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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.

    2016-04-01

    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. 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.

  4. Spark plasma sintering of a nanocrystalline Al-Cu-Mg-Fe-Ni-Sc alloy

    NASA Astrophysics Data System (ADS)

    Zúñiga, Alejandro; Ajdelsztajn, Leonardo; Lavernia, Enrique J.

    2006-04-01

    The microstructure and aging behavior of a nanocrystalline Al-Cu-Mg-Fe-Ni-Sc alloy was studied. The nanocrystalline powders were produced by milling at liquid nitrogen temperature and then consolidated using spark plasma sintering (SPS). The microstructure after SPS consisted of a bimodal aluminum grain structure (coarse-grained and fine-grained regions), along with Al9FeNi and Al2CuMg particles dispersed throughout. The microstructure observed in the as-consolidated sample is rationalized on the basis of high current densities that are generated during sintering. Solution treatment and aging of the SPS Al-Cu-Mg-Fe-Ni-Sc sample resulted in softening instead of hardening. This observation can be explained by the reduced amount of Cu, Mg, and Si in solid solution available to form S' Al2CuMg due to the precipitation of Al7FeCu2 and Si-rich particles, and by the fact that rodlike S' Al2CuMg particles could only precipitate out in the coarse-grained regions, greatly decreasing their influence on the hardness. This lack of precipitation in the fine-grained region is argued to represent a new physical observation and is rationalized on the basis of physical and thermodynamic effects. The nanocrystalline SPS Al-Cu-Mg-Fe-Ni-Sc sample was also extremely thermally stable, retaining a fine-grained structure even after solution treatment at 530°C for 5 h. The observed thermal stability is rationalized on the basis of solute drag and Zener pinning caused by the impurities introduced during the cryomilling process.

  5. 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.

  6. Perpendicular magnetic anisotropy in Ta|Co40Fe40B20|MgAl2O4 structures and perpendicular CoFeB|MgAl2O4|CoFeB magnetic tunnel junction

    NASA Astrophysics Data System (ADS)

    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.

    2014-09-01

    Magnetic properties of Co40Fe40B20 (CoFeB) thin films sandwiched between Ta and MgAl2O4 layers have been systematically studied. For as-grown state, Ta/CoFeB/MgAl2O4 structures exhibit good perpendicular magnetic anisotropy (PMA) with interface anisotropy Ki = 1.22 erg/cm2, which further increases to 1.30 erg/cm2 after annealing, while MgAl2O4/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/MgAl2O4/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.

  7. Adsorption of perchlorate from aqueous solution by the calcination product of Mg/(Al-Fe) hydrotalcite-like compounds.

    PubMed

    Yang, Yiqiong; Gao, Naiyun; Chu, Wenhai; Zhang, Yongji; Ma, Yan

    2012-03-30

    The calcination products containing Mg(II), Al(III), and Fe(III) in the brucite-like layers with varying Mg/Al/Fe molar ratios at 550°C were used as the adsorbent to remove perchlorate from aqueous solution, while the Mg/(Al-Fe) hydrotalcite compounds were synthesized by co-precipitation method at a constant pH value. The Mg/(Al-Fe) hydrotalcite compounds (HMAF) were characterized by XRD, FT-IR and TG-DTA. The characteristics showed that the layered double hydroxides structures in the HMAF were lost during calcination at 550°C, but were reconstructed subsequent to adsorption of perchlorate, indicating that the 'memory effect' appeared to play an important role in perchlorate adsorption. Batch adsorption studies were conducted under various equilibration conditions, such as molar ratios of Mg/Al/Fe, calcined temperature, different initial solution pH, adsorbent dose, initial perchlorate concentration, and co-existing anions. It was found that the existence of ferric iron in calcined Mg/(Al-Fe) hydrotalcite compound (CHMAF) was favorable to removal of perchlorate from water, and the best ratio of Mg/Al/Fe is 3:0.8:0.2 (CHMAF5%). This study demonstrated that the calcination product of Mg/(Al-Fe) hydrotalcite-like compound was a promising adsorbent for control of the perchlorate pollution in water. PMID:22325635

  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

    NASA Astrophysics Data System (ADS)

    del Arco, M.; Fernández, A.; Martín, C.; Rives, V.

