phase transition pressure. - Graphical abstract: The high-pressure behaviors of AlN:Mg and AlN:Co nanowires have been investigated by in situ angle dispersive synchrotron X-ray diffraction. - Highlights: • The high-pressure behaviors of AlN:Mg and AlN:Co nanowires have been investigated. • The pressure-induced wurtzite-to-rocksalt phase transitions have been observed. • The phase transition pressures are lower than that of pure AlN nanowires. • The distinct high-pressure behaviors are ascribed to the dopants. • The vacancy defects and substitution defects influence structural stability.

  16. Preparation of iron aluminate (FeAl2O4) nanoparticles from FeAl2O4 hollow particles fabricated by using a spray pyrolysis process

    NASA Astrophysics Data System (ADS)

    Yun, Jaecheol; Kim, Yangdo; Park, Dahee; Yun, Jung-Yeul

    2015-05-01

    Iron aluminate (FeAl2O4) hollow particles with a spinel structure were synthesized by using a spray pyrolysis process. FeAl2O4 hollow particles were formed at a reaction temperature of 900 °C at a flow rate of 40 L/min as a result of the rapid solvent evaporation and decomposition gases from the droplets in the spray solution prepared from metal salts and organic reagents. FeAl2O4 hollow particles were fabricated at a reaction temperature of 900 °C with a flow rate of 40 L/min. The FeAl2O4 hollow particles were heat treated for 3 hours at 600 °C in a 5% H2/Ar atmosphere to form the crystal particles. Subsequently, FeAl2O4 nanoparticles were fabricated from the FeAl2O4 hollow particles by using the wet milling process. After milling for 60 minutes, transmission electron microscopy revealed the FeAl2O4 particles to have a mean size of approximately 50 nm. The FeAl2O4 nanoparticles were fabricated successfully by using a two-step process, spray pyrolysis and wet milling.

  17. Cyclic Oxidation of FeCrAlY/Al2O3 Composites

    NASA Technical Reports Server (NTRS)

    Nesbitt, James A.; Draper, Susan L.; Barrett, Charles A.

    1999-01-01

    Three-ply FeCrAlY/Al2O3 composites and FeCrAlY matrix-only samples were cyclically oxidized at 1000 C and 1100 C for up to 1000 1-hr cycles. Fiber ends were exposed at the ends of the composite samples. Following cyclic oxidation, cracks running parallel to and perpendicular to the fibers were observed on the large surface of the composite. In addition, there was evidence of increased scale damage and spallation around the exposed fiber ends, particularly around the middle ply fibers. This damage was more pronounced at the higher temperature. The exposed fiber ends showed cracking between fibers in the outer plies, occasionally with Fe and Cr-rich oxides growing out of the cracks. Large gaps developed at the fiber/matrix interface around many of the fibers, especially those in the outer plies. Oxygen penetrated many of these gaps resulting in significant oxide formation at the fiber/matrix interface far within the composite sample. Around several fibers, the matrix was also internally oxidized showing Al2O3 precipitates in a radial band around the fibers. The results show that these composites have poor cyclic oxidation resistance due to the CTE mismatch and inadequate fiber/matrix bond strength at temperatures of 1000 C and above.

  18. Effect of Melt-to-Solid Insert Volume Ratio on Mg/Al Dissimilar Metals Bonding

    NASA Astrophysics Data System (ADS)

    Emami, S. M.; Divandari, M.; Arabi, H.; Hajjari, E.

    2013-01-01

    Compound casting is used as a process to join various similar and dissimilar metallic couples. The ratio of melt-to-solid volume is one of the main factors that can affect the contact time between melt and the solid insert. In this investigation, magnesium and aluminum metals (magnesium as the cast metal and aluminum as the solid insert) having melt-to-solid volume ratios ( V m/ V s) of 1.25, 3, and 5.25 were successfully bonded via compound casting. Results demonstrated that by increasing the ratio of V m/ V s from 1.25 to 5.25, the thickness of the reaction interface between Al and Mg varies within the range of 200 to 1800 μm. X-ray diffraction, scanning electron microscopy, and Vickers microhardness study of the bonding of these two metals showed that the interface consisted of three separate sub-layers within reaction layer. These sub-layers had higher hardness than those of the Al and Mg bulk metals. In all specimens, composition of the sub-layer adjacent to Al (layer I) was Al3Mg2 and that adjacent to Mg (layer III) was Al12Mg17/(Mg) eutectic structure. The intermediate layer composition (layer II) in specimens with volume ratio of 1.25 and 3 was a single-phase Al12Mg17, while for the case of volume ratio 5.25 this sub-layer consisted of Al12Mg17/(Mg) eutectic dispersed in Al12Mg17 intermetallic. The results of this research showed that in low melt/solid volume ratios, diffusion-reaction was the dominant mechanism for formation of Al-Mg intermetallic. However, when V m/ V s and the melt/solid insert contact time increased, the dominant mechanism of Al-Mg intermetallics changed to fusion-solidification due to increase in surface melting of the solid insert. Also the results of push-out tests showed that shear strengths of the interface decrease from 27.1 to 15.1 and 8.3 MPa for the Al/Mg couples prepared at 1.25, 3, and 5.25 V m/ V s respectively.

  19. Understanding the Origins of Intergranular Corrosion in Copper-Containing Al-Mg-Si Alloys

    NASA Astrophysics Data System (ADS)

    Kairy, Shravan K.; Alam, Talukder; Rometsch, Paul A.; Davies, Chris H. J.; Banerjee, Raj; Birbilis, Nick

    2016-03-01

    A definitive understanding of the mechanism of intergranular corrosion (IGC) in under-aged (UA) Cu-containing Al-Mg-Si alloys has not been clear to date. The grain boundary microstructure and chemistry in an UA Cu-containing Al-Mg-Si alloy were characterized by coupling atom probe tomography and scanning transmission electron microscopy. The rapid formation of an ultra-thin wetting Cu layer and discrete Q-phase (Al4Cu2Mg8Si7) precipitates along the grain boundaries, and a precipitate-free zone adjacent to the grain boundaries in the UA condition contribute to IGC.

  20. Forging of eccentric co-extruded Al-Mg compounds and analysis of the interface strength

    NASA Astrophysics Data System (ADS)

    Förster, W.; Binotsch, C.; Awiszus, B.; Lehmann, T.; Müller, J.; Kirbach, C.; Stockmann, M.; Ihlemann, J.

    2016-03-01

    Within the subproject B3 of the Collaborative Research Center 692 it has been shown that Al-Mg compounds with a good bonding quality can be produced by hydrostatic coextrusion. During processing by forging, the aluminum sleeve is thinned in areas of high strains depending on the component geometry. To solve this problem an eccentric core arrangement during co-extrusion was investigated. Based on the results of FE-simulations, the experimental validation is presented in this work. Rods with an offset of 0.25, 0.5 and 0.75 mm were produced by eccentric hydrostatic co-extrusion. Ultrasonic testing was used to evaluate the bonding quality across the entire rods. For the forging investigations the basic process Rising was chosen. The still good bonding quality after forging was examined by dye penetrant testing and optical microscopy. For an optimal stress transfer between the materials across the entire component, a sufficient bonding between the materials is essential. To evaluate the interface strength, a special bending test was developed. For the conception of the bending specimens it was required to analyze the Rising specimens geometry. These analyses were performed using a reconstruction of the geometrical data based on computer tomography (CT) investigations. The comparison with the numerically deter-mined Rising specimen geometry shows good correlation. Parametric Finite Element Analyses of the bending test were used to develop the load case and the specimen geometry. By means of iterative adaption of load application, bearing and specimen geometry parameters, an advantageous stress state and experimentally applicable configuration were found. Based on this conception, the experimental setup was configured and bending tests were performed. The interface strength was deter-mined by the calculation of the maximum interlaminar interfacial tension stress using the experimental interface failure force and the bending FE model.

  1. Phase Separation kinetics in an Fe-Cr-Al alloy

    SciTech Connect

    Capdevila, C.; Miller, Michael K; Chao, J.

    2012-01-01

    The {alpha}-{alpha}{prime} phase separation kinetics in a commercial Fe-20 wt.% Cr-6 wt.% Al oxide dispersion-strengthened PM 2000{trademark} steel have been characterized with the complementary techniques atom probe tomography and thermoelectric power measurements during isothermal aging at 673, 708, and 748 K for times up to 3600 h. A progressive decrease in the Al content of the Cr-rich {alpha}{prime} phase was observed at 708 and 748 K with increasing time, but no partitioning was observed at 673 K. The variation in the volume fraction of the {alpha}{prime} phase well inside the coarsening regime, along with the Avrami exponent 1.2 and activation energy 264 kJ mol{sup -1}, obtained after fitting the experimental results to an Austin-Rickett type equation, indicates that phase separation in PM 2000{trademark} is a transient coarsening process with overlapping nucleation, growth, and coarsening stages.

  2. Competitive Al3+ Inhibition of Net Mg2+ Uptake by Intact Lolium multiflorum Roots 1

    PubMed Central

    Rengel, Zdenko

    1990-01-01

    Rhizotoxicity of Al is more pronounced in younger plants. Effects of Al on nutrient uptake by plants of different age are poorly understood. The depletion technique was used to monitor net Mg2+ uptake from nutrient solutions by intact 15- and 35-day-old plants of two ryegrass (Lolium multiflorum Lam.) cultivars. Lowering the pH from 6.0 to 4.2 decreased the maximum net ion influx without affecting Km. Aluminum at 6.6 micromolar Al3+ activity increased Km indicating competitive inhibition. The effects of pH and 6.6 micromolar Al3+ on net Mg2+ uptake were much larger in 15- than in 35-day-old plants. Aluminum at 26 micromolar Al3+ activity competitively inhibited net Mg2+ uptake by 35-day-old plants, while causing time- and external Mg2+ activity-dependent net Mg2+ efflux from 15-day-old plants. The equilibrium constant (Ki) of a reversible combination of postulated plasmalemma Mg2+ transporter and Al3+ was calculated to be 2 and 5 micromolar Al3+ activity for 15-day-old plants of Wilo and Gulf ryegrass, respectively, and 21 micromolar Al3+ activity for 35-day-old plants of both cultivars. The Al3+-mediated increase in Km was larger for 15-day-old plants of the Al-sensitive cultivar `Wilo' than of the more Al-tolerant cultivar `Gulf,' while Al3+ affected 35-day-old plants of both cultivars to the same extent. PMID:16667588

  3. Local formation of a Heusler structure in CoFe-Al alloys

    NASA Astrophysics Data System (ADS)

    Wurmehl, S.; Jacobs, P. J.; Kohlhepp, J. T.; Swagten, H. J. M.; Koopmans, B.; Maat, S.; Carey, M. J.; Childress, J. R.

    2011-01-01

    We systematically study the changes in the local atomic environments of Co in CoFe-Al alloys as a function of Al content by means of nuclear magnetic resonance. We find that a Co2FeAl Heusler type structure is formed on a local scale. The observed formation of a highly spin-polarized Heusler compound may explain the improved magnetotransport properties in CoFe-Al based current-perpendicular-to-the-plane spin-valves.

  4. Investigation of structure in Al23 via resonant proton scattering of Mg22+p and the 22Mg(p,γ) Al23 astrophysical reaction rate

    NASA Astrophysics Data System (ADS)

    He, J. J.; Kubono, S.; Teranishi, T.; Notani, M.; Baba, H.; Nishimura, S.; Moon, J. Y.; Nishimura, M.; Iwasaki, H.; Yanagisawa, Y.; Hokoiwa, N.; Kibe, M.; Lee, J. H.; Kato, S.; Gono, Y.; Lee, C. S.

    2007-11-01

    Proton resonant states in Al23 have been investigated for the first time by the resonant elastic and inelastic scattering of Mg22+p with a Mg22 beam at 4.38 MeV/nucleon bombarding a thick (CH2)n target. The low-energy Mg22 beam was separated by the CNS radioactive ion beam separator (CRIB). The energy spectra of recoiled protons were measured at average scattering angles of θlab≈4°,17° and 23°. A new state has been observed at Ex=3.00 MeV with a spin-parity assignment of (3/2+). In addition, resonant inelastic scattering has populated three more states at excitation energies of 3.14, 3.26, and 3.95 MeV, with proton decay to the first excited state in Mg22 being observed. The new state at 3.95 MeV has been assigned a spin-parity of Jπ=(7/2+). The resonant parameters were determined by an R-matrix analysis of the excitation functions with a SAMMY-M6-BETA code. The core-excited structure of Al23 is discussed within a shell-model picture. The stellar reaction rate of the Mg22(p,γ)Al23 reaction has been reevaluated, and the revised total reaction rate is about 40% greater than the previous result for temperatures beyond T9=0.3.

  5. Interfacial reactions and wetting in Al-Mg sintered by powder metallurgy process

    NASA Astrophysics Data System (ADS)

    Faisal, Heny; Darminto, Triwikantoro, Zainuri, M.

    2016-04-01

    Was conducted to analyze the effect of temperature variation on the bonding interface sintered composite Al-Mg and analyze the effect of variations of the density and hardness sinter. Research carried out by the base material powders of Al, Mg powder and solvent n-butanol. The method used in this study is a powder metallurgy, with a composition of 60% volume fraction of Al - 40% Mg. Al-Mg mixing with n-butanol for 1 hour at 500 rpm. Then the emphasis (cold comression) with a size of 1.4 cm in diameter dies and height of 2.8 cm, is pressed with a force of 20 MPa and held for 15 minutes. After the sample into pellets, then sintered at various temperatures 300 °C, 350 °C, 400 °C and 450 °C. Characterization is done by using the testing green density, sintered density, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), vickers microhardness, and press test. XRD data analysis done by using X'Pert High Score Plus (HSP) to determine whether there is a new phase is formed. Test results show that the sintered density increasing sintering temperature, the resulting density is also increasing (shrinkage). However, at a temperature of 450 °C decreased (swelling). With the increased sinter density, interfacial bonding getting Kuta and more compact so that its hardness is also increased. From the test results of SEM / EDX, there Mg into Al in the border area. At temperatures of 300 °C, 350 °C, 400 °C, the phase formed is Al, Mg and MgO. While phase is formed at a temperature of 450 °C is aluminum magnesium (Al3Mg2), Aluminum Magnesium Zinc (AlMg2Zn).

  6. Importance of doping and frustration in itinerant Fe-doped Cr2Al

    DOE PAGES

    Susner, M. A.; Parker, D. S.; Sefat, A. S.

    2015-05-12

    We performed an experimental and theoretical study comparing the effects of Fe-doping of Cr2Al, an antiferromagnet with a N el temperature of 670 K, with known results on Fe-doping of antiferromagnetic bcc Cr. (Cr1-xFex)2Al materials are found to exhibit a rapid suppression of antiferromagnetic order with the presence of Fe, decreasing TN to 170 K for x=0.10. Antiferromagnetic behavior disappears entirely at x≈0.125 after which point increasing paramagnetic behavior is exhibited. Moreover, this is unlike the effects of Fe doping of bcc antiferromagnetic Cr, in which TN gradually decreases followed by the appearance of a ferromagnetic state. Theoretical calculations explainmore » that the Cr2Al-Fe suppression of magnetic order originates from two effects: the first is band narrowing caused by doping of additional electrons from Fe substitution that weakens itinerant magnetism; the second is magnetic frustration of the Cr itinerant moments in Fe-substituted Cr2Al. In pure-phase Cr2Al, the Cr moments have an antiparallel alignment; however, these are destroyed through Fe substitution and the preference of Fe for parallel alignment with Cr. This is unlike bulk Fe-doped Cr alloys in which the Fe anti-aligns with the Cr atoms, and speaks to the importance of the Al atoms in the magnetic structure of Cr2Al and Fe-doped Cr2Al.« less

  7. Formation of layered Fe(II)-Al(III)-hydroxides during reaction of Fe(II) with aluminum oxide.

    PubMed

    Elzinga, Evert J

    2012-05-01

    The reactivity of aqueous Fe(II) with aluminum oxide in anoxic solutions was investigated with batch kinetic experiments combined with Fe K edge X-ray absorption spectroscopy measurements to characterize Fe(II) sorption products. Formation of Fe(II)-Al(III)-layered double hydroxides with an octahedral sheet structure similar to nikischerite (NaFe(II)(6) Al(3)(SO(4))(2)(OH)(18) (H(2)O)(12)) was observed within a few hours during sorption at pH 7.5 and aqueous Fe(II) concentrations of 1-3 mM. These Fe(II) phases are composed of brucite-like Fe(II)(OH)(2) sheets with partial substitution of Al(III) for Fe(II), charge balanced by anions coordinated along the basal planes. Their fast rate of formation suggests that these previously unrecognized Fe(II) phases, which are structurally and compositionally similar to green rust, may be an important sink of Fe(II) in suboxic and anoxic geochemical environments, and impact the fate of structurally compatible trace metals, such as Co(II), Ni(II), and Zn(II), as well as redox-reactive species including Cr(VI) and U(VI). Further studies are required to assess the thermodynamics, formation kinetics, and stability of these Fe(II) minerals under field conditions. PMID:22409244

  8. Preparation of Co{sub 2}FeSn Heusler alloy films and magnetoresistance of Fe/MgO/Co{sub 2}FeSn magnetic tunnel junctions

    SciTech Connect

    Tanaka, M. A.; Ishikawa, Y.; Wada, Y.; Hori, S.; Murata, A.; Horii, S.; Yamanishi, Y.; Mibu, K.; Kondou, K.; Ono, T.; Kasai, S.

    2012-03-01

    To obtain magnetic tunnel junctions (MTJs) composed of non-equilibrium alloy, Co{sub 2}FeSn films were prepared by atomically controlled alternate deposition at various substrate temperatures. X-ray diffraction patterns and Moessbauer spectra clarify that Co{sub 2}FeSn films in the Heusler alloy phase can be realized by growing at a substrate temperature of 250 deg. C or below. Phase separation into cubic CoSn, hexagonal CoSn and cubic CoFe phases occurs in films grown at substrate temperatures 300 deg. C or greater. Fe/MgO/Co{sub 2}FeSn MTJs were prepared with the Co{sub 2}FeSn layer grown at various substrate temperatures. The MTJs with the ferromagnetic Co{sub 2}FeSn layer grown at a substrate temperature of 250 deg. C showed tunnel magnetoresistance ratios of 72.2% and 43.5% at 2 K and 300 K, respectively.

  9. Effect of scandium on the microstructure and ageing behaviour of cast Al-6Mg alloy

    SciTech Connect

    Kaiser, M.S.; Datta, S.; Roychowdhury, A. Banerjee, M.K.

    2008-11-15

    Microstructural modification and grain refinement due to addition of scandium in Al-6Mg alloy has been studied. Transmission electron microscopy is used to understand the microstructure and precipitation behaviour in Al-6Mg alloy doped with scandium. It is seen from the microstructure that the dendrites of the cast Al-6Mg alloy have been refined significantly due to addition of scandium. Increasing amount of scandium leads to a greater dendrite refinement. The age hardening effect in scandium added Al-6Mg alloys has been studied by subjecting the alloys containing varying amount of scandium ranging from 0.2 wt.% to 0.6 wt.% to isochronal and isothermal ageing at various temperatures for different times. It is observed that significant hardening takes place in the aged alloys due to the precipitation of scandium aluminides.