    2010-12-01

    Following different preparation routes, fenbufen has been intercalated in the interlayer space of layered double hydroxides with Mg 2+ and Al 3+ or Mg 2+, Al 3+ and Fe 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 Å. 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.

  9. 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.

  10. 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.

    2016-06-01

    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.

  11. 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.

  12. 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

  13. Elasticity of spinels in the system (Mg,Fe2+)Al2O4: The effect of Fe-Mg substitution up to 10 GPa

    NASA Astrophysics Data System (ADS)

    Bruschini, E.; Speziale, S.; Andreozzi, G.; Bosi, F.

    2013-12-01

    According to the pyrolite compositional model, spinel-structured compounds are among the most abundant materials of the Earth's mantle (especially in the transition zone between 410 and 660 km depth). It is widely known that iron is the most abundant transition metal in the minerals of the mantle. However, the exact iron content and its heterogeneity in the mantle is still a matter of debate. Fe concentration plays a crucial role in determining a wide range of physical properties of the main minerals of the mantle, In particular it was recently pointed out that heterogeneity of Fe content controls the shear waves velocity much more than temperature variations. We performed Brillouin-scattering measurements at ambient conditions and at high pressure up to 10 GPa of a set of synthetic oxide spinels in the system MgAl2O4 (Spinel s.s.) - FeAl2O4 (Hercynite) in order to assess how the Fe2+ → Mg substitution affects the elastic properties of spinel-structured oxides at high pressure. Our results reveal a strong deviation from linearity of the elastic tensor components (Cij's) as a function of divalent iron content already at low Fe2+ region. With increasing Fe content C11 and C44 show an initial increase followed by a decrease at Fe/(Fe+Mg) > 0.1-0.2 (which is comparable with Fe content in the mantle ringwoodite). With our results we have placed, for the first time, quantitative constraints on the effect of Fe-Mg substitution on the elastic properties of spinel-hercynite solid solutions. Given that the iron content strongly affects the elastic properties of spinel-structured oxides, our results raise the important question of which is the role of both the chemical variability and the cations distribution, especially in terms of FeMg substitution, on the elastic properties of the spinel-structured transition zone silicates (i.e. ringwoodite and wadsleyite). This question needs to be addressed in order to put constrains on the interpretation of seismic features (in

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. Effects of metallurgical parameters on the decomposition of pi-AlFeMgSi phase in Al-Si-Mg alloys and its influence on the mechanical properties

    NASA Astrophysics Data System (ADS)

    Elsharkawi, Ehab A.

    2011-12-01

    The formation of the pi-AlFeMgSi iron intermetallic phase in Al-Si-Mg alloys is known for its detrimental effect on ductility and strength, in that it is controlled by the Fe and Mg content of the alloy, as well as by the cooling rate. The current study was carried out with a view to investigating all the metallurgical parameters affecting the formation of the pi-phase iron intermetallic and, in turn, the role of the pi-phase as it relates to the tensile and impact properties of Al-Si-Mg alloys. Microstructural assessment was carried out by means of quantitative metallography using electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). The results indicate that increasing the Mg and Fe content increases the amount of the pi-AlMgFeSi phase formed. All the alloys containing low levels of iron regardless of the amount of Mg-content show low amounts of pi-phase iron intermetallic. The addition of trace amounts of Be has an observable effect in reducing the amount of the pi-phase formed in all the alloys studied. The pi-phase iron intermetallic particles appear to be segregated away from the modified Si in the Sr-modified alloys, particularly those solidified at a low cooling rate. The effects of different solution treatment times on the decomposition of the pi-phase were investigated in order to examine how this type of decomposition affected the chemistry of the matrix itself. After 8 hours of solution heat treatment and at Mg content of 0.4wt%, the pi-phase showed complete decomposition into fine beta-phase needles. The a-phase, however, showed only partial decomposition into beta-AlFeSi phase needles at Mg levels of over 0.4%wt. This type of decomposition was examined for the purposes of this study over extended periods of solution heat treatment time in Al-7Si-0.55Mg-0.1Fe alloy samples obtained at different cooling rates in order to evaluate the mechanism of pi to beta-phase decomposition. The results obtained show that the volume fraction of