  10. Stress corrosion cracking and hydrogen embrittlement of an Al-Zn-Mg-Cu alloy

    SciTech Connect

    Song, R.G.; Dietzel, W.; Zhang, B.J.; Liu, W.J.; Tseng, M.K.; Atrens, A

    2004-09-20

    The age hardening, stress corrosion cracking (SCC) and hydrogen embrittlement (HE) of an Al-Zn-Mg-Cu 7175 alloy were investigated experimentally. There were two peak-aged states during ageing. For ageing at 413 K, the strength of the second peak-aged state was slightly higher than that of the first one, whereas the SCC susceptibility was lower, indicating that it is possible to heat treat 7175 to high strength and simultaneously to have high SCC resistance. The SCC susceptibility increased with increasing Mg segregation at the grain boundaries. Hydrogen embrittlement (HE) increased with increased hydrogen charging and decreased with increasing ageing time for the same hydrogen charging conditions. Computer simulations were carried out of (a) the Mg grain boundary segregation using the embedded atom method and (b) the effect of Mg and H segregation on the grain boundary strength using a quasi-chemical approach. The simulations showed that (a) Mg grain boundary segregation in Al-Zn-Mg-Cu alloys is spontaneous, (b) Mg segregation decreases the grain boundary strength, and (c) H embrittles the grain boundary more seriously than does Mg. Therefore, the SCC mechanism of Al-Zn-Mg-Cu alloys is attributed to the combination of HE and Mg segregation induced grain boundary embrittlement.

  11. Effects of Composition and Iron Spin State on the Structural Transition of (Mg,Fe)CO3 in the Earth's Lower Mantle

    NASA Astrophysics Data System (ADS)

    Hsu, H.; Huang, S. C.; Wei, C. M.; Hsing, C. R.

    2015-12-01

    Iron-bearing magnesium carbonates (Mg,Fe)CO3 are believed the major carbon carriers in the Earth's deep lower mantle; they may play a crucial role in the Earth's deep carbon cycle. Knowledge of the physical and chemical properties of these carbonates is thus essential for our understanding of the mantle's role in global carbon cycle. Experiments have shown that (Mg,Fe)CO3 ferromagnesite (calcite structure) can be stable up to 80-100 GPa. At 45-50 GPa, ferromangsite undergoes a high-spin to low-spin transition, accompanied by a volume reduction and elastic anomalies. Starting ~100 GPa, ferromagnesite goes through a complicated structural transition. The detail of this transition and the atomic structures of high-pressure (Mg,Fe)CO3 phases are still highly debated. Experimental observations and theoretical results are inconsistent so far. In experiments, several distinct high-pressure (Mg,Fe)CO3 structures have been reported, including a P21/c phase [1] and a Pmm2 phase [2]. In theory, a C2/m phase [3] and a P-1 phase [4] have been suggested, while the Pmm2 phase is not found. One possible reason for such a discrepancy is that all available theoretical calculations so far are based on pure MgCO3, while experimental works are performed using (Mg,Fe)CO3 with high iron concentration ( > 50%). Clearly, the concentration of iron and the possible iron spin crossover can significantly affect the stability of these high-pressure (Mg,Fe)CO3 phases. Here, we use density functional theory + self-consistent Hubbard U (DFT+Usc) calculations to study this structural transition. The effects of composition and iron spin state on these (Mg,Fe)CO3 phases are also discussed. Our results can be expected to provide insightful information for better understanding the Earth's deep carbon cycle.[1] E. Boulard et al., Proc. Natl. Acad. Sci. USA 108, 5184 (2011).[2] J. Liu et al., Sci. Rep. 5, 7640 (2015). [3] A. R. Oganov et al., Earth Planet. Sci. Lett. 273, 38 (2008). [4] C. J. Pickard and

  12. The roles of Zr and Mn in processing and superplasticity of Al-Mg alloys

    NASA Technical Reports Server (NTRS)

    Mcnelley, Terry R.; Hales, S. J.

    1990-01-01

    Processing studies have been conducted on two alloys, of nominal compositions Al-10Mg-0.1Zr or Al-10Mg-0.5Mn, in order to clarify the role of the dispersoid forming Zr or Mn additions. Mechanical property data reveal that the Mn-containing alloy has a lower maximum elongation but exhibits superplastic response over a broader range of temperature. Microstructural investigations and texture analyses were utilized to assess the effect of the presence of Al8Mg5 precipitates in combination with either Al3Zr or Al6Mn dispersoid particles during isothermal rolling at 300 C and subsequent tensile deformation at temperatures from 200-425 C.

  13. Nanostructured Mg-Al hydrotalcite as catalyst for fine chemical synthesis.

    PubMed

    Basahel, Sulaiman N; Al-Thabaiti, Shaeel A; Narasimharao, Katabathini; Ahmed, Nesreen S; Mokhtar, Mohamed

    2014-02-01

    This paper reviews the recent research of nanostructured Mg-Al hydrotalcite (Mg-Al HT) and its application as an efficient solid base catalyst for the synthesis of fine chemicals. Mg-Al HT has many beneficial features, such as low cost, selectivity, catalytic properties, and wide range of preparation and modification methods. They hold promise for providing sought-after, environmentally friendly technologies for the 21st century. Replacement of currently used homogeneous alkaline bases for the synthesis of fine chemicals by a solid catalyst can result in catalyst re-use and waste stream reduction. We introduce briefly the structure, properties and characterization of the nanostructured Mg-Al HT. The efficacy and benign applications of Mg-Al HT as an alternative solid base to homogenous catalysts in the synthesis of fine chemicals are then reviewed. The challenges for the future applications of Mg-Al HT in the synthesis of fine chemicals in terms of green protocol processes are discussed. PMID:24749466

  14. Cryogenic and elevated temperature strengths of an Al-Zn-Mg-Cu alloy modified with Sc and Zr

    NASA Astrophysics Data System (ADS)

    Senkova, S. V.; Senkov, O. N.; Miracle, D. B.

    2006-12-01

    The effect of minor additions of Sc and Zr on tensile properties of two developmental Al-Zn-Mg-Cu alloys was studied in the temperature range -196°C to 300°C. Due to the presence of Sc and Zr in a fine dispersoid form, both low-temperature and elevated temperature strengths of these alloys are much higher than those of similar 7000 series alloys that do not contain these elements. After short holding times (up to 10 hours) at 205°C, the strength of these alloys is higher than those of high-temperature Al alloys 2219-T6 and 2618-T6; however, the latter alloys show better strength after longer holding times. It is suggested that additional alloying of the Sc-containing Al-Zn-Mg-Cu alloys with other dispersoid-forming elements, such as Ni, Fe, Mn, and Si, with a respective decrease in the amounts of Zn and Mg may further improve the elevated temperature strength and decrease the loss of strength with extended elevated temperature exposure.

  15. Discharge properties of Mg-Al-Mn-Ca and Mg-Al-Mn alloys as anode materials for primary magnesium-air batteries

    NASA Astrophysics Data System (ADS)

    Yuasa, Motohiro; Huang, Xinsheng; Suzuki, Kazutaka; Mabuchi, Mamoru; Chino, Yasumasa

    2015-11-01

    The discharge behaviors of rolled Mg-6 mass%Al-0.3 mass%Mn-2 mass%Ca (AMX602) and Mg-6 mass%Al-0.3 mass%Mn (AM60) alloys used as anodes for Magnesium-air batteries were investigated. The AMX602 alloy exhibited superior discharge properties compared to the AM60 alloy, especially at low current density. The discharge products of the AMX602 alloy were dense and thin, and many cracks were observed at all current densities. In addition, the discharge products were detached at some sites. These sites often corresponded to the positions of Al2Ca particles. The comparison of the discharge and corrosion tests indicated that the dense and thin discharge products of AMX602 were easily cracked by dissolution of the Mg matrix around Al2Ca particles, and the cracks promoted the penetration of the electrolyte into the discharge products, retaining the discharge activity. In contrast, concerning the AM60 alloy, thick discharge products were formed on the surface during discharge, and cracking of the discharge products hardly occurred, degrading the discharge properties. Localized and deeply corroded pits that could result from the detachment of metal pieces from the anode during discharge were partly observed in the AM60 alloy. It is suggested that these detached metal pieces are another reason for the low discharge properties of the AM60 alloy.

  16. Flux jump behaviors and mechanism of FeTi doped MgB2 at 5 K

    NASA Astrophysics Data System (ADS)

    Lee, H. B.; Kim, G. C.; Kim, Y. C.; Ahmad, D.

    2015-08-01

    This study examined the flux jump behaviors of Fe-doped MgB2 according to content of FeTi particles at 5 K, at which flux jump has been shown to be more frequent. The samples were synthesized in a stainless steel tube with Mg, B and FeTi particles. The motives of flux jump in MgB2 superconductors are over-moving fluxes around the defects and the low heat capacity of MgB2. MgB2 was doped with FeTi particles to overcome these vulnerable points of MgB2. The flux jump of MgB2 decreased with increasing content of doped FeTi particles. On the other hand, excessive doping of FeTi resulted in a decrease of diamagnetic properties and the flux pinning effects together. It is concluded that FeTi particles in MgB2 do not block the flux jump itself, but the propagation of flux jump of MgB2.

  17. Effect of MgO/Fe Interface Oxidation State on Electric-Field Modulation of Interfacial Magnetic Anisotropy

    NASA Astrophysics Data System (ADS)

    Guan, X. W.; Cheng, X. M.; Wang, S.; Huang, T.; Xue, K. H.; Miao, X. S.

    2016-06-01

    The impact of the MgO/Fe interface oxidation state on the electric-field-modified magnetic anisotropy in MgO/Fe has been revealed by density functional calculations. It is shown that the influence of the interface oxidation is strong enough to dominate the effect of the electric field on the magnetic anisotropy of MgO/Fe-based films. The magnetoelectric coefficients are calculated to be positive for the ideal and overoxidized MgO/Fe interface, but an abnormal negative value emerges in the underoxidized case. By analyzing the interface states based on density of states and band structures, we demonstrate that the considerably different electronic structures of the three oxidized MgO/Fe interfaces lead to the strong discrepancy in the electric-field modulation of the interfacial magnetic anisotropy. These results are of considerable interest in the area of electric-field-controlled magnetic anisotropy and switching.

  18. Perpendicular magnetic anisotropy and magnetization dynamics in oxidized CoFeAl films

    NASA Astrophysics Data System (ADS)

    Wu, Di; Zhang, Zhe; Li, Le; Zhang, Zongzhi; Zhao, H. B.; Wang, J.; Ma, B.; Jin, Q. Y.

    2015-07-01

    Half-metallic Co-based full-Heusler alloys with perpendicular magnetic anisotropy (PMA), such as Co2FeAl in contact with MgO, are receiving increased attention recently due to its full spin polarization for high density memory applications. However, the PMA induced by MgO interface can only be realized for very thin magnetic layers (usually below 1.3 nm), which would have strong adverse effects on the material properties of spin polarization, Gilbert damping parameter, and magnetic stability. In order to solve this issue, we fabricated oxidized Co50Fe25Al25 (CFAO) films with proper thicknesses without employing the MgO layer. The samples show controllable PMA by tuning the oxygen pressure (PO2) and CFAO thickness (tCFAO), large perpendicular anisotropy field of ~8.0 kOe can be achieved at PO2 = 12% for the sample of tCFAO = 2.1 nm or at PO2 = 7% for tCFAO = 2.8 nm. The loss of PMA at thick tCFAO or high PO2 results mainly from the formation of large amount of CoFe oxides, which are superparamagnetic at room temperature but become hard magnetic at low temperatures. The magnetic CFAO films, with strong PMA in a relatively wide thickness range and small intrinsic damping parameter below 0.028, would find great applications in developing advanced spintronic devices.

  19. Perpendicular magnetic anisotropy and magnetization dynamics in oxidized CoFeAl films

    PubMed Central

    Wu, Di; Zhang, Zhe; Li, Le; Zhang, Zongzhi; Zhao, H. B.; Wang, J.; Ma, B.; Jin, Q. Y.

    2015-01-01

    Half-metallic Co-based full-Heusler alloys with perpendicular magnetic anisotropy (PMA), such as Co2FeAl in contact with MgO, are receiving increased attention recently due to its full spin polarization for high density memory applications. However, the PMA induced by MgO interface can only be realized for very thin magnetic layers (usually below 1.3 nm), which would have strong adverse effects on the material properties of spin polarization, Gilbert damping parameter, and magnetic stability. In order to solve this issue, we fabricated oxidized Co50Fe25Al25 (CFAO) films with proper thicknesses without employing the MgO layer. The samples show controllable PMA by tuning the oxygen pressure (PO2) and CFAO thickness (tCFAO), large perpendicular anisotropy field of ~8.0 kOe can be achieved at PO2 = 12% for the sample of tCFAO = 2.1 nm or at PO2 = 7% for tCFAO = 2.8 nm. The loss of PMA at thick tCFAO or high PO2 results mainly from the formation of large amount of CoFe oxides, which are superparamagnetic at room temperature but become hard magnetic at low temperatures. The magnetic CFAO films, with strong PMA in a relatively wide thickness range and small intrinsic damping parameter below 0.028, would find great applications in developing advanced spintronic devices. PMID:26190066

  20. Study on effects of powder and flake chemistry and morphology on the properties of Al-Cu-Mg-X-X-X powder metallurgy advanced aluminum alloys

    NASA Technical Reports Server (NTRS)

    Meschter, P. J.; Lederich, R. J.; Oneal, J. E.

    1986-01-01

    A study was conducted: (1) to develop rapid solidification processed (RSP) dispersoid-containing Al-3Cu-2Li-1Mg-0.2Zr alloys as substitutes for titanium alloys and commercial 2XXX aluminum alloys for service to at least 150 C; and (2) to develop RSP Al-4Li-Cu-Mg-Zr alloys as substitutes for high-strength commercial 7XXX alloys in ambient-temperature applications. RSP Al-3Cu-2Li-1Mg-0.2Zr alloys have density-normalized yield stresses at 150 C up to 52% larger than that of 2124-T851 and up to 30% larger than that of Ti-6Al-4V. Strength at 150 C in these alloys is provided by thermally stable delta' (Al3Li), T1 (Al2LiCu), and S' (Al2CuMg) precipitates. Density-normalized yield stresses of RSP Al-3Cu-2Li-1Mg-0.2Zr alloys are up to 100% larger than that of 2124-T851 and equivalent to that of Al-8Fe-4Ce at 260 C. Strength in the RSP alloys at 260 C is provided by incoherent dispersoids and subboundary constituent particles such as T1 and S. The RSP alloys are attractive substitutes in less than or = 100-h exposures for 2xxx and Al-4Fe-Ce alloys up to 260 C and for titanium alloys up to 150 C. RSP Al-4Li-Cu-Mg-Zr alloys have ambient-temperature yield and ultimate tensile stresses similar to that of 7050-T7651, and are 14% less dense. RSP Al-4Li-0.5Cu-1.5Mg-0.2Zr has a 20% higher specific yield stress, 40% higher specific elastic modulus, and superior corrosion resistance compared to the properties of 7050-T7651. Strength in the Al-4Li-Cu-Mg-Zr alloy class is primarily provided by the substructure and delta' precipitates and is independent of Cu:Mg ratio. Improvements in fracture toughness and transverse-orientation properties in both alloy classes depend on improved melt practices to eliminate oxide inclusions which are incorporated into the consolidated forms.

  1. Formation enthalpies of Al-Fe-Zr-Nd system calculated by using geometric and Miedema's models

    NASA Astrophysics Data System (ADS)

    Zhang, Lei; Wang, Rongcheng; Tao, Xiaoma; Guo, Hui; Chen, Hongmei; Ouyang, Yifang

    2015-04-01

    Formation enthalpy is important for the phase stability and amorphous forming ability of alloys. The formation enthalpies of Fe17RE2 (RE=Ce, Pr, Nd, Gd and Er) obtained by Miedema's theory are in good agreement with those of the experiments. The dependence of formation enthalpy on concentration of Al for intermetallic (AlxFe1-x)17Nd2 have been calculated by Miedema's theory and the geometric model. The solid solubility of Al in (AlxFe1-x)17Nd2 is coincident with the concentration dependence of formation enthalpy. The mixing enthalpies of liquid alloys and formation enthalpies of alloys for Al-Fe-Zr-Nd system have been predicted. The calculated mixing enthalpy indicates that the adding of Fe or Nd decreases monotonously the magnitude of enthalpy. The formation enthalpies of Al-Fe-Zr-Nd system indicate that the shape of the enthalpy contour map changes when the content of Al is less than 50.0 at% and then it remains unchanged except the decrease of magnitude. The formation enthalpy of Al-Fe-Zr-Nd increases with the increase of Fe and/or Nd content. The negative formation enthalpy indicates that Al-Fe-Zr-Nd system has higher amorphous forming ability and wide amorphous forming range. The certain contents of Zr and/or Al are beneficial for the formation of Al-Fe-Zr-Nd intermetallics.

  2. First-principles study of the Fe | MgO(0 0 1) interface: magnetic anisotropy.

    PubMed

    Bose, Thomas; Cuadrado, Ramon; Evans, Richard F L; Chepulskii, Roman V; Apalkov, Dmytro; Chantrell, Roy W

    2016-04-20

    We present a systematic first-principles study of Fe | MgO bilayer systems emphasizing the influence of the iron layer thickness on the geometry, the electronic structure and the magnetic properties. Our calculations ensure the unconstrained structural relaxation at scalar relativistic level for various numbers of iron layers placed on the magnesium oxide substrate. Our results show that due to the formation of the interface the electronic structure of the interface iron atoms is significantly modified involving charge transfer within the iron subsystem. In addition, we find that the magnetic anisotropy energy increases from 1.9 mJ m(-2) for 3 Fe layers up to 3.0 mJ m(-2) for 11 Fe layers. PMID:26987845

  3. Metallurgical phases and their magnetism at the interface of nanoscale MgB2/Fe layered structures

    NASA Astrophysics Data System (ADS)

    Sahoo, B.; Keune, W.; Kuncser, V.; Becker, H.-W.; Röhlsberger, R.

    2011-11-01

    We report on the characterization of metallurgical phases and their magnetism at the interfaces of nanoscale MgB2/Fe layered structures. MgB2/57Fe multilayers with varying layer thicknesses were prepared by vacuum deposition and investigated, before and after annealing by electrical resistance measurements, x-ray diffraction and 57Fe conversion-electron Mössbauer spectroscopy (CEMS) down to 5 K. Interfacial Fe-B phases, such as Fe2B, were identified by CEMS. A superparamagnetic-to-ferromagnetic transition is observed with increasing 57Fe film thickness. Ultrahigh vacuum annealing at 500 °C of the multilayers leads to strong diffusion of Fe atoms into the boundary regions of the MgB2 layers. MgB2 in the as-grown multilayers is non-superconducting. Structural disorder and the effect of Fe interdiffusion contribute to the suppression of superconductivity in the MgB2 films of all the as-grown multilayers and the thinner annealed multilayers. However, an annealed MgB2/57Fe/MgB2 trilayer with thicker (500 Å) MgB2 layers is observed to be superconducting with an onset temperature of 25 K. At 5 K, the annealed trilayer can be conceived as being strongly chemically modulated, consisting of two partially Fe-doped superconducting MgB2 layers separated by an interdiffused weakly magnetic Fe-B interlayer, which is characterized by a low hyperfine magnetic field Bhf of ˜11 T. This chemically modulated layer structure of the trilayer after annealing was verified by Rutherford backscattering.

  4. Metallurgical phases and their magnetism at the interface of nanoscale MgB2/Fe layered structures.

    PubMed

    Sahoo, B; Keune, W; Kuncser, V; Becker, H-W; Röhlsberger, R

    2011-11-30

    We report on the characterization of metallurgical phases and their magnetism at the interfaces of nanoscale MgB(2)/Fe layered structures. MgB(2)/(57)Fe multilayers with varying layer thicknesses were prepared by vacuum deposition and investigated, before and after annealing by electrical resistance measurements, x-ray diffraction and (57)Fe conversion-electron Mössbauer spectroscopy (CEMS) down to 5 K. Interfacial Fe-B phases, such as Fe(2)B, were identified by CEMS. A superparamagnetic-to-ferromagnetic transition is observed with increasing (57)Fe film thickness. Ultrahigh vacuum annealing at 500 °C of the multilayers leads to strong diffusion of Fe atoms into the boundary regions of the MgB(2) layers. MgB(2) in the as-grown multilayers is non-superconducting. Structural disorder and the effect of Fe interdiffusion contribute to the suppression of superconductivity in the MgB(2) films of all the as-grown multilayers and the thinner annealed multilayers. However, an annealed MgB(2)/(57)Fe/MgB(2) trilayer with thicker (500 Å) MgB(2) layers is observed to be superconducting with an onset temperature of 25 K. At 5 K, the annealed trilayer can be conceived as being strongly chemically modulated, consisting of two partially Fe-doped superconducting MgB(2) layers separated by an interdiffused weakly magnetic Fe-B interlayer, which is characterized by a low hyperfine magnetic field B(hf) of ∼11 T. This chemically modulated layer structure of the trilayer after annealing was verified by Rutherford backscattering.

  5. Discovery of New Al-Cu-Fe Minerals in the Khatyrka CV3 Meteorite

    NASA Astrophysics Data System (ADS)

    Ma, C.; Lin, C.; Bindi, L.; Steinhardt, P. J.

    2016-08-01

    Our nanomineralogy investigation of Khatyrka has revealed two new alloy minerals (AlCu with a Pm-3m CsCl structure and Al3Fe with a C2/m structure) and associated icosahedrite (quasicrystal Al63Cu26Fe11 with a five-fold symmetry) in section 126A of USNM 7908.

  6. MgFe{sub 2}O{sub 4} pigment obtained at low temperature

    SciTech Connect

    Candeia, R.A. . E-mail: roberlucia@yahoo.com.br; Souza, M.A.F.; Bernardi, M.I.B.; Maestrelli, S.C.; Santos, I.M.G.; Souza, A.G.; Longo, E.

    2006-01-05

    This work had the objective of studying the pigment MgFe{sub 2}O{sub 4} obtained by the polymeric precursor method, which is based on the formation of a polymeric resin, followed by a heat treatment in order to obtain the final oxide. The powders were calcined between 500 and 1100 deg. C, and characterized by thermal analysis, X-ray diffraction, nitrogen adsorption, scanning electronic microscopy and diffuse reflectance. The pigment is single phase, with a cubic system and space group Fd3m (2 2 7). A low temperature synthesis was possible, with a crystalline material after heat treatment at 800 deg. C. The colors obtained varied, according to the crystallization of the MgFe{sub 2}O{sub 4}.

  7. First-principles investigation of mechanical behavior of B2 type aluminides: FeAl and NiAl

    SciTech Connect

    Fu, C.L.; Yoo, M.H.

    1990-01-01

    First-principles calculations of the elastic constants, shear fault energies, and cleavage strength of NiAl and FeAl are presented. For NiAl, we find that the dissociation of {l angle}111{r angle} superdislocation into partial dislocations is unlikely, due to a high antiphase boundary energy and a weak repulsive elastic force between partial dislocations. FeAl has a high ideal cleavage strength as a result of the directional d-bond formation at the Fe sites. The strong ordering behavior of NiAl is explained in terms of the Al-to-Ni charge transfer and the repulsive interaction between Al atoms. The spontaneous glide decomposition of the {l angle}111{r angle} superdislocation in NiAl is also discussed. 8 refs., 2 figs., 2 tabs.

  8. Phase relation of C-Mg-Fe-Si-O system under various oxygen fugacity conditions at high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Takahashi, S.; Ohtani, E.; Terasaki, H.; Ito, Y.; Shibazaki, Y.; Ishii, M.; Funakoshi, K.; Higo, Y.

    2010-12-01

    Many exoplanets have been found recently based on the spectroscopic observation. A carbon-rich circumstellar gas was reported to exist around “beta-Pictoris”, which has an exoplanet (Roberge et al., 2006). In such gas, carbon-enriched planet, “carbon-planet” may be formed. Carbon-bearing phase, such as carbide, carbonate, graphite and diamond are likely to compose the carbon-planet interior. Therefore, it is important to investigate phase relations of carbon-rich systems under high pressure conditions. In this study, C-enriched Mg-Si-Fe-O-C system was investigated at high pressure and temperature in order to understand the internal structure of the carbon-planet. Phase relations were studied based on 2 series of experiments; (I)textural observation and chemical analysis of the recovered sample from 4 GPa and 1873K and (II)in situ X-ray diffraction experiments under high pressure and temperature. For the starting materials, we used several different mineral assemblages, as shown below: (i) MgCO3 + Fe + Si + C, (ii) (Mg1.8,Fe0.2)SiO4 + Fe + SiO2 + C, (iii) (Mg1.8,Fe0.2)SiO4 + Fe + Si + C, (iv) MgO + Fe + SiO2 + C, (v) MgO + Fe + Si + C. Oxygen fugacity (fO2) of the sample vaies dependign on these assembleges due to different O amount in the starting materials. The sample was enclosed in graphite or MgO capsule. MgO capsule enables us to estimate fO2 in the sample based on the FeO content of the capsule contacting with the samples. Chemical analyses of the recovered samples were performed using electron microprobe. In situ X-ray diffraction experiments were conducted at 4 GPa and up to 1873 K at BL04B1 beamline, SPring-8 synchrotron facility. Different mineral assemblages and their compositions were observed in the recovered samples depending on the redox condition of the sample. The compositions of metallic melt phases changes from Fe-C composition (C = 6.9~8.2 wt.%) in oxidizing conditions (ΔIW = -2.4 ~ -1.7) to Fe-Si composition (Si = 18 wt.%) in the more

  9. Self-learning kinetic Monte Carlo simulations of Al diffusion in Mg.

    PubMed

    Nandipati, Giridhar; Govind, Niranjan; Andersen, Amity; Rohatgi, Aashish

    2016-04-20

    Vacancy-mediated diffusion of an Al atom in the pure Mg matrix is studied using the atomistic, on-lattice self-learning kinetic Monte Carlo (SLKMC) method. Activation barriers for vacancy-Mg and vacancy-Al atom exchange processes are calculated on the fly using the climbing image nudged-elastic-band method and binary Mg-Al modified embedded-atom method interatomic potential. Diffusivities of an Al atom obtained from SLKMC simulations show the same behavior as observed in experimental and theoretical studies available in the literature; that is, an Al atom diffuses faster within the basal plane than along the c-axis. Although the effective activation barriers for an Al atom diffusion from SLKMC simulations are close to experimental and theoretical values, the effective prefactors are lower than those obtained from experiments. We present all the possible vacancy-Mg and vacancy-Al atom exchange processes and their activation barriers identified in SLKMC simulations. A simple mapping scheme to map an HCP lattice onto a simple cubic lattice is described, which enables simulation of the HCP lattice using the on-lattice framework. We also present the pattern recognition scheme which is used in SLKMC simulations to identify the local Al atom configuration around a vacancy.

  10. Self-learning kinetic Monte Carlo simulations of Al diffusion in Mg

    NASA Astrophysics Data System (ADS)

    Nandipati, Giridhar; Govind, Niranjan; Andersen, Amity; Rohatgi, Aashish

    2016-04-01

    Vacancy-mediated diffusion of an Al atom in the pure Mg matrix is studied using the atomistic, on-lattice self-learning kinetic Monte Carlo (SLKMC) method. Activation barriers for vacancy-Mg and vacancy-Al atom exchange processes are calculated on the fly using the climbing image nudged-elastic-band method and binary Mg-Al modified embedded-atom method interatomic potential. Diffusivities of an Al atom obtained from SLKMC simulations show the same behavior as observed in experimental and theoretical studies available in the literature; that is, an Al atom diffuses faster within the basal plane than along the c-axis. Although the effective activation barriers for an Al atom diffusion from SLKMC simulations are close to experimental and theoretical values, the effective prefactors are lower than those obtained from experiments. We present all the possible vacancy-Mg and vacancy-Al atom exchange processes and their activation barriers identified in SLKMC simulations. A simple mapping scheme to map an HCP lattice onto a simple cubic lattice is described, which enables simulation of the HCP lattice using the on-lattice framework. We also present the pattern recognition scheme which is used in SLKMC simulations to identify the local Al atom configuration around a vacancy.

  11. Fabrication of MgFe2O4/MoS2 Heterostructure Nanowires for Photoelectrochemical Catalysis.

    PubMed

    Fan, Weiqiang; Li, Meng; Bai, Hongye; Xu, Dongbo; Chen, Chao; Li, Chunfa; Ge, Yilin; Shi, Weidong

    2016-02-16

    A novel one-dimensional MgFe2O4/MoS2 heterostructure has been successfully designed and fabricated. The bare MgFe2O4 was obtained as uniform nanowires through electrospinning, and MoS2 thin film appeared on the surface of MgFe2O4 after further chemical vapor deposition. The structure of the MgFe2O4/MoS2 heterostructure was systematic investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrometry (XPS), and Raman spectra. According to electrochemical impedance spectroscopy (EIS) results, the MgFe2O4/MoS2 heterostructure showed a lower charge-transfer resistance compared with bare MgFe2O4, which indicated that the MoS2 played an important role in the enhancement of electron/hole mobility. MgFe2O4/MoS2 heterostructure can efficiently degrade tetracycline (TC), since the superoxide free-radical can be produced by sample under illumination due to the active species trapping and electron spin resonance (ESR) measurement, and the optimal photoelectrochemical degradation rate of TC can be achieved up to 92% (radiation intensity: 47 mW/cm(2), 2 h). Taking account of its unique semiconductor band gap structure, MgFe2O4/MoS2 can also be used as an photoelectrochemical anode for hydrogen production by water splitting, and the hydrogen production rate of MgFe2O4/MoS2 was 5.8 mmol/h·m(2) (radiation intensity: 47 mW/cm(2)), which is about 1.7 times that of MgFe2O4. PMID:26797320

  12. Fabrication of MgFe2O4/MoS2 Heterostructure Nanowires for Photoelectrochemical Catalysis.

    PubMed

    Fan, Weiqiang; Li, Meng; Bai, Hongye; Xu, Dongbo; Chen, Chao; Li, Chunfa; Ge, Yilin; Shi, Weidong

    2016-02-16

    A novel one-dimensional MgFe2O4/MoS2 heterostructure has been successfully designed and fabricated. The bare MgFe2O4 was obtained as uniform nanowires through electrospinning, and MoS2 thin film appeared on the surface of MgFe2O4 after further chemical vapor deposition. The structure of the MgFe2O4/MoS2 heterostructure was systematic investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrometry (XPS), and Raman spectra. According to electrochemical impedance spectroscopy (EIS) results, the MgFe2O4/MoS2 heterostructure showed a lower charge-transfer resistance compared with bare MgFe2O4, which indicated that the MoS2 played an important role in the enhancement of electron/hole mobility. MgFe2O4/MoS2 heterostructure can efficiently degrade tetracycline (TC), since the superoxide free-radical can be produced by sample under illumination due to the active species trapping and electron spin resonance (ESR) measurement, and the optimal photoelectrochemical degradation rate of TC can be achieved up to 92% (radiation intensity: 47 mW/cm(2), 2 h). Taking account of its unique semiconductor band gap structure, MgFe2O4/MoS2 can also be used as an photoelectrochemical anode for hydrogen production by water splitting, and the hydrogen production rate of MgFe2O4/MoS2 was 5.8 mmol/h·m(2) (radiation intensity: 47 mW/cm(2)), which is about 1.7 times that of MgFe2O4.

  13. Crystallization control for remediation of an FetO-rich CaO-SiO2-Al2O3-MgO EAF waste slag.

    PubMed

    Jung, Sung Suk; Sohn, Il

    2014-01-01

    In this work, the crystallization behavior of synthesized FetO-rich electric arc furnace (EAF) waste slags with a basicity range of 0.7 to 1.08 was investigated. Crystal growth in the melts was observed in situ using a confocal laser scanning microscope, and a delayed crystallization for higher-basicity samples was observed in the continuous cooling transformation and time temperature transformation diagrams. This result is likely due to the polymerization of the melt structure as a result of the increased number of network-forming FeO4 and AlO4 units, as suggested by Raman analysis. The complex incorporation of Al and Fe ions in the form of AlO4 and FeO4 tetrahedral units dominant in the melt structure at a higher basicity constrained the precipitation of a magnetic, nonstoichiometric, and Fe-rich MgAlFeO4 primary phase. The growth of this spinel phase caused a clear compositional separation from amorphous phase during isothermal cooling at 1473 K leading to a clear separation between the primary and amorphous phases, allowing an efficient magnetic separation of Fe compounds from the slag for effective remediation and recycling of synthesized EAF waste slags for use in higher value-added ordinary Portland cement.

  14. Crystallization control for remediation of an FetO-rich CaO-SiO2-Al2O3-MgO EAF waste slag.

    PubMed

    Jung, Sung Suk; Sohn, Il

    2014-01-01

    In this work, the crystallization behavior of synthesized FetO-rich electric arc furnace (EAF) waste slags with a basicity range of 0.7 to 1.08 was investigated. Crystal growth in the melts was observed in situ using a confocal laser scanning microscope, and a delayed crystallization for higher-basicity samples was observed in the continuous cooling transformation and time temperature transformation diagrams. This result is likely due to the polymerization of the melt structure as a result of the increased number of network-forming FeO4 and AlO4 units, as suggested by Raman analysis. The complex incorporation of Al and Fe ions in the form of AlO4 and FeO4 tetrahedral units dominant in the melt structure at a higher basicity constrained the precipitation of a magnetic, nonstoichiometric, and Fe-rich MgAlFeO4 primary phase. The growth of this spinel phase caused a clear compositional separation from amorphous phase during isothermal cooling at 1473 K leading to a clear separation between the primary and amorphous phases, allowing an efficient magnetic separation of Fe compounds from the slag for effective remediation and recycling of synthesized EAF waste slags for use in higher value-added ordinary Portland cement. PMID:24410350

  15. Magnetotransport measurements of current induced effective fields in Ta/CoFeB/MgO

    SciTech Connect

    Zhang, Chaoliang; Yamanouchi, Michihiko Ikeda, Shoji; Sato, Hideo; Fukami, Shunsuke; Matsukura, Fumihiro; Ohno, Hideo

    2013-12-23

    We evaluate current-induced effective magnetic fields in perpendicularly magnetized Ta/CoFeB/MgO structures from the external magnetic field angle dependence of the Hall resistance. We confirm the presence of two components of effective fields. The dependence of their magnitudes on Ta thickness implies that both components are related to the spin current in Ta layer generated by the spin Hall effect.

  16. Mg/Fe FRACTIONATION IN CIRCUMSTELLAR SILICATE DUST INVOLVED IN CRYSTALLIZATION

    SciTech Connect

    Murata, K.; Takakura, T.; Chihara, H.; Koike, C.; Tsuchiyama, A.

    2009-05-10

    Infrared astronomical observations of oxygen-rich young and evolved stars show that only magnesium-rich crystalline silicates exist in circumstellar regions, and iron, one of the most important dust-forming elements, is extremely depleted. The compositional characteristic of circumstellar crystalline silicates is fundamentally different from that of primitive extraterrestrial materials in our solar system, such as chondritic meteorites and interplanetary dust particles. Amorphous silicates are ubiquitous and abundant in space, and are a promising carrier of iron. However, since the first detection of crystalline silicates, there has been an unsolved inconsistency due to differing compositions of coexisting crystalline and amorphous phases, considering that amorphous silicates have been expected to be precursors of these crystals. Here we show the first experimental evidence that Fe-depleted olivine can be formed by crystallization via thermal heating of FeO-bearing amorphous silicates under subsolidus conditions. Mg/Fe fractionation involved in crystallization makes possible to coexist Mg-rich crystalline silicates with Fe-bearing amorphous silicates around stars.

  17. Strain control magnetocrystalline anisotropy of Ta/FeCo/MgO heterostructures

    SciTech Connect

    Ong, P. V.; Kioussis, Nicholas; Amiri, P. Khalili; Wang, K. L.; Carman, Gregory P.

    2015-05-07

    Using ab initio electronic structure calculations, we have investigated the effect of epitaxial strain on magnetocrystalline anisotropy (MCA) of Ta/FeCo/MgO heterostructure. At small expansive strains on the FeCo layer, the system exhibits perpendicular MCA (PMA). Strain not only has a profound effect on the value of MCA but also induces a switching of magnetic easy axis. Analysis of the energy- and k-resolved distribution of orbital characters of the minority-spin band reveals that a significant contribution to PMA at zero strain arises from the spin-orbit coupling between occupied d{sub x{sup 2}−y{sup 2}} and unoccupied d{sub xy} states, derived from Fe at the FeCo/MgO interface. The strain effect is attributed to strain-induced shifts of spin-orbit coupled d-states. Our work demonstrates that strain engineering can open a viable pathway towards tailoring magnetic properties for spintronic applications.

  18. Gradiente radial de [Mg/Fe] em duas galáxias elípticas

    NASA Astrophysics Data System (ADS)

    Milone, A.; Capelato, H.

    2003-08-01

    Basicamente, são propostos dois cenários de evolução quí mio-dinâmico para os sistemas esferoidais: (i) o hierárquico através da fusão e/ou acresção de sub-sistemas com ou sem surtos de formação estelar, e (ii) o colapso monolí tico dissipativo com formação estelar interrompida por um vento galáctico. Ambos, dentro de certos limites, conseguem explicar os gradientes internos de metalicidade estelar presentes nas galáxias elí pticas bem como a relação observada entre a metalicidade central e a massa (Mg20 vs. log sv0). No entanto, nenhum prevê uma variação interna para a razão de abundâncias Mg/Fe que indiretamente define a escala temporal da formação estelar. Empregamos a espectroscopia óptica de fenda longa com a finalidade de recuperar as histórias de formação estelar, de enriquecimento quí mico e da dinâmica dentro de determinadas regiões das galáxias. Os espectros de média resolução (FWHM = 7,1 Å) e escala angular de 1,092 arcsec/pixel foram coletados com o telescópio 1,60m do OPD/LNA. Comparamos nossas medidas de linhas de absorção com resultados espectrofotométricos de modelos de populações estelares simples - mais especificamente os í ndices do Sistema Lick como Mg2, Mg b, < Fe > e Hb - a fim de se investigar as variações internas de [Fe/H], [Mg/Fe] e idade. Para duas galáxias elí pticas, NGC 1052 e NGC 7796, pertencentes a ambientes de baixa densidade, encontramos uma variação radial da razão Mg/Fe decrescente do centro para fora em regiões de 0,6 e 1 raio efetivo respectivamente. Discutimos alguns cenários de enriquecimento quí mico para estas duas galáxias.