  20. Magnetic Phase Formation in Self-Assembled Epitaxial BiFeO3-MgO and BiFeO3-MgAl2O4 Nanocomposite Films Grown by Combinatorial Pulsed Laser Deposition.

    PubMed

    Kim, Dong Hun; Sun, XueYin; Kim, Tae Cheol; Eun, Yun Jae; Lee, Taeho; Jeong, Sung Gyun; Ross, Caroline A

    2016-02-01

    Self-assembled epitaxial BiFeO3-MgO and BiFeO3-MgAl2O4 nanocomposite thin films were grown on SrTiO3 substrates by pulsed laser deposition. A two-phase columnar structure was observed for BiFeO3-MgO codeposition within a small window of growth parameters, in which the pillars consisted of a magnetic spinel phase (Mg,Fe)3O4 within a BiFeO3 matrix, similar to the growth of BiFeO3-MgFe2O4 nanocomposites reported elsewhere. Further, growth of a nanocomposite with BiFeO3-(CoFe2O4/MgO/MgFe2O4), in which the minority phase was grown from three different targets, gave spinel pillars with a uniform (Mg,Fe,Co)3O4 composition due to interdiffusion during growth, with a bifurcated shape from the merger of neighboring pillars. BiFeO3-MgAl2O4 did not form a well-defined vertical nanocomposite in spite of having lower lattice mismatch, but instead formed a two-phase film with in which the spinel phase contained Fe. These results illustrate the redistribution of Fe between the oxide phases during oxide codeposition to form a ferrimagnetic phase from antiferromagnetic or nonmagnetic targets. PMID:26750565

  1. 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

  2. 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

  3. 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

  4. Modified embedded atom method potential for Al, Si, Mg, Cu, and Fe alloys

    NASA Astrophysics Data System (ADS)

    Jelinek, B.; Groh, S.; Horstemeyer, M. F.; Houze, J.; Kim, S. G.; Wagner, G. J.; Moitra, A.; Baskes, M. I.

    2012-06-01

    A set of modified embedded-atom method (MEAM) potentials for the interactions between Al, Si, Mg, Cu, and Fe was developed from a combination of each element's MEAM potential in order to study metal alloying. Previously published MEAM parameters of single elements have been improved for better agreement to the generalized stacking fault energy (GSFE) curves when compared with ab initio generated GSFE curves. The MEAM parameters for element pairs were constructed based on the structural and elastic properties of element pairs in the NaCl reference structure garnered from ab initio calculations, with adjustment to reproduce the ab initio heat of formation of the most stable binary compounds. The new MEAM potentials were validated by comparing the formation energies of defects, equilibrium volumes, elastic moduli, and heat of formation for several binary compounds with ab initio simulations and experiments. Single elements in their ground-state crystal structure were subjected to heating to test the potentials at elevated temperatures. An Al potential was modified to avoid formation of an unphysical solid structure at high temperatures. The thermal expansion coefficient of a compound with the composition of AA 6061 alloy was evaluated and compared with experimental values. MEAM potential tests performed in this work, utilizing the universal atomistic simulation environment (ASE), are distributed to facilitate reproducibility of the results.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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. PMID:24094226

  15. 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.

  16. 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.

  17. 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.

  18. The Perovskite to Post-Perovskite Transition: Atomistic Simulations of Compositions on the MgSiO3-FeSiO3 and MgSiO3-FeAlO3 Joins

    NASA Astrophysics Data System (ADS)

    Mohn, C.; Tronnes, R. G.