  19. Oxidation Control of Atmospheric Plasma Sprayed FeAl Intermetallic Coatings Using Dry-Ice Blasting

    NASA Astrophysics Data System (ADS)

    Song, Bo; Dong, Shujuan; Coddet, Pierre; Hansz, Bernard; Grosdidier, Thierry; Liao, Hanlin; Coddet, Christian

    2013-03-01

    The performance of atmospheric plasma sprayed FeAl coatings has been remarkably limited because of oxidation and phase transformation during the high-temperature process of preparation. In the present work, FeAl intermetallic coatings were prepared by atmospheric plasma spraying combined with dry-ice blasting. The microstructure, oxidation, porosity, and surface roughness of FeAl intermetallic coatings were investigated. The results show that a denser FeAl coating with a lower content of oxide and lower degree of phase transformation can be achieved because of the cryogenic, the cleaning, and the mechanical effects of dry-ice blasting. The surface roughness value decreased, and the adhesive strength of FeAl coating increased after the application of dry-ice blasting during the atmospheric plasma spraying process. Moreover, the microhardness of the FeAl coating increased by 72%, due to the lower porosity and higher dislocation density.

  20. Structural investigation of the (010) surface of the Al13 Fe4 catalyst.

    PubMed

    Ledieu, J; Gaudry, É; Loli, L N Serkovic; Villaseca, S Alarcón; de Weerd, M-C; Hahne, M; Gille, P; Grin, Y; Dubois, J-M; Fournée, V

    2013-02-15

    We have investigated the structure of the Al(13)Fe(4)(010) surface using both experimental and ab initio computational methods. The results indicate that the topmost surface layers correspond to incomplete puckered (P) planes present in the bulk crystal structure. The main building block of the corrugated termination consists of two adjacent pentagons of Al atoms, each centered by a protruding Fe atom. These motifs are interconnected via additional Al atoms referred to as "glue" atoms which partially desorb above 873 K. The surface structure of lower atomic density compared to the bulk P plane is explained by a strong Fe-Al-Fe covalent polar interaction that preserves intact clusters at the surface. The proposed surface model with identified Fe-containing atomic ensembles could explain the Al(13)Fe(4) catalytic properties recently reported in line with the site-isolation concept [M. Armbrüster et al., Nat. Mater. 11, 690 (2012)]. PMID:25166385

  1. Structural investigation of the (010) surface of the Al13 Fe4 catalyst.

    PubMed

    Ledieu, J; Gaudry, É; Loli, L N Serkovic; Villaseca, S Alarcón; de Weerd, M-C; Hahne, M; Gille, P; Grin, Y; Dubois, J-M; Fournée, V

    2013-02-15

    We have investigated the structure of the Al(13)Fe(4)(010) surface using both experimental and ab initio computational methods. The results indicate that the topmost surface layers correspond to incomplete puckered (P) planes present in the bulk crystal structure. The main building block of the corrugated termination consists of two adjacent pentagons of Al atoms, each centered by a protruding Fe atom. These motifs are interconnected via additional Al atoms referred to as "glue" atoms which partially desorb above 873 K. The surface structure of lower atomic density compared to the bulk P plane is explained by a strong Fe-Al-Fe covalent polar interaction that preserves intact clusters at the surface. The proposed surface model with identified Fe-containing atomic ensembles could explain the Al(13)Fe(4) catalytic properties recently reported in line with the site-isolation concept [M. Armbrüster et al., Nat. Mater. 11, 690 (2012)].

  2. Temperature variation of the size effect in dilute AlMg and AlCa alloys: Measurement and theory

    NASA Astrophysics Data System (ADS)

    Gilder, H. M.; Asty, M.; Audit, Ph.

    1980-12-01

    Optical-interferometric-differential-length and x-ray lattice-parameter measurements performed at low temperatures in dilute AlMg and AlCa alloys indicate that the temperature variation of the size effect corresponds to a relatively large difference between the intrinsic coefficient of thermal expansion βi of the solute atom structure and that, β, of the solvent. This result is another example of the surprising expansive properties of point defects previously described by Gilder and co-workers (high-temperature vacancy diffusion) and more recently by Ganne (low-temperature dilatometry on irradiated specimens). Specifically, in the temperature range 0.2Mg)β~3 and βi(Ca)β~-4. This, as well as the fact that the sign of the change in the coefficient of thermal expansion Δβ of the host metal caused by the introduction of the solute atom is positive for Mg and negative for Ca, indicates that solute-solvent valence effects play a minor role in determining the coefficient of thermal expansion of the dilute alloy. It is also found, to within the experimental precision, that Δβ(Mg) and Δβ(Ca) are temperature independent, suggesting a type of Matthiessen's rule for thermal expansion. A model calculation of the size effect and its temperature variation in the infinitely dilute alloy is presented. The volume-dependent forces are treated by means of a term describing the elastic energy associated with the solute-solvent volume misfit, whereas the temperature-dependent potential of Dagens et al. is used to calculate the pairwise interaction between the solvent ions and the solute ion. Good agreement with the experimental data is obtained for the size effect in both AlMg and AlCa. The calculated values of Δβ(Mg)Ci, Ci being the solute concentration, and βi(Mg) fall between the measured values in the two AlMg alloys studied. The calculation of Δβ(Ca)Ci and βi(Ca) is not possible due to a lack of elastic-constants data for pure, metallic

  3. New structure and spin state of iron-rich (Mg,Fe)SiO[subscript 3] post-perovskite

    SciTech Connect

    Yamanaka, T.; Mao, W.L.; Mao, H.-K.; Hemley, R.J.; Shen, G.

    2010-05-24

    There was a discrepancy between the seismic tomography and the elastic property of MgSiO{sub 3} perovskite at near the D{double_prime} zone and core boundary. Since a discovery of post-perovskite (ppv) of MgSiO{sub 3}, many investigations have made to explain the presence of low seismic velocity of the lower mantle and D{double_prime} zone. However, precise experimental structure analysis of ppv-(Mg{sub 1-x}Fe{sub x})SiO{sub 3} has never been reported because of the experimental difficulty. Fe and Mg cation distribution and ordering in ppv-(Mg,Fe)SiO{sub 3} in consideration of spins states are significant subject in lower mantle electronic and magnetic states. The present experiment aims X-ray emission study and structure analysis by Rietveld profile fitting of ppv-(Mg{sub 0.6},Fe{sub 0.4})SiO{sub 3} by the precise powder diffraction measurement. Monte Carlo calculation proposed the reliable structures of iron-rich phase of ppv-(Mg,Fe)SiO{sub 3}: Pmmn, Pmma, and Cm2m and Cmcm proposed by. The best-fit structure model with the highest reliability in the Rietveld fitting of ppv-(Mg{sub 0.6}Fe{sub 0.4})SiO{sub 3} is the structure of space group Pmma, in which Fe and Mg occupy two different sites of M1 and M2: the site occupancies are (Fe{sub 0.25}Mg{sub 0.75}) in the larger M1 site and (Fe{sub 0.55}, Mg{sub 0.45}) in the smaller M2 site. The two-site model is consistence with the previous results of X-ray emission and X-ray Moessbauer experiments.

  4. CWPO of 4-CP and industrial wastewater with Al-Fe pillared clays.

    PubMed

    Molina, C B; Zazo, J A; Casas, J A; Rodriguez, J J

    2010-01-01

    Catalysts based on pillared clays with Al-Fe have been synthesised from a commercial bentonite and tested for catalytic wet peroxide oxidation (CWPO) of aqueous 4-Chlorophenol (4-CP) solution and industrial wastewater from cosmetics manufacture. The effect of the synthesis procedure, the iron load and reaction temperature on the catalytic activity was studied using 4-CP as target compound. A lower temperature in the preparation of the pillaring solution, as well as a higher Fe load, gave rise to a higher catalytic activity, but also a higher leaching of the active phase. The best catalyst, in terms of catalytic activity, was also tested for treating cosmetic wastewater by CWPO. Experiments were carried out at 90 degrees C and atmospheric pressure and the influence of Fe load, catalyst concentration and H(2)O(2)/COD ratio (between 0.5 and 2 times the stoichiometric ratio) were analysed. Higher values of these parameters favour COD reduction. The Fe leaching in all cases was lower than 1.2 mg/L, indicating that these catalysts have a high stability under these experimental conditions. PMID:20389016

  5. Thermoelectric properties of Al doped Mg{sub 2}Si material

    SciTech Connect

    Kaur, Kulwinder Kumar, Ranjan; Rani, Anita

    2015-08-28

    In the present paper we have calculated thermoelectric properties of Al doped Mg{sub 2}Si material (Mg{sub 2−x}Al{sub x}Si, x=0.06) using Pseudo potential plane wave method based on DFT and Semi classical Boltzmann theory. The calculations showed n-type conduction, indicating that the electrical conduction are due to electron. The electrical conductivity increasing with increasing temperature and the negative value of Seebeck Coefficient also show that the conduction is due to electron. The thermal conductivity was increased slightly by Al doping with increasing temperature due to the much larger contribution of lattice thermal conductivity over electronic thermal conductivity.

  6. Effect of nitrogen upon structural and magnetic properties of FePt in FePt/AlN multilayer structures

    SciTech Connect

    Gao, Tenghua Zhang, Cong; Sannomiya, Takumi; Muraishi, Shinji; Nakamura, Yoshio; Shi, Ji

    2014-09-01

    This paper investigates the effect of the addition of nitrogen in FePt layers for ultrathin FePt/AlN multilayer structures. X-ray diffraction results reveal that a compressive stress relaxation occurs after annealing owing to the release of interstitial nitrogen atoms in the FePt layers. The introduction of nitrogen also induces a large in-plane compressive strain during grain growth not seen in FePt deposited without nitrogen. This strain is considered to decrease the driving force for (111) grain growth and FePt ordering.

  7. The thermal equation of state of (Mg, Fe)SiO3 bridgmanite (perovskite) and implications for lower mantle structures

    NASA Astrophysics Data System (ADS)

    Wolf, Aaron S.; Jackson, Jennifer M.; Dera, Przemeslaw; Prakapenka, Vitali B.

    2015-11-01

    The high-pressure/high-temperature equation of state (EOS) of synthetic 13% Fe-bearing bridgmanite (Mg silicate perovskite) is measured using powder X-ray diffraction in a laser-heated diamond anvil cell with a quasi-hydrostatic neon pressure medium. We compare these results, which are consistent with previous 300 K sound speed and compression studies, with a reanalysis of Fe-free Mg end-member data from Tange et al. (2012) to determine the effect of iron on bridgmanite's thermoelastic properties. EOS parameters are incorporated into an ideal lattice mixing model to probe the behavior of bridgmanite at deep mantle conditions. With this model, a nearly pure bridgmanite mantle composition is shown to be inconsistent with density and compressibility profiles of the lower mantle. We also explore the buoyant stability of bridgmanite over a range of temperatures and compositions expected for Large Low-Shear Velocity Provinces, concluding that bridgmanite-dominated thermochemical piles are more likely to be passive dense layers externally supported by convection, rather than internally supported metastable domes. The metastable dome scenario is estimated to have a relative likelihood of only 4-7%, given the narrow range of compositions and temperatures consistent with seismic constraints. If buoyantly supported, such structures could not have remained stable with greater thermal contrast early in Earth's history, ruling out formation scenarios involving a large concentration of heat producing elements.

  8. Magnetostrictive behaviors of Fe-Al(001) single-crystal films under rotating magnetic fields

    NASA Astrophysics Data System (ADS)

    Kawai, Tetsuroh; Abe, Tatsuya; Ohtake, Mitsuru; Futamoto, Masaaki

    2016-05-01

    Magnetostrictive behaviors of Fe100-x - Alx(x = 0 - 30 at.%)(001) single-crystal films under rotating magnetic fields are investigated along the two different crystallographic orientations, [100] and [110]. The behaviors of Fe and Fe90Al10 films show bath-tub like waveform along [100], easy magnetization axis, and triangular waveform along [110], hard magnetization axis, with respect to their four-fold magnetic anisotropy. On the other hand, the behaviors of Fe80Al20 film are different from those of Fe or Fe90Al10 film. The output of the film along [100] shows a strong magnetic field dependence. The Fe70Al30 film shows similar magnetostrictive behaviors along both [100] and [110] reflecting its magnetic properties, which are almost same for the both directions. The growth of ordered phase (B2) in Fe80Al20 and Fe70Al30 films is considered to have affected their magnetostrictive behaviors. The Al content dependence on λ100 and λ111 values shows similar tendency to that reported for the bulk samples but the values are slightly different. The Fe90Al10(001) single-crystal film shows a large magnetostriction along [100] under a very small magnetic field of 0.02 kOe, which is comparable to the saturated one, and changes the value abruptly in relation to the angle of applied magnetic field.

  9. Single-crystal structure determination of (Mg,Fe)SiO3 postperovskite.

    PubMed

    Zhang, Li; Meng, Yue; Dera, Przemyslaw; Yang, Wenge; Mao, Wendy L; Mao, Ho-Kwang

    2013-04-16

    Knowledge of the structural properties of mantle phases is critical for understanding the enigmatic seismic features observed in the Earth's lower mantle down to the core-mantle boundary. However, our knowledge of lower mantle phase equilibria at high pressure (P) and temperature (T) conditions has been based on limited information provided by powder X-ray diffraction technique and theoretical calculations. Here, we report the in situ single-crystal structure determination of (Mg,Fe)SiO3 postperovskite (ppv) at high P and after temperature quenching in a diamond anvil cell. Using a newly developed multigrain single-crystal X-ray diffraction analysis technique in a diamond anvil cell, crystallographic orientations of over 100 crystallites were simultaneously determined at high P in a coarse-grained polycrystalline sample containing submicron ppv grains. Conventional single-crystal structural analysis and refinement methods were applied for a few selected ppv crystallites, which demonstrate the feasibility of the in situ study of crystal structures of submicron crystallites in a multiphase polycrystalline sample contained within a high P device. The similarity of structural models for single-crystal Fe-bearing ppv (~10 mol% Fe) and Fe-free ppv from previous theoretical calculations suggests that the Fe content in the mantle has a negligible effect on the crystal structure of the ppv phase.

  10. Selective oxidation catalysts obtained by immobilization of iron(III) porphyrins on thiosalicylic acid-modified Mg-Al layered double hydroxides.

    PubMed

    de Freitas Castro, Kelly Aparecida Dias; Wypych, Fernando; Antonangelo, Ariana; Mantovani, Karen Mary; Bail, Alesandro; Ucoski, Geani Maria; Ciuffi, Kátia Jorge; Cintra, Thais Elita; Nakagaki, Shirley

    2016-09-15

    Nitrate-intercalated Mg-Al layered double hydroxides (LDHs) were synthesized and exfoliated in formamide. Reaction of the single layer suspension with thiosalicylic acid under different conditions afforded two types of solids: LDHA1, in which the outer surface was modified with the anion thiosalicylate, and LDHA2, which contained the anion thiosalicylate intercalated between the LDH layers. LDHA1 and LDHA2 were used as supports to immobilize neutral (FeP1 and FeP2) and anionic (FeP3) iron(III) porphyrins. For comparison purposes, the iron(III) porphyrins (FePs) were also immobilized on LDH intercalated with nitrate anions obtained by the co-precipitation method. Chemical modification of LDH facilitated immobilization of the FePs through interaction of the functionalizing groups in LDH with the peripheral substituents on the porphyrin ring. The resulting FePx-LDHAy solids were characterized by X-ray diffraction (powder) and UV-Vis and EPR spectroscopies and were investigated as catalysts in the oxidation of cyclooctene and cyclohexane. The immobilized neutral FePs and their homogeneous counterparts gave similar product yields in the oxidation of cyclooctene, suggesting that immobilization of the FePs on the thiosalicylate-modified LDHs only supported the catalyst species without interfering in the catalytic outcome. On the other hand, in the oxidation of cyclohexane, the thiosalicylate anions on the outer surface of LDHA1 or intercalated between the LDHA2 layers influenced the catalytic activity of FePx-LDHAy, leading to different efficiency and selectivity results. FeP1-LDHA2 performed the best (29.6% alcohol yield) due to changes in the polarity of the surface of the support and the presence of FeP1. Interestingly, FeP1 also performed better in solution as compared to the other FePs. Finally, it was possible to recycle FeP1-LDHA2 at least three times.

  11. Reduction Kinetics of Electric Arc Furnace Oxidizing Slag by Al-Fe Alloy

    NASA Astrophysics Data System (ADS)

    Lee, Jaehong; Oh, Joon Seok; Lee, Joonho

    2016-07-01

    Effects of temperature and slag basicity on the reduction rate of iron oxide in molten synthetic electric arc furnace oxidizing slag by Al-40 wt.%Fe alloy was investigated. An alloy sample was dropped into molten slag in an MgO crucible. When the initial slag temperature was 1723 K, there was no reduction. However, when the initial slag temperature was 1773 K and the slag basicity was 1.1, the reduction was initiated and the temperature of the slag rapidly increased. When the slag basicity was 1.1, increasing the initial slag temperature from 1773 K to 1823 K increases the reaction rate. As the slag basicity increased from 1.1 to 1.4 at 1773 K, the reaction rate increased. From SEM analysis, it was found that an Al2O3 or a spinel phase at the slag-metal interface inhibited the reaction at a lower temperature and a lower slag basicity.

  12. Reduction Kinetics of Electric Arc Furnace Oxidizing Slag by Al-Fe Alloy

    NASA Astrophysics Data System (ADS)

    Lee, Jaehong; Oh, Joon Seok; Lee, Joonho

    2016-09-01

    Effects of temperature and slag basicity on the reduction rate of iron oxide in molten synthetic electric arc furnace oxidizing slag by Al-40 wt.%Fe alloy was investigated. An alloy sample was dropped into molten slag in an MgO crucible. When the initial slag temperature was 1723 K, there was no reduction. However, when the initial slag temperature was 1773 K and the slag basicity was 1.1, the reduction was initiated and the temperature of the slag rapidly increased. When the slag basicity was 1.1, increasing the initial slag temperature from 1773 K to 1823 K increases the reaction rate. As the slag basicity increased from 1.1 to 1.4 at 1773 K, the reaction rate increased. From SEM analysis, it was found that an Al2O3 or a spinel phase at the slag-metal interface inhibited the reaction at a lower temperature and a lower slag basicity.

  13. Microstructural evolution in Al-Zn-Mg-Cu-Sc-Zr alloys during short-time homogenization

    NASA Astrophysics Data System (ADS)

    Liu, Tao; He, Chun-nian; Li, Gen; Meng, Xin; Shi, Chun-sheng; Zhao, Nai-qin

    2015-05-01

    Microstructural evolution in a new kind of aluminum (Al) alloy with the chemical composition of Al-8.82Zn-2.08Mg-0.80Cu-0.31Sc-0.3Zr was investigated. It is found that the secondary phase MgZn2 is completely dissolved into the matrix during a short homogenization treatment (470°C, 1 h), while the primary phase Al3(Sc,Zr) remains stable. This is due to Sc and Zr additions into the Al alloy, high Zn/Mg mass ratio, and low Cu content. The experimental findings fit well with the results calculated by the homogenization diffusion kinetics equation. The alloy shows an excellent mechanical performance after the short homogenization process followed by hot-extrusion and T6 treatment. Consequently, a good combination of low energy consumption and favorable mechanical properties is obtained.

  14. Concentric nano rings observed on Al-Cu-Fe microspheres

    NASA Astrophysics Data System (ADS)

    Li, Chunfei; Wang, Limin; Hampikian, Helen; Bair, Matthew; Baker, Andrew; Hua, Mingjian; Wang, Qiongshu; Li, Dingqiang

    2016-05-01

    It is well known that when particle size is reduced, surface effect becomes important. As a result, micro/nanoparticles tend to have well defined geometric shapes to reduce total surface energy, as opposed to the irregular shapes observed in most bulk materials. The surface of such micro/nanostructures are smooth. Any deviation from a smooth surface implies an increased surface energy which is not energetically favorable. Here, we report an observation of spherical particles in an alloy of Al65Cu20Fe15 nominal composition prepared by arc melting. Such spherical particles stand out from those reported so far due to the decoration of concentric nanorings on the surface. Three models for the formation of these concentric ring patterns are suggested. The most prominent ones assume that the rings are frozen features of liquid motion which could open the door to investigate the kinetics of liquid motion on the micro/nanometer scale.

  15. Microstructure Evolution in Al-Cu-Fe Quasicrystalline Thin Films

    NASA Astrophysics Data System (ADS)

    Widjaja, Edy; Marks, Laurence

    2003-03-01

    Transmission Electron Microscopy (TEM) was performed to study the microstructure evolution in Al-Cu-Fe quasicrystalline thin films. Thin films were grown by magnetron sputtering on sodium chloride crystals which were subsequently dissolved in water to acquire free-standing films. Nanocrystalline films were found in the as-deposited sample. When annealed at 400oC the films changed to metastable crystalline phases that transformed into icosahedral phases upon further annealing at 500oC. TEM imaging combined with electron diffraction revealed various features associated with the phase evolution in the crystalline-quasicrystalline phase transformation. Some grains in the film functioned as sacrificial grains allowing others to grow into icosahedral phases. Elements near the boundary of the sacrificial grains diffused to form the icosahedral phases, resulting in fragments in the center of the grain. The oxide layer of the film was amorphous aluminum oxide that exhibited poor adhesion to the quasicrystalline films.

  16. Characterization of Co2FeAl nanowires

    NASA Astrophysics Data System (ADS)

    Sapkota, Keshab R.; Pegg, I. L.; Philip, J.

    2011-03-01

    Heusler alloy, Co 2 FeAl (CFA) is a potentially useful material in the field of spintronics due to its high spin polarization. The CFA nanowires are grown for the first time by the electrospinning method. The diameters of the wires formed are ranging from 80 -- 100 nm. The structural characterization of the nanowires is done using X-Ray diffraction and Raman spectroscopy. The nanowires exhibit cubic structure with a lattice constant, a = 2.44 Å. Parallel arrays of nanowires are grown for magnetic characterization using electric field applied at the collector plate. The nanowires exhibit ferromagnetic behavior with a Curie temperature higher than 400 K. Nanoscale devices are fabricated with single CFA nanowire to understand the magnetotransport properties. This work has been supported by funding from NSF under CAREER Grant No. ECCS-0845501 and NSF-MRI, DMR-0922997.

  17. Spin Polarization of Mg-23 in Mg-24 + Au, Cu and Al Collisions at 91 A MeV

    NASA Technical Reports Server (NTRS)

    Matsuta, K.; Fukuda, S.; Izumikawa, T.; Tanigaki, M.; Fukuda, M.; Nakazato, M.; Mihara, M.; Onishi, T.; Yamaguchi, T.; Miyake, T.

    1994-01-01

    Spin polarization of beta-emitting fragment Mg-23(I(sup pi) = 3/2(sup +), T(sub 1/2 = l1.3 s) produced through the projectile fragmentation process in Mg-24 + Au, Cu and Al collisions has been observed at 91 AMeV. General trend in the observed momentum dependence of polarization is reproduced well qualitatively by a simple fragmentation model based on the participant-spectator picture, for heavy and light targets. However the polarization behavior differs from this model in tern of zero crossing momentum, which become prominent in the case of Cu target, where the polarization is not monotone function of the fragment momentum.

  18. Effects of an Al3+- and Mg2+-containing antacid, ferrous sulfate, and calcium carbonate on the absorption of nemonoxacin (TG-873870) in healthy Chinese volunteers

    PubMed Central

    Zhang, Yi-fan; Dai, Xiao-jian; Wang, Ting; Chen, Xiao-yan; Liang, Li; Qiao, Hua; Tsai, Cheng-yuan; Chang, Li-wen; Huang, Ping-ting; Hsu, Chiung-yuan; Chang, Yu-ting; Tsai, Chen-en; Zhong, Da-fang

    2014-01-01

    Aim: To evaluate the effects of an Al3+- and Mg2+-containing antacid, ferrous sulfate, and calcium carbonate on the absorption of nemonoxacin in healthy humans. Methods: Two single-dose, open-label, randomized, crossover studies were conducted in 24 healthy male Chinese volunteers (12 per study). In Study 1, the subjects orally received nemonoxacin (500 mg) alone, or an antacid (containing 318 mg of Al3+ and 496 mg of Mg2+) plus nemonoxacin administered 2 h before, concomitantly or 4 h after the antacid. In Study 2, the subjects orally received nemonoxacin (500 mg) alone, or nemonoxacin concomitantly with ferrous sulfate (containing 60 mg of Fe2+) or calcium carbonate (containing 600 mg of Ca2+). Results: Concomitant administration of nemonoxacin with the antacid significantly decreased the area under the concentration-time curve from time 0 to infinity (AUC0–∞) for nemonoxacin by 80.5%, the maximum concentration (Cmax) by 77.8%, and urine recovery (Ae) by 76.3%. Administration of nemonoxacin 4 h after the antacid decreased the AUC0–∞ for nemonoxacin by 58.0%, Cmax by 52.7%, and Ae by 57.7%. Administration of nemonoxacin 2 h before the antacid did not affect the absorption of nemonoxacin. Administration of nemonoxacin concomitantly with ferrous sulfate markedly decreased AUC0–∞ by 63.7%, Cmax by 57.0%, and Ae by 59.7%, while concomitant administration of nemonoxacin with calcium carbonate mildly decreased AUC0–∞ by 17.8%, Cmax by 14.3%, and Ae by 18.4%. Conclusion: Metal ions, Al3+, Mg2+, and Fe2+ markedly decreased the absorption of nemonoxacin in healthy Chinese males, whereas Ca2+ had much weaker effects. To avoid the effects of Al3+ and Mg2+-containing drugs, nemonoxacin should be administered ≥2 h before them. PMID:25327812

  19. The Electronic Structure of Iron in Aluminous (Mg,Fe)SiO3 Perovskite at High-Pressures and Temperatures

    NASA Astrophysics Data System (ADS)

    Jackson, J. M.; Sturhahn, W.; Lerche, M.; Li, J.

    2006-12-01

    Knowledge of iron valences and spin states in silicate perovskite is relevant to our understanding of the physical and chemical properties of Earth's lower mantle such as transport properties, mechanical behavior, and element partitioning. Recent studies have proposed that aluminous ferromagnesium silicate perovskite (Al- Pv) is the principle sink for ferric iron in Earth's lower mantle [e.g. 1]. Also of geophysical interest is the electronic spin state of Al-Pv under lower mantle conditions. To date, simultaneous high-pressure and high- temperature measurements of the hyperfine parameters to identify the valence and spin states of iron in Al-Pv have not been reported. In this study, we have measured the electronic structure of the iron component of an aluminous Fe-bearing silicate perovskite sample, (Mg0.88Fe0.09)(Si0.94Al0.10)O3, close to a pyrolite composition, using synchrotron Mössbauer spectroscopy (SMS) and laser heated diamond anvil cells. Recent developments in SMS have enabled in situ measurements of small samples (< 10 μm) with relatively low 57Fe contents (< 10 at.%) to Mbar pressures [e.g. 2,3]. The samples were first synthesized in a multi-anvil apparatus [3], and the perovskite structure was confirmed by X-ray diffraction. The sample was loaded into a diamond anvil cell sandwiched between NaCl insulating layers. Measurements were carried out to 65 GPa and up to 2000 K at beamline 3-ID of the Advanced Photon Source. Spectra were collected before, during, and after laser heating, at each pressure point. Synchrotron Mössbauer spectra were also collected on decreasing pressure. Evaluation of the spectra provided the isomer shift (relative to stainless steel) and the quadrupole splitting of the iron component in silicate perovskite, which gives information on valence and spin states under lower mantle conditions. This work is supported by NSF through COMPRES and the U.S. DOE-BES, Office of Science, under Contract No. W-31-109-ENG-38. [1] Mc

  20. Nanostructure evolution in joining of Al and Fe nanoparticles with femtosecond laser irradiation

    SciTech Connect

    Jiao, Z.; Huang, H.; Zhou, Y. E-mail: nzhou@uwaterloo.ca; Liu, L.; Hu, A.; Duley, W.; He, P. E-mail: nzhou@uwaterloo.ca

    2014-04-07

    The joining of Al-Fe nanoparticles (NPs) by femtosecond (fs) laser irradiation is reported in this paper. Fe and Al NPs were deposited on a carbon film in vacuum via fs laser ablation. Particles were then exposed to multiple fs laser pulses at fluences between 0.5 and 1.3 mJ/cm{sup 2}. Transmission Electron Microscopy (TEM) and Electron Diffraction X-ray observations indicate that Al and Fe NPs bond to each other under these conditions. For comparison, bonding of Al to Al and Fe to Fe NPs was also investigated. The nanostructure, as observed using TEM, showed that individual Al NPs were monocrystalline while individual Fe NPs were polycrystalline prior to joining and that these structures are retained after the formation of Al-Al and Fe-Fe NPs. Al-Fe NPs produced by fs laser joining exhibited a mixed amorphous and crystalline phase at the interface. Bonding is suggested to originate from intermixing within a region of high field intensity between particles.

  1. Dual-scale phase-field simulation of Mg-Al alloy solidification

    NASA Astrophysics Data System (ADS)

    Monas, A.; Shchyglo, O.; Höche, D.; Tegeler, M.; Steinbach, I.

    2015-06-01

    Phase-field simulations of the nucleation and growth of primary α-Mg phase as well as secondary, β-phase of a Mg-Al alloy are presented. The nucleation model for α- and β-Mg phases is based on the “free growth model” by Greer et al.. After the α-Mg phase solidification we study a divorced eutectic growth of α- and β-Mg phases in a zoomed in melt channel between α-phase dendrites. The simulated cooling curves and final microstructures of α-grains are compared with experiments. In order to further enhance the resolution of the interdendritic region a high-performance computing approach has been used allowing significant simulation speed gain when using supercomputing facilities.

  2. Voltage-controlled magnetic anisotropy in Fe|MgO tunnel junctions studied by x-ray absorption spectroscopy

    SciTech Connect

    Miwa, Shinji Matsuda, Kensho; Tanaka, Kazuhito; Goto, Minori; Suzuki, Yoshishige; Kotani, Yoshinori; Nakamura, Tetsuya

    2015-10-19

    In this study, voltage-controlled magnetic anisotropy (VCMA) in Fe|MgO tunnel junctions was investigated via the magneto-optical Kerr effect, soft x-ray absorption spectroscopy, and magnetic circular dichroism spectroscopy. The Fe|MgO tunnel junctions showed enhanced perpendicular magnetic anisotropy under external negative voltage, which induced charge depletion at the Fe|MgO interface. Despite the application of voltages of opposite polarity, no trace of chemical reaction such as a redox reaction attributed to O{sup 2−} migration was detected in the x-ray absorption spectra of the Fe. The VCMA reported in the Fe|MgO-based magnetic tunnel junctions must therefore originate from phenomena associated with the purely electric effect, that is, surface electron doping and/or redistribution induced by an external electric field.

  3. The stability of Al,Fe-bearing phase H and a new pyrite-type hydroxide at high pressures

    NASA Astrophysics Data System (ADS)

    Nishi, M.; Kuwayama, Y.; Tsuchiya, J.; Irifune, T.

    2015-12-01

    Water plays an important role in the structure, dynamics, and evolution of planets because hydrogen can affect the physical properties and stabilities of constituent minerals in the planets. Since alumimous phase H (MgSiO4H2-AlOOH) is stable over the entire pressure range of the lower mantle, the hydrated subducting plate may deliver a certain amount of water into the bottom of the Earth's mantle (Tsuchiya 2013, Nishi et al. 2013, Ohira et al. 2014, Walter et al. 2015). Compositional analysis of phase H grains synthesized from natural serpentine shows the presence of the Fe component in this phase (Nishi et al., 2015). This result suggests that phase H would also form solid solutions with ɛ-FeOOH, since ɛ-FeOOH is isostructural to phase H and δ-AlOOH. Moreover, an ab initio calculation has recently predicted that the new high pressure form of AlOOH, which has pyrite-type structure, would be stabilized at pressures above 170 GPa (Tsuchiya and Tsuchiya, 2011). Although this pyrite-type hydroxide has been found in InOOH, this structure in AlOOH has not been reported by experimental studies. Here we examine the composition and stability of Al,Fe-bearing phase H using a multi-anvil apparatus combined with sintered diamond anvils. Results show that large amounts of Fe and Al are partitioned into phase H relative to bridgmanite. Fe likely affects the stability of phase H in the lower mantle. Also, we conducted high pressure experiments on pure δ-AlOOH by using laser-heated diamond anvil cell (DAC) techniques up to 200 GPa and 2,500 K. In-situ X-ray diffraction (XRD) measurements indicated that the transition from the δ-AlOOH to the pyrite-type structure occurs at high pressures above 190 GPa. Our experimental results exhibited a density reduction of 2.6 wt.% through the structural transition, and both experimental data plots and theoretical calculations showed similar compressibilities of δ-AlOOH and pyrite-type AlOOH. In recent years, hundreds of extra

  4. Evaluation of the microstructure of Al-Cu-Li-Ag-Mg Weldalite (tm) alloys, part 4

    NASA Technical Reports Server (NTRS)

    Pickens, Joseph R.; Kumar, K. S.; Brown, S. A.; Gayle, Frank W.

    1991-01-01

    Weldalite (trademark) 049 is an Al-Cu-Li-Ag-Mg alloy designed to have ultrahigh strength and to serve in aerospace applications. The alloy displays significantly higher strength than competitive alloys in both naturally aged and artificially aged tempers. The strengthening phases in such tempers have been identified to, in part, explain the mechanical properties attained. In general, the alloy is strengthened by delta prime Al3Li and Guinier-Preston (GP) zones in the naturally aged tempers. In artificially aged tempers in slightly underaged conditions, strengthening is provided by several phases including GP zones, theta prime Al2Cu, S prime Al2CuMg, T(sub 1) Al2CuLi, and possibly a new phase. In the peak strength artificially aged tempers, T(sub 1) is the predominant strengthening phase.

  5. Removal of fluoride from drinking water using tea waste loaded with Al/Fe oxides: A novel, safe and efficient biosorbent

    NASA Astrophysics Data System (ADS)

    Cai, Hui-mei; Chen, Gui-jie; Peng, Chuan-yi; Zhang, Zheng-zhu; Dong, Yang-yang; Shang, Guang-zhi; Zhu, Xiao-hui; Gao, Hong-jian; Wan, Xiao-chun

    2015-02-01

    A low-cost and highly efficient biosorbent was prepared by loading Al/Fe oxides onto tea waste and was tested for the ability to remove fluoride from drinking water. Key factors, including adsorbent dosage, initial fluoride concentration, contact time and initial pH of the biosorbent, were investigated. It was found that the solution pH played an important role in the removal of fluoride. The biosorbent combinations Tea-Al or Tea-Al-Fe could reduce the fluoride concentration to below 1.5 mg/L in the drinking water, a level which meets the drinking water standard recommended by the World Health Organization (WHO). In addition, the residual concentrations of Al and Fe in the drinking water after Tea-Al-Fe treatment were below the standards set by WHO when treatment was conducted at pH values ranging from 5.0 to 10.0. The experimental data were analyzed using two-parameter theoretical models. The maximum fluoride adsorption capacities for the original tea, Tea-Fe, Tea-Al and Tea-Al-Fe biosorbents were 3.83, 10.47, 13.79 and 18.52 mg/g, respectively. These findings demonstrate the suitability of a prepared biosorbent based on tea waste for the removal of fluoride from drinking water.

  6. Postperovskite phase equilibria in the MgSiO3-Al2O3 system.

    PubMed

    Tsuchiya, Jun; Tsuchiya, Taku

    2008-12-01

    We investigate high-P,T phase equilibria of the MgSiO(3)-Al(2)O(3) system by means of the density functional ab initio computation methods with multiconfiguration sampling. Being different from earlier studies based on the static substitution properties with no consideration of Rh(2)O(3)(II) phase, present calculations demonstrate that (i) dissolving Al(2)O(3) tends to decrease the postperovskite transition pressure of MgSiO(3) but the effect is not significant ( approximately -0.2 GPa/mol% Al(2)O(3)); (ii) Al(2)O(3) produces the narrow perovskite+postperovskite coexisting P,T area (approximately 1 GPa) for the pyrolitic concentration (x(Al2O3) approximately 6 mol%), which is sufficiently responsible to the deep-mantle D'' seismic discontinuity; (iii) the transition would be smeared (approximately 4 GPa) for the basaltic Al-rich composition (x(Al2O3) approximately 20 mol%), which is still seismically visible unless iron has significant effects; and last (iv) the perovskite structure spontaneously changes to the Rh(2)O(3)(II) with increasing the Al concentration involving small displacements of the Mg-site cations.

  7. Effects of heat treatment on the corrosion resistance of carbon steel coated with LaMgAl11O19 thermal barrier coatings

    NASA Astrophysics Data System (ADS)

    Huang, Liang-liang; Meng, Hui-min; Liang, Li-kang; Li, Sen; Shi, Jin-hui

    2015-10-01

    LaMgAl11O19 thermal barrier coatings (TBCs) were applied to carbon steels with a NiCoCrAlY bond coat by plasma spraying. The effects of heat treatment on the corrosion resistance of carbon steel coated with LaMgAl11O19 TBCs were investigated in 3.5wt% NaCl solution using polarization curves, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results show that a large number of cracks are found in the LaMgAl11O19 TBCs after the samples are heat-treated, including some through-thickness cracks. The corrosion forms of the as-sprayed and heat-treated TBCs are uniform corrosion and pitting corrosion, respectively. The as-sprayed TBCs exhibit three EIS time constants after being immersed for less than 7 d, and then a new time constant appears because of steel substrate corrosion. When the immersion time is increased to 56 d, a Warburg impedance ( W) component appears in the EIS data. The EIS data for the heat-treated TBCs exhibit only two time constants after the samples are immersed for less than 14 d, and a new time constant appears when the immersion time is increased further. The heat treatment reduces the corrosion resistance of carbon steel coated with LaMgAl11O19 TBCs. The corrosion products are primarily γ-FeOOH and Fe3O4.