    2014-12-01

    Different atomic arrangements of perovskite (pv) and post-perovskite (ppv) in the systems MgSiO3-FeSiO3 and MgSiO3-FeAlO3 (MS-FS and MS-FA) were examined by Boltzmann statistics and density functional theory (GGA+U). The vibrational contribution to the free energy is calculated within the quasi-harmonic approximation. The FS and FA components partition in opposite directions, towards ppv and pv, respectively. The diverse experimental results on the Fe-partitioning between the two phases are broadly consistent with our theoretical investigation. We determined a Clapeyron slope for the pv-ppv transition of 9.6 MPa/K for MS, decreasing to 8.4 and 8.1 MPa/K at 6.3 and 12.5 mol% FS and to 8.2 and 7.3 MPa/K at 6.3 and 12.5 mol% FA. An isochemical pv to ppv transition within the investigated solid solution range (up tp 25 mol% FS and FA) is characterized by decreasing bulk and increasing shear modulus. At a reference pressure of ­­­100 GPa, the bulk modulus for pv and ppv increases by 1.4% and 1.0%, respectively, from MS to MS-FS12.5 and decreases by 0.4% and 0.2%, respectively, from MS to MS-FA12.5 (subscripts indicate mol%). The shear modulus decreases for both pv and ppv along both of the solid solution series from the pure MS composition, with the largest decrese along the FA-join. For pv and ppv the shear modulus decreases with 2.4% and 1.3%, respectively from MS100 to MS-FS12.5 and with 4.4% and 3.0%, respectively, from MS100 to MS-FA12.5. The results for the MS-FS join are in general agreement with previous DFT-studies (Caracas & Cohen, 2005, GRL; Stackhouse et al. 2006, GRL; Stackhouse & Brodholt 2008, PEPI). Boffa Ballaran et al. (2012, EPSL), however, found a decrease in the bulk modulus for pv on the MS-FS join relative to pure MS. The decreasing bulk modulus along the MS-FA join agrees with Boffa Ballaran et al.A chemical reaction from FA-rich pv and reduced Fe to form FS-rich ppv produces additional Al2O3 and MgO:2 FeAlO3 + 3 MgSiO3 + Fe = 3 FeSiO3 + Al2O3

  19. 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″.

  20. 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).

  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. 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.

  3. 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.

  4. 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.

  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. PMID:26073520

  6. 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.

  7. 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.

  8. Effects of Fe2+ and Zn2+ substitution on the structure and high-pressure stability of MgAl2O4 spinel from DFT calculations

    NASA Astrophysics Data System (ADS)

    Dutta, Rajkrishna; Mandal, Nibir

    2012-09-01

    Using density functional theory we show the effects of transition (Fe2+) and non-transition (Zn2+) divalent cationic substitutions on the following structural parameters: lattice parameters, bond lengths and polyhedral volumes under varying hydrostatic pressures. Fe2+ and Zn2+ substitutions lead to contrasting modifications of tetrahedral Mg-O bond lengths. Fe2+ (50%)increase the tetrahedral Mg-O bond lengths by 0.21%, whereas Zn2+ (50%) reduce it by 0.06%.We present the equations of state of Mg spinel with 50% Fe and Zn substitutions as a function of pressure. This study presents the decomposition pressure (PT) of spinel to periclase (MgO) and corundum (α-Al2O3) as a function of Fe and Zn concentrations (x). For pure spinel, PT=12.1 GPa. Fe2+substitution lowers PT linearly with its concentration as PT=-12.56x+12.02. But, Zn2+ increases PT non-linearly along a quadratic relation: PT=42.057x2+14.171x+12.174. We calculated the C44 elastic constant to explain the contrasting effects of Fe and Zn on the decomposition pressure of spinel phase.

  9. 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.

  10. 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.

  11. 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.