  8. Use of Mg-Al oxide for boron removal from an aqueous solution in rotation: Kinetics and equilibrium studies.

    PubMed

    Kameda, Tomohito; Oba, Jumpei; Yoshioka, Toshiaki

    2016-01-01

    Mg-Al oxide prepared through the thermal treatment of [Formula: see text] intercalated Mg-Al layered double hydroxides (CO3·Mg-Al LDH) was found to remove boron (B) from an aqueous solution. B was removed by the rehydration of Mg-Al oxide accompanied by combination with [Formula: see text] . When using twice the stoichiometric quantity of Mg-Al oxide for Mg/Al = 4, the residual concentration of B dropped from 100 to 2.8 mg/L in 480 min, and for Mg/Al = 2, it decreased from 100 to 2.5 mg/L in 240 min. In both cases, the residual concentration of B was highlighted to be lower than the current Japanese effluent standards (10 mg/L). The removal of B can be explained by way of pseudo-first-order reaction kinetics. The apparent activation energy of 63.5 kJ mol(-1), calculated from the Arrhenius plot indicating that a chemical reaction dominates the removal of B by Mg-Al oxide (Mg/Al = 2). The adsorption of B acts upon a Langmuir-type phenomena. The maximum adsorption (qm) and equilibrium adsorption constants (KL) were 7.4 mmol g(-1) and 1.9 × 10(3), respectively, for Mg-Al oxide (Mg/Al = 2). [Formula: see text] in B(OH)4·Mg-Al LDH produced by the removal of B was observed to undergo anion exchange with [Formula: see text] in solution. Following regeneration, the Mg-Al oxide maintained the ability to remove B from an aqueous solution. This study has clarified the possibility of recycling Mg-Al oxide for B removal.

  9. Use of Mg-Al oxide for boron removal from an aqueous solution in rotation: Kinetics and equilibrium studies.

    PubMed

    Kameda, Tomohito; Oba, Jumpei; Yoshioka, Toshiaki

    2016-01-01

    Mg-Al oxide prepared through the thermal treatment of [Formula: see text] intercalated Mg-Al layered double hydroxides (CO3·Mg-Al LDH) was found to remove boron (B) from an aqueous solution. B was removed by the rehydration of Mg-Al oxide accompanied by combination with [Formula: see text] . When using twice the stoichiometric quantity of Mg-Al oxide for Mg/Al = 4, the residual concentration of B dropped from 100 to 2.8 mg/L in 480 min, and for Mg/Al = 2, it decreased from 100 to 2.5 mg/L in 240 min. In both cases, the residual concentration of B was highlighted to be lower than the current Japanese effluent standards (10 mg/L). The removal of B can be explained by way of pseudo-first-order reaction kinetics. The apparent activation energy of 63.5 kJ mol(-1), calculated from the Arrhenius plot indicating that a chemical reaction dominates the removal of B by Mg-Al oxide (Mg/Al = 2). The adsorption of B acts upon a Langmuir-type phenomena. The maximum adsorption (qm) and equilibrium adsorption constants (KL) were 7.4 mmol g(-1) and 1.9 × 10(3), respectively, for Mg-Al oxide (Mg/Al = 2). [Formula: see text] in B(OH)4·Mg-Al LDH produced by the removal of B was observed to undergo anion exchange with [Formula: see text] in solution. Following regeneration, the Mg-Al oxide maintained the ability to remove B from an aqueous solution. This study has clarified the possibility of recycling Mg-Al oxide for B removal. PMID:26454072

  10. ATOMIC AND MOLECULAR PHYSICS: Unique Magnetic Moment and Electronic Properties for Fe(MgO)n(n = 1-8) Clusters: First-Principles Calculations

    NASA Astrophysics Data System (ADS)

    Ge, Gui-Xian; Jing, Qun; Yang, Zeng-Qiang; Luo, You-Hua

    2009-08-01

    The geometries and electronic properties of Fe(MgO)n are systematically investigated by the density functional theory. The results show that the doped Fe atom is prone to bond with the O atom, and Fe almost does not disturb the frame of (MgO)n. The second-order energy difference, the fragmentation energies and the electron affinities show that Fe(MgO)4 and Fe(MgO)6 possess relatively higher stabilities. The HOMO-LUMO gaps of Fe(MgO)n decrease obviously as compared with (MgO)n. Almost equal unpaired electrons of the 3d state of the Fe atom in Fe(MgO)n result in a nearly equal magnetic moment of Fe(MgO)n.

  11. X-ray absorption and magnetic circular dichroism studies of Co2FeAl in magnetic tunnel junctions

    SciTech Connect

    Ebke, D.; Kugler, Z.; Thomas, P.; Schebaum, O.; Schafers, M.; Nissen, D.; Schmalhorst, J.; Hutten, A.; Arenholz, E.; Thomas, A.

    2010-01-11

    The bulk magnetic moment and the element specific magnetic moment of Co{sub 2}FeAl thin films were examined as a function of annealing temperature by alternating gradient magnetometer (AGM) and X-ray absorption spectroscopy (XAS)/X-ray magnetic circular dichroism (XMCD), respectively. A high magnetic moment can be achieved for all annealing temperatures and the predicted bulk and interface magnetic moment of about 5 {tilde A}{sub B} are reached via heating. We will also present tunnel magnetoresistance (TMR) values of up to 153% at room temperature and 260% at 13 K for MgO based magnetic tunnel junctions (MTJs) with Co{sub 2}FeAl and Co-Fe electrodes.

  12. Improved p-type conductivity in Al-rich AlGaN using multidimensional Mg-doped superlattices

    PubMed Central

    Zheng, T. C.; Lin, W.; Liu, R.; Cai, D. J.; Li, J. C.; Li, S. P.; Kang, J. Y.

    2016-01-01

    A novel multidimensional Mg-doped superlattice (SL) is proposed to enhance vertical hole conductivity in conventional Mg-doped AlGaN SL which generally suffers from large potential barrier for holes. Electronic structure calculations within the first-principle theoretical framework indicate that the densities of states (DOS) of the valence band nearby the Fermi level are more delocalized along the c-axis than that in conventional SL, and the potential barrier significantly decreases. Hole concentration is greatly enhanced in the barrier of multidimensional SL. Detailed comparisons of partial charges and decomposed DOS reveal that the improvement of vertical conductance may be ascribed to the stronger pz hybridization between Mg and N. Based on the theoretical analysis, highly conductive p-type multidimensional Al0.63Ga0.37N/Al0.51Ga0.49N SLs are grown with identified steps via metalorganic vapor-phase epitaxy. The hole concentration reaches up to 3.5 × 1018 cm−3, while the corresponding resistivity reduces to 0.7 Ω cm at room temperature, which is tens times improvement in conductivity compared with that of conventional SLs. High hole concentration can be maintained even at 100 K. High p-type conductivity in Al-rich structural material is an important step for the future design of superior AlGaN-based deep ultraviolet devices. PMID:26906334

  13. Tuning Acid-Base Properties Using Mg-Al Oxide Atomic Layer Deposition.

    PubMed

    Jackson, David H K; O'Neill, Brandon J; Lee, Jechan; Huber, George W; Dumesic, James A; Kuech, Thomas F

    2015-08-01

    Atomic layer deposition (ALD) was used to coat γ-Al2O3 particles with oxide films of varying Mg/Al atomic ratios, which resulted in systematic variation of the acid and base site areal densities. Variation of Mg/Al also affected morphological features such as crystalline phase, pore size distribution, and base site proximity. Areal base site density increased with increasing Mg content, while acid site density went through a maximum with a similar number of Mg and Al atoms in the coating. This behavior leads to nonlinearity in the relationship between Mg/Al and acid/base site ratio. The physical and chemical properties were elucidated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2 physisorption, and CO2 and NH3 temperature-programmed desorption (TPD). Fluorescence emission spectroscopy of samples grafted with 1-pyrenebutyric acid (PBA) was used for analysis of base site proximity. The degree of base site clustering was correlated to acid site density. Catalytic activity in the self-condensation of acetone was dependent on sample base site density and independent of acid site density. PMID:26168188

  14. Tuning Acid-Base Properties Using Mg-Al Oxide Atomic Layer Deposition.

    PubMed

    Jackson, David H K; O'Neill, Brandon J; Lee, Jechan; Huber, George W; Dumesic, James A; Kuech, Thomas F

    2015-08-01

    Atomic layer deposition (ALD) was used to coat γ-Al2O3 particles with oxide films of varying Mg/Al atomic ratios, which resulted in systematic variation of the acid and base site areal densities. Variation of Mg/Al also affected morphological features such as crystalline phase, pore size distribution, and base site proximity. Areal base site density increased with increasing Mg content, while acid site density went through a maximum with a similar number of Mg and Al atoms in the coating. This behavior leads to nonlinearity in the relationship between Mg/Al and acid/base site ratio. The physical and chemical properties were elucidated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2 physisorption, and CO2 and NH3 temperature-programmed desorption (TPD). Fluorescence emission spectroscopy of samples grafted with 1-pyrenebutyric acid (PBA) was used for analysis of base site proximity. The degree of base site clustering was correlated to acid site density. Catalytic activity in the self-condensation of acetone was dependent on sample base site density and independent of acid site density.

  15. Improve sensitization and corrosion resistance of an Al-Mg alloy by optimization of grain boundaries.

    PubMed

    Yan, Jianfeng; Heckman, Nathan M; Velasco, Leonardo; Hodge, Andrea M

    2016-01-01

    The sensitization and subsequent intergranular corrosion of Al-5.3 wt.% Mg alloy has been shown to be an important factor in stress corrosion cracking of Al-Mg alloys. Understanding sensitization requires the review of grain boundary character on the precipitation process which can assist in developing and designing alloys with improved corrosion resistance. This study shows that the degree of precipitation in Al-Mg alloy is dependent on grain boundary misorientation angle, adjacent grain boundary planes and grain boundary types. The results show that the misorientation angle is the most important factor influencing precipitation in grain boundaries of the Al-Mg alloy. Low angle grain boundaries (≤15°) have better immunity to precipitation and grain boundary acid attack. High angle grain boundaries (>15°) are vulnerable to grain boundary acid attack. Grain boundaries with adjacent plane orientations near to {100} have potential for immunity to precipitation and grain boundary acid attack. This work shows that low Σ (Σ ≤ 29) coincident site lattice (CSL) grain boundaries have thinner β precipitates. Modified nitric acid mass loss test and polarization test demonstrated that the global corrosion resistance of sputtered Al-Mg alloy is enhanced. This may be attributed to the increased fractions of low Σ (Σ ≤ 29) CSL grain boundaries after sputtering. PMID:27230299

  16. Improve sensitization and corrosion resistance of an Al-Mg alloy by optimization of grain boundaries

    PubMed Central

    Yan, Jianfeng; Heckman, Nathan M.; Velasco, Leonardo; Hodge, Andrea M.

    2016-01-01

    The sensitization and subsequent intergranular corrosion of Al-5.3 wt.% Mg alloy has been shown to be an important factor in stress corrosion cracking of Al-Mg alloys. Understanding sensitization requires the review of grain boundary character on the precipitation process which can assist in developing and designing alloys with improved corrosion resistance. This study shows that the degree of precipitation in Al-Mg alloy is dependent on grain boundary misorientation angle, adjacent grain boundary planes and grain boundary types. The results show that the misorientation angle is the most important factor influencing precipitation in grain boundaries of the Al-Mg alloy. Low angle grain boundaries (≤15°) have better immunity to precipitation and grain boundary acid attack. High angle grain boundaries (>15°) are vulnerable to grain boundary acid attack. Grain boundaries with adjacent plane orientations near to {100} have potential for immunity to precipitation and grain boundary acid attack. This work shows that low Σ (Σ ≤ 29) coincident site lattice (CSL) grain boundaries have thinner β precipitates. Modified nitric acid mass loss test and polarization test demonstrated that the global corrosion resistance of sputtered Al-Mg alloy is enhanced. This may be attributed to the increased fractions of low Σ (Σ ≤ 29) CSL grain boundaries after sputtering. PMID:27230299

  17. Tuneable ultra high specific surface area Mg/Al-CO3 layered double hydroxides.

    PubMed

    Chen, Chunping; Wangriya, Aunchana; Buffet, Jean-Charles; O'Hare, Dermot

    2015-10-01

    We report the synthesis of tuneable ultra high specific surface area Aqueous Miscible Organic solvent-Layered Double Hydroxides (AMO-LDHs). We have investigated the effects of different solvent dispersion volumes, dispersion times and the number of re-dispersion cycles specific surface area of AMO-LDHs. In particular, the effects of acetone dispersion on two different morphology AMO-LDHs (Mg3Al-CO3 AMO-LDH flowers and Mg3Al-CO3 AMO-LDH plates) was investigated. It was found that the amount of acetone used in the dispersion step process can significantly affect the specific surface area of Mg3Al-CO3 AMO-LDH flowers while the dispersion time in acetone is critical factor to obtain high specific surface area Mg3Al-CO3 AMO-LDH plates. Optimisation of the acetone washing steps enables Mg3Al-CO3 AMO-LDH to have high specific surface area up to 365 m(2) g(-1) for LDH flowers and 263 m(2) g(-1) for LDH plates. In addition, spray drying was found to be an effective and practical drying method to increase the specific surface area by a factor of 1.75. Our findings now form the basis of an effective general strategy to obtain ultrahigh specific surface area LDHs.

  18. A new class of ultra-hard materials based on AlMgB{sub 14}

    SciTech Connect

    Cook, B.A.; Harringa, J.L.; Lewis, T.L.; Russell, A.M.

    2000-02-01

    In this study, aluminum magnesium boride combined with 5 to 30 mol.% additives (AlMgB{sub 14}:X where X = Si, P, C, AlN, TiB{sub 2}, or BN), were prepared by mechanical alloying and consolidated by vacuum hot pressing. Matkovich and Economy first reported the orthorhombic AlMgB{sub 14} intermetallic compound (oI64, space group Imam, a - 0.5848 nm, b = 0.8112 nm, c = 1.0312 nm), and the structure determination was later refined by Higashi and Ito. The unit cell is based on four B{sub 12} icosahedral units centered at (0, 0, 0), (0, 0.5, 0.5), (0.5, 0, 0), and (0.5, 0.5, 0.5) within the unit cell. The remaining eight B atoms lie outside the icosahedra, bonding to the icosahedral B atoms and to the Al and Mg atoms. The Al atoms occupy a four-fold position at (0.250, 0.750, 0.250), and the Mg atoms occupy a four-fold position at (0.250, 0.359, 0). The icosahedra are arranged in distorted, close-packed layers. The unique electronic, optical, and mechanical properties of this material are due to a complex icosahedra (intericosahedral bonding). The highest hardness was observed in the AlMgB{sub 14} + 30%TiB{sub 2} material, which possesses a multi-phase microstructure. Here again, an increase in hardness accompanying the introduction of additional phases is somewhat surprising and difficult to explain. The possible compounds that may form at the AlMgB{sub 14}-TiB{sub 2} interface during hot pressing are numerous.

  19. Conduction electron spin resonance in Mg 1 - x Al x B2

    NASA Astrophysics Data System (ADS)

    Likodimos, V.; Koutandos, S.; Pissas, M.; Papavassiliou, G.; Prassides, K.

    2003-01-01

    Conduction electron spin resonance is employed to study the interplay of the electronic and structural properties in the normal state of Mg 1 - x Al x B2 alloys as a function of Al-doping for 0 <= x <= 1. The x-dependence of the spin susceptibility reveals considerable reduction of the total density of states N(EF) with increasing Al concentration, complying with theoretical predictions for a predominant filling effect of the hole σ bands by electron doping. The CESR linewidth exhibits significant broadening, especially prominent in the high-Al-content region, indicative of the presence of enhanced structural disorder, consistent with the presence of compositional fluctuations.

  20. Optical properties of heusler alloys Co2FeSi, Co2FeAl, Co2CrAl, and Co2CrGa

    NASA Astrophysics Data System (ADS)

    Shreder, E. I.; Svyazhin, A. D.; Belozerova, K. A.

    2013-11-01

    The results of an investigation of optical properties and the calculations of the electronic structure of Co2FeSi, Co2FeAl, Co2CrAl, and Co2CrGa Heusler alloys are presented. The main focus of our attention is the study of the spectral dependence of the real part (ɛ1) and imaginary part (ɛ2) of the dielectric constant in the range of wavelengths λ = 0.3-13 μm using the ellipsometric method. An anomalous behavior of the optical conductivity σ(ω) has been found in the infrared range in the Co2CrAl and Co2CrGa alloys, which differs substantially from that in the Co2FeSi and Co2FeAl alloys. The results obtained are discussed based on the calculations of the electronic structure.

  1. Study of Different Al/Mg Powders in Hydroreactive Fuel Propellant Used for Water Ramjet

    NASA Astrophysics Data System (ADS)

    Huang, Hai-Tao; Zou, Mei-Shuai; Guo, Xiao-Yan; Yang, Rong-Jie; Li, Yun-Kai; Jiang, En-Zhou; Li, Zhong-Shan

    2014-05-01

    Experiments were conducted to study the effect of magnesium-aluminum alloy on the combustion performance of hydroreactive fuel propellants. The raw metal powders added to the propellants were ball-milled magnesium-50% aluminum alloy (m-AM), magnesium-50% aluminum alloy (AM), and Al and magnesium (Mg) powders, which were characterized using scanning electron microscopy, X-ray diffraction (XRD), and simultaneous thermogravimetric analysis (TGA). A high-pressure combustor and a metal/steam reactor were used to simulate the two-stage combustion of hydroreactive propellants used for a water ramjet. The combustion performance of the metal powders in propellant was studied experimentally, and the efficiency of the Al reaction in the propellants during the two-stage combustion was calculated. TGA traces in air indicated that the oxidation onset temperature of AM powders is much lower than for both Mg and Al powders. The XRD patterns for the AM and m-AM alloys exhibited Al12Mg17 diffraction peaks. The hydroreactive fuel propellant systems with added m-AM powder exhibited good performance in terms of burning rate, combustion heat, and the Al reaction efficiency, which was better than that for the propellants containing AM, Mg, and Al powders. At the pressure studied (3.0 MPa), the burning rate of the m-AM-containing propellant was found to be 15 mm s-1, and the heat of primary combustion was 6,878.1 kJ kg-1.

  2. Significantly improved dehydrogenation of ball-milled MgH2 doped with CoFe2O4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Shan, Jiawei; Li, Ping; Wan, Qi; Zhai, Fuqiang; Zhang, Jun; Li, Ziliang; Liu, Zhaojiang; Volinsky, Alex A.; Qu, Xuanhui

    2014-12-01

    CoFe2O4 nanoparticles are added to magnesium hydride (MgH2) by high-energy ball milling in order to improve its hydriding properties. The hydrogen storage properties and catalytic mechanism are investigated by pressure-composition-temperature (PCT), differential thermal analysis (DTA), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The nonisothermal desorption results show that the onset desorption temperature of the MgH2 + 7 mol% CoFe2O4 is 160 °C, which is 200 °C lower than of the as-received MgH2. The dehydrogenation process of the MgH2 doped with the CoFe2O4 nanoparticles includes two steps. DTA curves and XRD patterns reveal that a chemical reaction happens between MgH2 and CoFe2O4, forming the final products of the ternary combination, corresponding to Co3Fe7, MgO and Co. The onset desorption temperature of the ball-milled MgH2 doped with Co3Fe7, MgO and Co is about 260 °C, approximately 100 °C lower than the un-doped MgH2, demonstrating that the ternary combination (Co3Fe7, MgO, and Co) also has a great catalytic effect on the MgH2 hydrogen storage properties. It is also confirmed that the various methods of adding the ternary combination have different effects on the MgH2 hydriding-dehydriding process.