  12. Origin of anomalous magnetite properties in crystallographic matched heterostructures: Fe3O4(111)/MgAl2O4(111).

    PubMed

    Gilks, D; Lari, L; Naughton, J; Cespedes, O; Cai, Z; Gerber, A; Thompson, S M; Ziemer, K; Lazarov, V K

    2013-12-01

    Magnetite films grown on crystallographically matched substrates such as MgAl2O4 are not expected to show anomalous properties such as negative magnetoresistance and high saturation fields. By atomic resolution imaging using scanning transmission electron microscopy we show direct evidence of anti-phase domain boundaries (APB) present in these heterostructures. Experimentally identified 1/4<101> shifts determine the atomic structure of the observed APBs. The dominant non-bulk superexchange interactions are between 180° octahedral-Fe/O/octahedral-Fe sites which provide strong antiferromagnetic coupling across the defect interface resulting in non-bulk magnetic and magnetotransport properties. PMID:24177186

  13. The effect of Sr and Fe additions on the microstructure and mechanical properties of a direct squeeze cast Al-7Si-0.3Mg alloy

    SciTech Connect

    Dong, J.X.; Karnezis, P.A.; Durrant, G.; Cantor, B.

    1999-05-01

    This article describes the results of an investigation into the microstructure and mechanical properties of a gravity die cast and direct squeeze cast LM25 alloy (Al-7Si-0.3Mg-0.3Fe). The direct squeeze cast LM25 alloy has superior mechanical properties compared to the gravity die cast LM25 alloy, especially with regard to ductility, which is increased from {approximately}1.7 pct for the gravity die cast LM25 alloy to {approximately}8.0 pct for the direct squeeze cast LM25 alloy in the T6 heat-treated conditions. This increase in ductility is due to (1) the removal of porosity, (2) a decrease in Si particle size, and (3) a refinement of the Fe-Si-aluminide particles. High cooling rates in direct squeeze casting result in quench modification of the Si particles, such that chemical modification with Sr or Na may not be required. In addition, direct squeeze casting is more tolerant of Fe impurities in the alloy, due to the formation of smaller Fe-Si-aluminide particles than those in gravity die cast material. The direct squeeze cast LM25 + Fe alloy (Al-7Si-0.3Mg-1.0Fe) has a ductility of {approximately}6.5 pct, compared to that of {approximately}0.5 pct for the gravity die cast LM25 + Fe alloy in the T6 heat-treated condition. This increase in tolerance to Fe impurities can lead to a substantial reduction in manufacturing costs due to (1) reduced raw-material costs, (2) reduced die sticking, and (3) improved die life.

  14. The effect of Sr and Fe additions on the microstructure and mechanical properties of a direct squeeze cast Al-7Si-0.3Mg alloy

    NASA Astrophysics Data System (ADS)

    Dong, J. X.; Karnezis, P. A.; Durrant, G.; Cantor, B.

    1999-05-01

    This article describes the results of an investigation into the microstructure and mechanical properties of a gravity die cast and direct squeeze cast LM25 alloy (Al-7Si-0.3Mg-0.3Fe). The direct squeeze cast LM25 alloy has superior mechanical properties compared to the gravity die cast LM25 alloy, especially with regard to ductility, which is increased from ˜1.7 pct for the gravity die cast LM25 alloy to ˜8.0 pct for the direct squeeze cast LM25 alloy in the T6 heat-treated condition. This increase in ductility is due to (1) the removal of porosity, (2) a decrease in Si particle size, and (3) a refinement of the Fe-Si-aluminide particles. High cooling rates in direct squeeze casting result in quench modification of the Si particles, such that chemical modification with Sr or Na may not be required. In addition, direct squeeze casting is more tolerant of Fe impurities in the alloy, due to the formation of smaller Fe-Si-aluminide particles than those in gravity die cast material. The direct squeeze cast LM25+Fe alloy (Al-7Si-0.3Mg-1.0Fe) has a ductility of ˜6.5 pct, compared to that of ˜0.5 pct for the gravity die cast LM25 + Fe alloy in the T6 heat-treated condition. This increase in tolerance to Fe impurities can lead to a substantial reduction in manufacturing costs due to (1) reduced raw-material costs, (2) reduced die sticking, and (3) improved die life.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  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. Effect of Mg on the Corrosion Behaviour of As-Cast and Heat Treated Al-4.5Cu-3.4Fe In-Situ Composites

    NASA Astrophysics Data System (ADS)

    Hossain, Md Delower; Kabir, Mohammad Sharear; Kurny, A. S. W.