  3. Tunable p-type conductivity and transport properties of AlN nanowires via Mg doping.

    PubMed

    Tang, Yong-Bing; Bo, Xiang-Hui; Xu, Jun; Cao, Yu-Lin; Chen, Zhen-Hua; Song, Hai-Sheng; Liu, Chao-Ping; Hung, Tak-Fu; Zhang, Wen-Jun; Cheng, Hui-Ming; Bello, Igor; Lee, Shuit-Tong; Lee, Chun-Sing

    2011-05-24

    Arrays of well-aligned AlN nanowires (NWs) with tunable p-type conductivity were synthesized on Si(111) substrates using bis(cyclopentadienyl)magnesium (Cp(2)Mg) vapor as a doping source by chemical vapor deposition. The Mg-doped AlN NWs are single-crystalline and grow along the [001] direction. Gate-voltage-dependent transport measurements on field-effect transistors constructed from individual NWs revealed the transition from n-type conductivity in the undoped AlN NWs to p-type conductivity in the Mg-doped NWs. By adjusting the doping gas flow rate (0-10 sccm), the conductivity of AlN NWs can be tuned over 7 orders of magnitude from (3.8-8.5) × 10(-6) Ω(-1) cm(-1) for the undoped sample to 15.6-24.4 Ω(-1) cm(-1) for the Mg-doped AlN NWs. Hole concentration as high as 4.7 × 10(19) cm(-3) was achieved for the heaviest doping. In addition, the maximum hole mobility (∼6.4 cm(2)/V s) in p-type AlN NWs is much higher than that of Mg-doped AlN films (∼1.0 cm(2)/V s). (2) The realization of p-type AlN NWs with tunable electrical transport properties may open great potential in developing practical nanodevices such as deep-UV light-emitting diodes and photodetectors. PMID:21480640

  4. Significant improvement of critical current density in MgB2 doped with ferromagnetic Fe3O4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Qu, B.; Sun, X. D.; Li, J.-G.; Xiu, Z. M.; Liu, S. H.; Xue, C. P.

    2009-01-01

    Ferromagnetic Fe3O4-doped MgB2 bulks were first fabricated in this work by the hot pressing method. It was found that Fe3O4 does not react with Mg or B during the fabrication process. Peak Jc values of the 5 wt% Fe3O4-doped MgB2 are higher than 106 A cm-2 in the temperature range 5-30 K. Especially at 30 K, the peak Jc is 1.02 × 106 A cm-2 for the 5 wt% Fe3O4-doped MgB2, the highest values at 30 K found in the literature, and about seven times that of the 5 wt% SiC-doped MgB2 sample. The drop in Jc with increasing field for the Fe3O4-doped MgB2 is significantly slower than that of the SiC-doped MgB2 at 30 K. These results indicate that the Fe3O4-doped MgB2 is a potential superconductor to be used at temperatures greater than 25 K which is a critical temperature for large-scale practical applications.

  5. THE LICK/SDSS LIBRARY. II. [Ca/Fe] AND [Mg/Fe] IN F, G, AND K STARS FROM SDSS-DR7

    SciTech Connect

    Franchini, M.; Morossi, C.; Di Marcantonio, P.; Malagnini, M. L.; Chavez, M. E-mail: morossi@oats.inaf.it E-mail: malagnini@oats.inaf.it

    2011-04-01

    We analyzed the spectra of 17,600 F, G, and K stars extracted from the seventh Sloan Digital Sky Survey Data Release (SDSS-DR7) database in order to derive ([{alpha}/Fe]), [Ca/Fe], and [Mg/Fe] ratios. Particular attention has been devoted to estimating homogeneous and self-consistent atmospheric parameter values, T{sub eff}, log g, and [Fe/H], by comparing synthetic and observational Lick/SDSS indices. We present results for the sub-sample of more than 4000 spectra whose overall quality allowed us to derive fairly accurate stellar atmospheric parameter values and, therefore, reliable abundance ratios. A Monte Carlo approach was adopted to evaluate both the errors in the observational Lick/SDSS indices and in the derived parameter estimates. The analysis of the trends of [Ca/Fe] and [Mg/Fe] versus [Fe/H] pointed out that (1) the [Ca/Fe] and [Mg/Fe] ratios increase with decreasing [Fe/H] with different slopes reaching maximum average levels of +0.25 and +0.40 dex at [Fe/H] {approx_equal} -1.75, respectively; (2) our sample contains, at a given [Fe/H], stars characterized by significantly different amounts of {alpha}-enhancement, thus belonging to different Galactic populations; and (3) the analyzed sample shows a predominance of thick disk stars for [Fe/H] > - 0.5 and the presence of stars belonging to the 'high-{alpha}' halo population for -2.0 < [Fe/H] <-0.5.

  6. Electronic structure studies of chemically synthesized MgFe2O4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Singh, Jitendra Pal; Won, Sung Ok; Lim, Weon Cheol; Lee, Ik-Jae; Chae, K. H.

    2016-03-01

    For present work, magnesium ferrite nanoparticles were synthesized using nitrates of metal ions and citric acid. Crystallite size of these nanoparticles varies from 2.1 ± 0.1 to 62 ± 10 nm as annealing temperatures increases from 300 to 1200 °C. Mg K-edge near-edge X-ray absorption fine-structure spectra reflect the presence of Mg2+ ions in both tetrahedral (A-site) and octahedral (B-site) environment for nanoparticles synthesized at all temperatures. The integral area of spectral features of O K-edge spectra is associated with the change of unoccupied O p-projected density of states. Fe L-edge spectra envisage the presence of Fe3+ state in these nanoparticles. Observed changes in the electronic structure of these nanoparticles are discussed on the basis of cation migration from A-site to B-site, degree of crystallization, and unsaturated bonds at crystallite surface. Fe-O distances at A-site and B-site changes with annealing temperature.

  7. Elastic and Thermodynamic Properties of Complex Mg-Al Intermetallic Compounds via Orbital-Free Density Functional Theory

    NASA Astrophysics Data System (ADS)

    Zhuang, Houlong; Chen, Mohan; Carter, Emily A.

    2016-06-01

    Magnesium-aluminum (Mg-Al) alloys are important metal alloys with a wide range of engineering applications. We investigate the elastic and thermodynamic properties of Mg, Al, and four stoichiometric Mg-Al compounds including Mg17Al12 , Mg13Al14 , and Mg23Al30 , and MgAl2 with orbital-free density-functional theory (OFDFT). We first calculate the lattice constants, zero-temperature formation energy, and independent elastic constants of these six materials and compare the results to those computed via Kohn-Sham DFT (KSDFT) benchmarks. We obtain excellent agreement between these two methods. Our calculated elastic constants of hexagonal close-packed Mg and face-centered-cubic Al are also consistent with available experimental data. We next compute their phonon spectra using the force constants extracted from the very fast OFDFT calculations, because such calculations are computationally challenging using KSDFT. This is especially the case for the Mg23Al30 compound, whose 3 ×3 ×3 supercell consists of 1431 atoms. We finally employ the quasiharmonic approximation to investigate temperature-dependent thermodynamic properties, including formation energies, heat capacities, and thermal expansion of the four Mg-Al intermetallic compounds. The calculated heat capacity and thermal expansion of both Mg and Al agree well with experimental data. We additionally find that Mg13Al14 and MgAl2 are both unstable, consistent with their absence from the equilibrium Mg-Al phase diagram. Our work demonstrates that OFDFT is an efficient and accurate quantum-mechanical computational tool for predicting elastic and thermodynamic properties of complicated Mg-Al alloys and also should be applicable to many other engineering alloys.

  8. Effect of the composition of Al-Li alloys on the quantitative relation between the δ'(Al3Li), S1(Al2MgLi), and T1(Al2CuLi) phases

    NASA Astrophysics Data System (ADS)

    Betsofen, S. Ya.; Antipov, V. V.; Grushin, I. A.; Knyazev, M. I.; Khokhlatova, L. B.; Alekseev, A. A.

    2015-01-01

    Al-Li alloys are considered. A quantitative approach to the determination of the ratio of the fractions of the binary and ternary intermetallic phases in Al-Mg(Cu)-Li alloys is developed on the basis of chemical and phase composition balance equations and the experimentally measured lattice parameter of the α solid solution. The ratio of the fractions of the δ'(Al3Li) and S1(T1) phases in Al-Mg(Cu)-Li alloys is shown to be determined by the ratio of the mole fractions of Li and Mg(Cu). Equations are proposed for calculating the weight fractions of the S1(Al2MgLi), T1(Al2CuLi) and δ'(Al3Li) phases in domestic and foreign Al-Mg-Li alloys 1420, 1424, 5090 and Al-Cu-Li alloys 1440, 1460, 1461, 1441, 1469, 2090, 2095, 8090, and Weldalite 049.

  9. Compression of MgSiO3 and (Mg,Fe)SiO3 perovskites based on the pressure generation technique using sintered diamond anvils in a Kawai-type apparatus

    NASA Astrophysics Data System (ADS)

    Yamazaki, D.; Ito, E.; Yoshino, T.; Shimojuku, A.; Yoneda, A.; Shan, S.; Guo, X.; Higo, Y.; Funakoshi, K.

    2010-12-01

    (Mg,Fe)SiO3 perovskite and ferro-periclase are abundant minerals in the Earth’s lower mantle and hence their pressure-volume-temperature (P-V-T) relations are very useful in interpreting the seismological observations. Previous researches suggested the significant change of compressibility (P-V relation) of ferro-periclase due to the spin transition in iron at pressure of 30-70 GPa (Fei et al., 2008; Ito et al, 2010), whereas compressibility change caused by spin transition in (Mg,Fe)SiO3 perovskite is not reported yet. Iron content in silicate perovskite is much lower than that in ferro-periclase and pressures for spin transition in perovskite is expected to be higher than 70 GPa. Therefore, precise determination of volume at wide pressure range is required to access the change of P-V relation associated with spin transition in perovskite. Although pressure range in Kawai-type multianvil high pressure apparatus (KMA) is insufficient to cover whole mantle conditions, KMA enables us to have a large sample and uniform heating for high temperature experiment. In this study, we developed the experimental technique to expand the pressure range in KMA and applied this technique to measure the volumes of MgSiO3 and (Mg,Fe)SiO3 perovskites to observe the change in P-V curve related to spin transition. We conducted high pressure experiments at synchrotron facility, SPring-8, Japan, using a KMA equipped with sintered diamond anvils with 1.0 mm truncated edge length, and we succeeded to expand the pressure limit to ~ 95 GPa (at press of 6.5 MN) at 700 K based on Au pressure standard (Tsuchiya, 2003). In the experiment, we measured the volumes of MgSiO3 and (Mg,Fe)SiO3 perovskites simultaneously as a function of temperature and pressure. In this pressure range, little change in the volume ratio between MgSiO and (Mg,Fe)SiO3 perovskites is expected by preliminary volume analyses. We re-calculate the volumes and expand pressure range more and more in future.

  10. Hardness and microstructural variation of Al-Mg-Mn-Sc-Zr alloy.

    PubMed

    Ikeshita, Sumiha; Strodahs, Ansis; Saghi, Zineb; Yamada, Kazuhiro; Burdet, Pierre; Hata, Satoshi; Ikeda, Ken-Ichi; Midgley, Paul A; Kaneko, Kenji

    2016-03-01

    Variations of Vickers hardness were observed in Al-Mg-Mn alloy and Al-Mg-Mn-Sc-Zr alloy at different ageing times, ranging from a peak value of 81.2 HV at 54 ks down to 67.4 HV at 360 ks, below the initial hardness value, 71.8 HV at 0 ks for the case of Al-Mg-Mn-Sc-Zr alloy. Microstructures of samples at each ageing stage were examined carefully by transmission electron microscopes (TEMs) both in two-dimensions and three-dimensions. The presence of different types, densities, and sizes of particles were observed dispersed spherical Al3Sc1-xZrx and also block-shaped Al3Sc precipitates growing along <100>Al with facets {100} and {110} of the precipitates. TEM analysis both in two-dimensions and three-dimensions, performed on various samples, confirmed the direct correlation between the hardness and the density of Al3Sc.

  11. Hardness and microstructural variation of Al-Mg-Mn-Sc-Zr alloy.

    PubMed

    Ikeshita, Sumiha; Strodahs, Ansis; Saghi, Zineb; Yamada, Kazuhiro; Burdet, Pierre; Hata, Satoshi; Ikeda, Ken-Ichi; Midgley, Paul A; Kaneko, Kenji

    2016-03-01

    Variations of Vickers hardness were observed in Al-Mg-Mn alloy and Al-Mg-Mn-Sc-Zr alloy at different ageing times, ranging from a peak value of 81.2 HV at 54 ks down to 67.4 HV at 360 ks, below the initial hardness value, 71.8 HV at 0 ks for the case of Al-Mg-Mn-Sc-Zr alloy. Microstructures of samples at each ageing stage were examined carefully by transmission electron microscopes (TEMs) both in two-dimensions and three-dimensions. The presence of different types, densities, and sizes of particles were observed dispersed spherical Al3Sc1-xZrx and also block-shaped Al3Sc precipitates growing along <100>Al with facets {100} and {110} of the precipitates. TEM analysis both in two-dimensions and three-dimensions, performed on various samples, confirmed the direct correlation between the hardness and the density of Al3Sc. PMID:26748212

  12. Removal of perchlorate in water by calcined MgAl-CO3 layered double hydroxides.

    PubMed

    Yang, Yiqiong; Gao, Naiyun; Deng, Yang; Yu, Guoping

    2013-04-01

    Perchlorate is widely known as an inorganic endocrine disruptor. In this study, MgAl-CO3 layered double hydroxides with different Mg/Al molar ratios were prepared using a coprecipitation method and followed by a calcination process at a temperature range of 300 to 700 degrees C. Results showed that the best synthesis conditions were a calcination temperature of 550 degrees C and Mg/Al molar ratio of 3. Further, the adsorbent and its adsorption product were characterized by x-ray diffraction, Fourier transform-infrared spectroscopy, and thermogravimetric-differential thermal analysis. The layered double hydroxides structures in the adsorbent were lost during calcination at 550 degrees C but were reconstructed subsequent to adsorption of perchlorate, indicating that the "memory effect" appeared to play an important role in perchlorate adsorption. The perchlorate adsorption pattern was best described by the pseudo-second-order kinetics model, while the Freundlich isotherms appropriately explained perchlorate adsorption data.

  13. Intruder Configurations in the A=33 Isobars: {sup 33}Mg and {sup 33}Al

    SciTech Connect

    Tripathi, Vandana; Tabor, S. L.; Bender, P.; Hoffman, C. R.; Lee, Sangjin; Perry, M.; Pepper, K.; Volya, A.; Mantica, P. F.; Utsuno, Y.; Cook, J.; Pereira, J.; Weisshaar, D.; Otsuka, T.; Pinter, J. S.; Stoker, J.

    2008-10-03

    The {beta} decay of {sup 33}Mg (N=21) presented in this Letter reveals intruder configurations in both the parent and the daughter nucleus. The lowest excited states in the N=20 daughter nucleus, {sup 33}Al, are found to have nearly 2p-2h intruder configuration, thus extending the 'island of inversion' beyond Mg. The allowed direct {beta}-decay branch to the 5/2{sup +} ground state of the daughter nucleus {sup 33}Al implies positive parity for the ground state of the parent {sup 33}Mg, contrary to an earlier suggestion of negative parity from a g-factor measurement. An admixture of 1p-1h and 3p-3h configurations is proposed for the ground state of {sup 33}Mg to explain all of the experimental observables.

  14. Effect of Ca addition on the corrosion behavior of Mg-Al-Mn alloy

    NASA Astrophysics Data System (ADS)

    Yang, Jiang; Peng, Jian; Nyberg, Eric A.; Pan, Fu-sheng

    2016-04-01

    The microstructures and corrosion resistance of magnesium-5 wt% aluminum-0.3 wt% manganese alloys (Mg-Al-Mn) with different Ca additions (0.2-4 wt%) were investigated. Results showed that with increasing Ca addition, the grain of the alloys became more refined, whereas the corrosion resistant ability of the alloys initially increased and then decreased. The alloy with 2 wt% Ca addition exhibited the best corrosion resistance, attributed to the effect of the oxide film and (Mg,Al)2Ca phases which were discontinuously distributed on the grain boundaries. These phases acted as micro-victims, they preferentially corroded to protect the α-Mg matrix. The oxide film formed on the alloy surface can hinder the solution further to protect the α-Mg matrix.

  15. Irradiation-induced formation of a spinel phase at the FeCr/MgO interface

    SciTech Connect

    Xu, Yun; Yadav, Satyesh Kumar; Aguiar, Jeffery A.; Anderoglu, Osman; Baldwin, Jon Kevin; Wang, Yongqiang; Misra, Amit; Luo, Hongmei; Uberuaga, Blas P.; Li, Nan

    2015-04-27

    Oxide dispersion strengthened ferritic/martensitic alloys have attracted significant attention for their potential uses in future nuclear reactors and storage vessels, as the metal/oxide interfaces act as stable high-strength sinks for point defects while also dispersing helium. Here, in order to unravel the evolution and interplay of interface structure and chemistry upon irradiation in these types of materials, an atomically sharp FeCr/MgO interface was synthesized at 500 °C and separately annealed and irradiated with Ni3+ ions at 500 °C. After annealing, a slight enrichment of Cr atoms was observed at the interface, but no other structural changes were found. However, under irradiation, sufficient Cr diffuses across the interface into the MgO to form a Cr-enriched transition layer that contains spinel precipitates. First-principles calculations indicate that it is energetically favorable to incorporate Cr, but not Fe, substitutionally into MgO. Furthermore, our results indicate that irradiation can be used to form new phases and complexions at interfaces, which may have different radiation tolerance than the pristine structures.

  16. Irradiation-induced formation of a spinel phase at the FeCr/MgO interface

    DOE PAGES

    Xu, Yun; Yadav, Satyesh Kumar; Aguiar, Jeffery A.; Anderoglu, Osman; Baldwin, Jon Kevin; Wang, Yongqiang; Misra, Amit; Luo, Hongmei; Uberuaga, Blas P.; Li, Nan

    2015-04-27

    Oxide dispersion strengthened ferritic/martensitic alloys have attracted significant attention for their potential uses in future nuclear reactors and storage vessels, as the metal/oxide interfaces act as stable high-strength sinks for point defects while also dispersing helium. Here, in order to unravel the evolution and interplay of interface structure and chemistry upon irradiation in these types of materials, an atomically sharp FeCr/MgO interface was synthesized at 500 °C and separately annealed and irradiated with Ni3+ ions at 500 °C. After annealing, a slight enrichment of Cr atoms was observed at the interface, but no other structural changes were found. However, undermore » irradiation, sufficient Cr diffuses across the interface into the MgO to form a Cr-enriched transition layer that contains spinel precipitates. First-principles calculations indicate that it is energetically favorable to incorporate Cr, but not Fe, substitutionally into MgO. Furthermore, our results indicate that irradiation can be used to form new phases and complexions at interfaces, which may have different radiation tolerance than the pristine structures.« less

  17. Structural and magnetic properties of MnPd/Fe grown on MgO(100) substrate: Ab initio studies

    NASA Astrophysics Data System (ADS)

    Malonda-Boungou, B. R.; Magnoungou, J. H. J.; M'Passi-Mabiala, B.; Demangeat, C.

    2016-07-01

    Structural and magnetic properties of ultrathin films MnPd/Fe grown on MgO(001) are investigated using a self-consistent pseudopotential plane waves method based on density functional theory in the Perdew-Burke-Ernzerhof generalized gradient approximation. The results obtained reveal the presence of an antiferromagnetic coupling between successive Mn [100] rows, combined with a ripple where Mn outward atoms exhibit a positive magnetic moment, in the case of Mn overlayer on Fe/MgO(001). In the case of MnPd monolayer ordered alloy, the c(2 × 2) structure formation is more favorable than the p(1 × 2) one, exhibiting a ferromagnetic coupling between Mn neighbor atoms with a positive induced ferromagnetic moment on Pd atoms. Pd atoms are pushed outward. For 1-ML MnxPd1 - x on Fe/MgO, the Mn absolute mean magnetization per atom increases as x coverage increases, whereas the Pd mean induced magnetic moment decreases. For systems alternating Mn and Pd monolayers on Fe/MgO(001), a complex magnetic structure is shown on Mn monolayers: changing from Mn neighboring antiferromagnetic coupling to Mn [010] rows antiferromagnetic behavior. The correlation is made between the electronic structure and the magnetic properties, by comparing filled with partially filled components (Pd, Mn and Fe) d-bands. The magnetization easy-axis changes between the in-plane and the out-of-plane orientations from Fe/MgO to MnPd/Fe/MgO systems.

  18. Characteristics of Pt-K/MgAl2O4 lean NOx trap catalysts

    SciTech Connect

    Kim, Do Heui; Mudiyanselage, Kumudu K.; Szanyi, Janos; Zhu, Haiyang; Kwak, Ja Hun; Peden, Charles HF

    2012-04-30

    We report the various characteristics of Pt-K/MgAl{sub 2}O{sub 4} lean NOx trap (LNT) catalysts including the effect of K loading on nitrate formation/decomposition, NOx storage activity and durability. Upon the adsorption of NO{sub 2} on K/MgAl{sub 2}O{sub 4} samples, potassium nitrates formed on Mg-related sites in MgAl{sub 2}O{sub 4} support are observed, in addition to the typical two potassium nitrates (ionic and bidentate) formed also on Al{sub 2}O{sub 3} supported sample. Based on NO{sub 2} TPD and FTIR results, the Mg-bound KNO{sub 3} thermally decompose at higher temperature than Al-bound KNO{sub 3}, implying its superior thermal stability. At a potassium loading of 5wt%, the temperature of maximum NOx uptake (T{sub max}) is 300 C. Increasing the potassium loading from 5wt% to 10 wt%, the T{sub max} gradually shifted from 300 C to 450 C, indicating the dependence of T{sub max} on the potassium loading. However, increase in potassium loading above 10 wt% only gives rise to the reduction in the overall NOx storage capacity. This work also underlines the obstacles these materials have prior to their practical application (e.g., durability and sulfur poisoning/ removal). This work provides fundamental understanding of Pt-K/MgAl{sub 2}O{sub 4}-based lean NOx trap catalysts, which could be good candidates for high temperature LNT applications.

  19. Study of the structure and properties of laser-welded joints of the Al-Mg-Li alloy

    NASA Astrophysics Data System (ADS)

    Pugacheva, N. B.; Antenorova, N. P.; Senaeva, E. I.

    2015-12-01

    The macro- and microstructures, the distribution of chemical elements and of the values of the microhardness over the width of the zones of remelting and heat-affected zone have been studied after the laser welding of sheets of an Al-Mg-Li alloy. It has been shown that the material of the zone of remelting (1.2 mm thick) represents in itself finely dispersed misoriented dendrites, in the primary branches of which particles of the strengthening δ' phase (Al3Li) with dimensions of no more than 10 nm and in the interdendrite spaces, dispersed particles of the S phase (Al2MgLi and FeAl2) have been revealed. The hardness of the material of the zone of remelting was 108-123 HV 0.05; the hardness of the basic alloy, 150-162 HV 0.05. In the heat-affected zones of thickness 2 mm, the primary recrystallization occurred only in a narrow zone directly at the boundary with the weld. The strength of the welded junction was 470-490 MPa, which corresponds to the regulated degree of strength of the aluminum alloys of this class. The relative elongation of the material of the weld proved to be considerably less than that in the alloy matrix because of the microporosity of the weld material. It is shown that the convective stirring of the melt in the welding pool upon the laser welding made it possible to avoid the appearance of macroscopic defects, but on the microlevel there are observed micropores in the form of spheres with dimensions of 5-50 μm. The solidification of the alloy occurred in such a way that the dendrites had time to grow around the gas bubbles prior to their collapse, forming a sufficiently strong carcass. Inside the dendritic carcass, there have been revealed coarse inclusions (to 200 μm) that consist of oxides (Al2O3, Fe2O3, MgO, SiO2, CaO), of an iron-based alloy, and of the host aluminum alloy.

  20. Thermal equation of state and stability of (Mg0.06Fe0.94)O

    NASA Astrophysics Data System (ADS)

    Wicks, June K.; Jackson, Jennifer M.; Sturhahn, Wolfgang; Zhuravlev, Kirill K.; Tkachev, Sergey N.; Prakapenka, Vitali B.

    2015-12-01

    We present the pressure-volume-temperature (P-V-T) equation of state of polycrystalline (Mg0.06Fe0.94)O (Mw94) determined from laser-heated X-ray diffraction experiments up to 122 GPa and 2100 K, conditions approaching those of the deep mantle. We conducted two sets of experiments, one with an in situ Fe metal oxygen fugacity buffer and one without such a buffer. The internal pressure markers used in these experiments were B 2 -NaCl and hcp-Fe in the buffered experiment and B 2 -NaCl in the unbuffered experiment. In the sampled P-T range of the high temperature part of this study, only the B 1 structure of Mw94 was observed, indicating that the addition of Mg to FeO stabilizes the B 1 phase with respect to the B 8 phase at these conditions. Both datasets were fit to a Birch-Murnaghan and Mie-Grüneisen-Debye thermal equation of state using a new open-source fitting routine, also presented here. Analysis of these data sets using the same internal pressure marker shows that the P-V-T data of Mw94 obtained in the unbuffered experiment are well explained by the equation of state parameters determined from the buffered data set. We have also compared the thermal equation of state of Mw94 to that of wüstite and conclude that Mw94 has measurably distinct thermoelastic properties compared with those of wüstite. We use the results obtained in the buffered experiment to determine the density and bulk sound velocity of Mw94 at the base of the mantle and compare these values to geophysical observations of ultralow-velocity zones.

  1. Testing LaMgAl11O19 crystal for X-ray spectroscopy

    SciTech Connect

    Chen, H; Beiersdorfer, P; Baronova, E; Kalashnikova, I; Stepanenko, M

    2004-03-31

    We investigated the properties of the rare earth crystal LaMgAl{sub 11}O{sub 19} and its application to soft X-ray spectroscopy. Its relative reflectivity and half width rocking curve were measured to up to the reflection order of 28. In addition, a comparative measurement of the iron L-shell soft X-ray line emission was made on the EBIT-I Livermore electron beam ion trap by fielding the LaMgAl{sub 11}O{sub 19} crystal side by side with a rubidium hydrogen phthalate crystal in a flat crystal spectrometer. From these measurements, reflectivity and spectral resolving power were determined.

  2. Production of Ne Auger electrons by Ne/+/ bombardment of Mg and Al surfaces

    NASA Technical Reports Server (NTRS)

    Ferrante, J.; Pepper, S. V.

    1976-01-01

    A description is given of experiments which provide evidence for the production of an inner shell vacancy in the Ne by the asymmetric Ne-Mg and Ne-Al collision. In addition, autoionization states of neutral Ne have been observed. These states are to be distinguished from the more usual case in Auger electron spectroscopy of de-excitation of an ion with a core vacancy. The experiments involved the bombardment of Mg and Al surfaces with Ne(+) ions. A LEED-Auger system equipped with an ion gun and a four-grid retarding potential analyzer operated in the usual dN(E)/dE mode was used.

  3. P- T- X controls on Ca and Na distribution between Mg-Al tourmaline and fluid

    NASA Astrophysics Data System (ADS)

    Berryman, Eleanor J.; Wunder, Bernd; Rhede, Dieter; Schettler, Georg; Franz, Gerhard; Heinrich, Wilhelm

    2016-04-01

    Ca-Na partitioning between tourmaline and a coexisting fluid is investigated in the system CaO-Na2O-B2O3-Al2O3-MgO-SiO2-H2O-Cl between 0.2-4.0 GPa and 500-700 °C. The synthesis experiments produced a mineral assemblage of tourmaline, coesite/quartz, and in some cases additional phases, typically comprising <1 wt% of the solid product. The synthesized tourmalines are solid solutions of dravite [NaMg3Al6Si6O18(BO3)3(OH)3(OH)], "oxy-uvite" (i.e. "Ca-Mg-O root name") [CaMg3Al6Si6O18(BO3)3(OH)3O], and magnesio-foitite [☐(Mg2Al)Al6Si6O18(BO3)3(OH)3(OH)]. Starting materials comprised a fluid of constant ionic strength (2.00 m) and an oxide mixture with a constant Mg/Al ratio. As a result, the number of vacancies at the X site and the Mg/Al ratio of tourmaline crystals synthesized at the same temperature vary only slightly. The major solid solution is Ca-Na exchange at the X site via the exchange vector X Ca W O[ X Na W (OH)]-1, with the exchange vector X (Ca☐)[ X Na2]-1 serving as a secondary Ca-incorporation mechanism. Tourmaline's X-site composition reflects the fluid composition, whereby the Ca (or Na) concentration in the fluid corresponds with the Ca (or Na) content in tourmaline at each pressure and temperature. At 0.2 GPa, 700 °C, Ca preferentially partitions into tourmaline, producing the most Ca-rich tourmaline crystals synthesized here. At pressures >1.0 GPa, Ca partitions preferentially into the fluid, resulting in Na-dominant tourmaline compositions. Temperature has a secondary effect on Ca-Na partitioning, with higher temperatures correlating with increased Ca incorporation in tourmaline. Based on the experimental findings, tourmaline is expected to have Ca-rich compositions when it forms in low pressure, high-temperature Ca-rich rocks, consistent with the current record of tourmaline occurrence. The bulk Mg/Al ratio and the pH of the tourmaline-forming system may also affect Ca incorporation in tourmaline, but remain to be investigated experimentally.

  4. Melting and thermodynamic properties of pyrope (Mg3Al2Si3O12)

    USGS Publications Warehouse

    Tequi, C.; Robie, R.A.; Hemingway, B.S.; Neuville, D.R.; Richet, P.

    1991-01-01

    The heat capacity of Mg3Al2Si3O12 glass has been measured from 10 to 1000 K by adiabatic and differential scanning calorimetry. The heat capacity of crystalline pyrope has been determined from drop-calorimetry measurements between 820 and 1300 K. From these and previously published results a consistent set of thermodynamic data is presented for pyrope and Mg3Al2Si3O12 glass and liquid for the interval 0-2000 K. The enthalpy of fusion at 1570 ?? 30 K, the metastable congruent 1-bar melting point, is 241 ?? 12 kJ/mol. ?? 1991.

  5. Pressure-induced structural phase transition in AlN:Mg and AlN:Co nanowires

    NASA Astrophysics Data System (ADS)

    Xu, Yongsheng; Zhu, Hongyang; Ma, Chunli; Zhu, Pinwen; Cong, Ridong; Wu, Xiaoxin; Gao, Wei; Cui, Qiliang

    2013-06-01

    High-pressure behaviors of AlN:Mg and AlN:Co nanowires have been investigated by in situ angle dispersive synchrotron X-ray diffraction up to 41.5 GPa and 38.2 GPa, respectively. Their corresponding pressure-induced wurtzite-to-rocksalt phase transitions start at 17.7 GPa and 15.0 GPa and complete at 33.2 GPa and 31.0 GPa, respectively. The phase-transition routes are not affected by the doped ions, while the phase transition pressures are lower than that of pure AlN nanowires. The distinct high-pressure behaviors are ascribed to the doped ions, which reduce the formation energy of cation vacancies and induce Al vacancies defects together with substitution defects, resulting in lattice distortion and affecting structural stability and phase transition pressure.

  6. In situ corrosion analysis of Al-Zn-In-Mg-Ti-Ce sacrificial anode alloy

    SciTech Connect

    Ma Jingling Wen Jiuba; Zhai Wenxia; Li Quanan

    2012-03-15

    The corrosion behaviour of Al-5Zn-0.02In-1Mg-0.05Ti-0.5Ce (wt.%) alloy has been investigated by immersion test, scanning electron microscopy, energy dispersive X-ray detector, electrochemical impedance spectroscopy and electrochemical noise. The results show that there exist different corrosion types of the alloy in 3.5% NaCl solution with the immersion time. At the initial stage of immersion, pitting due to the precipitates predominates the corrosion with a typical inductive loop at low frequencies in electrochemical impedance spectroscopy. The major precipitates of the alloy are MgZn{sub 2} and Al{sub 2}CeZn{sub 2} particles. The corrosion potentials of the bulk MgZn{sub 2} and Al{sub 2}CeZn{sub 2} alloys are negative with respect to that of {alpha}-Al, so the MgZn{sub 2} and Al{sub 2}CeZn{sub 2} precipitates can act as activation centre and cause the pitting. In the late corrosion, a relative uniform corrosion predominates the corrosion process controlled by the dissolution/precipitation of the In ions and characterized by a capacitive loop at medium-high frequencies in electrochemical impedance spectroscopy. The potential noise of the pitting shows larger amplitude fluctuation and lower frequency, but the potential noise of the uniform corrosion occurs with smaller amplitude fluctuation and higher frequency.

  7. Enhanced spin signal in nonlocal devices based on a ferromagnetic CoFeAl alloy

    NASA Astrophysics Data System (ADS)

    Bridoux, G.; Costache, M. V.; Van de Vondel, J.; Neumann, I.; Valenzuela, S. O.

    2011-09-01

    We systematically study the nonlocal spin signal in lateral spin valves based on CoFeAl injectors and detectors and compare the results with identically fabricated devices based on CoFe. The devices are fabricated by electron beam evaporation at room temperature. We observe a > 10-fold enhancement of the spin signal in the CoFeAl devices. We explain this increase as due to the formation of a highly spin-polarized Co2FeAl Heusler compound with large resistivity. These results suggest that Heusler compounds are promising candidates as spin polarized electrodes in lateral spin devices for future spintronic applications.

  8. Preparation of Al-Cr-Fe Coatings by Heat Treatment of Electrodeposited Cr/Al Composite Coatings

    NASA Astrophysics Data System (ADS)

    Zhang, Min; Chen, Chang'an; Zhang, Guikai; Rao, Yongchu; Ling, Guoping

    Al-Cr-Fe coatings have been widely used in the surface engineering field of materials, due to their excellent corrosion resistance to water vapor and fused salt deposits. In this study, a new two-step approach was developed to prepare Al-Cr-Fe coatings on surfaces of SUS430 stainless steels. First, the Cr/Al composite coatings were prepared by electrodepositing Cr from aqueous solution then electrodepositing Al from AlCl3-1-ethyl-3-methyl-imidazolium chloride (AlCl3-EMIC) ionic liquid on SUS430 stainless steel substrate. In the second, heat treatment of the Cr/Al composite coatings was carried out to acquire Al-Cr-Fe coatings. Effects of the thickness of Cr/Al composite coatings, the time and temperature of heat treatment on composition and phase structure of alloy layers were studied by using scanning electron microscope (SEM), backscattered electron (BSE), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The structure transformation process and formation mechanism of Al-Cr-Fe coatings were discussed.

  9. Atmospheric reactive plasma sprayed Fe-Al 2 O 3 -FeAl 2 O 4 composite coating and its property evaluation

    NASA Astrophysics Data System (ADS)

    Zhu, Lin; He, Jining; Yan, Dianran; Dong, Yanchun; Zhang, Jianxin; Li, Xiangzhi; Liao, Hanlin

    2011-09-01

    In the present study, Fe-Al2O3-FeAl2O4 composite coatings were successfully deposited by reactive plasma sprayed Al/Fe2O3 agglomerated powder. Phase composition and microstructure of the coatings were determined by XRD and SEM. The results indicated that the composite coatings were principally composed of three different phases, i.e. FeAl2O4 phase as main framework, dispersed ball-like Fe-rich phase, and small splats of Al2O3 phase, and it was thought that the in situ synthesized metal phase was helpful to toughen the coating matrix. According to the results of the indentation and frictional wear tests, the composite coating exhibited excellent toughness and anti-friction properties in comparison with conventional Al2O3 monophase coating, though its microhardness value was a little lower than that of Al2O3 coating. The formation mechanism and the toughening mechanism of the composite coating were clarified in detail.

  10. Molybdenum nitrogenase of Azotobacter chroococcum. Tight binding of MgADP to the MoFe protein.

    PubMed

    Miller, R W; Eady, R R

    1989-11-01

    The dye-oxidized or dithionite-reduced forms of the MoFe protein of molybdenum nitrogenase of Azotobacter chroococcum were shown to bind 2 mol of MgADP/mol of protein, as determined by column equilibrium techniques. The gel-filtration elution profile of unbound Mg[14C]ADP was not symmetrical, consistent with a low rate of dissociation from the protein. Symmetrical elution profiles were observed for the oxidized Fe protein of nitrogenase, which bound 2 mol of MgADP/mol of protein. The low rate of dissociation of MgADP from MoFe protein was shown by non-equilibrium column techniques, where 1 mol of MgADP/mol of MoFe protein remained tightly bound during chromatography. Very weak binding of MgATP (less than 0.01 mol of MgATP/mol of MoFe protein) to dye-oxidized but not to dithionite-reduced MoFe protein was observed. These results are discussed in terms of their relevance to the catalytic cycle of nitrogenase catalysis.

  11. Interactions at the Al-S-Fe interface: S inhibition of aluminum oxidation

    SciTech Connect

    Addepalli, S.G.; Lin, J.S.; Ekstrom, B.; Kelber, J.A.

    1999-08-01

    The deposition of aluminum on S/Fe(111) (1 x 1) at 300 K in UHV results in the formation of a disordered S-modified Al adlayer. Insertion of Al between the sulfur atoms and the Fe substrate is indicated by an increase of the S Auger signal with increasing Al deposition. Room-temperature oxidation of AlS/Fe(111) in UHV is inhibited compared to the oxidation of aluminum deposited on the sulfur-free Fe(111). The oxygen-uptake curves and variations in the S(LVV), Fe(MVV) intensities with oxygen exposure are also consistent with the insertion of the aluminum atoms between the S overlayer and the Fe substrate.

  12. Consolidation processing parameters and alternative processing methods for powder metallurgy Al-Cu-Mg-X-X alloys

    NASA Technical Reports Server (NTRS)

    Sankaran, K. K.

    1987-01-01

    The effects of varying the vacuum degassing parameters on the microstructure and properties of Al-4Cu-1Mg-X-X (X-X = 1.5Li-0.2Zr or 1.5Fe-0.75Ce) alloys processed from either prealloyed (PA) or mechanically alloyed (M) powder, and consolidated by either using sealed aluminum containers or containerless vacuum hot pressing were studied. The consolidated billets were hot extruded to evaluate microstructure and properties. The MA Li-containing alloy did not include Zr, and the MA Fe- and Ce-containing alloy was made from both elemental and partially prealloyed powder. The alloys were vacuum degassed both above and below the solution heat treatment temperature. While vacuum degassing lowered the hydrogen content of these alloys, the range over which the vacuum degassing parameters were varied was not large enough to cause significant changes in degassing efficiency, and the observed variations in the mechanical properties of the heat treated alloys were attributed to varying contributions to strengthening by the sub-structure and the dispersoids. Mechanical alloying increased the strength over that of alloys of similar composition made from PA powder. The inferior properties in the transverse orientation, especially in the Li-containing alloys, suggested deficiencies in degassing. Among all of the alloys processed for this study, the Fe- and Ce-containing alloys made from MA powder possessed better combinations of strength and toughness.