    2015-10-01

    The influence of Mg addition on the corrosion behaviour of as-cast and heat treated Al-4.5Cu-3.4Fe in-situ composite was investigated. The composite was produced by solidification processing whereby Al3Fe intermetallic formed in-situ in Al-Cu matrix. Magnesium additions were made to the composite to modify the microstructure of the in-situ composite. Specimens were then heat treated at 580 °C for homogenization. The as-cast and heat treated in-situ composites were subjected to corrosive media comprising of NaCl + H2O2 solution and the corrosion rate was evaluated by gravimetric weight loss method. Both the as-cast and heat treated in-situ composite were found to be susceptible to intergranular corrosion (IGC), the heat treated specimens being less prone to attack. Optical and scanning electron micrographic observation of the corroded surface revealed highly corroded network in the as-cast in-situ composite. On the contrary, the heat treated composite revealed minimal corrosion network. The rate of corrosion and the IGC network for both the as-cast and heat treated in-situ composite decreases as Mg additions are increased.

  2. Fully spin-polarized two-dimensional electron gas at the CoFe2O4/MgAl2O4(001) polar interface

    NASA Astrophysics Data System (ADS)

    Arras, R.; Calmels, L.

    2014-07-01

    We performed first-principles calculations to show that a fully spin-polarized two-dimensional electron gas can be created at the interface between the polar and insulating spinel oxides CoFe2O4 and MgAl2O4. We give a clear description of the physical parameters (in particular the atomic termination of the interfaces), which favor the formation of this electron gas that is due either to an electric field induced in stoichiometric oxide layers because of their polar character or to a charge reorganization that preserves the global electric neutrality in nonstoichiometric layers. We show that the electric field-induced spin-polarized two-dimensional electron gas can only exist if the thickness of the CoFe2O4 layer is large enough and that it may be destroyed by intermixing at the interfaces.

  3. On the Production of He, Ne, and AR Isotopes from Mg, Al, Si, Ca, Fe, and NI in an Artificially Irradiated Meteoroid

    NASA Astrophysics Data System (ADS)

    Wieler, R.; Signet, P.; Rosel, R.; Herpers, U.; Lupke, M.; Lange, H.-J.; Michel, R.

    1992-07-01

    The production of He, Ne, and Ar isotopes from their main target elements was investigated in an experiment (1) by irradiating a 50-cm-diameter gabbro sphere isotropically with 1.6 GeV protons. The model meteoroid contained, among a large number of other targets, pure element foils of Mg, Al, Si, Fe, and Ni at 10 different depths and wollastonite targets at 3 different depths in central bores. After the irradiation, radionuclide production in these targets was measured by gamma spectrometry. Stable He, Ne, and Ar isotopes were measured in statically operated mass spectrometers. Here, we report the results for stable He, Ne, and Ar isotopes and for ^22Na. The production depth profiles vary widely, ranging from profiles with near-surface production 15% higher than in the center (^22Na from Fe) to such profiles with production in the center 45% higher than near the surface (^20Ne from Mg). The isotope ratios ^3He/^4He and ^3He/^21Ne in Mg, Al, Si and ^22Ne/^21Ne in Mg all decrease significantly with increasing shielding. The production rates of He, Ne, and ^22Na from Mg, Al, and Si in the 1600-MeV simulation experiment are 1.5 to 3 times higher than in the model meteoroid of similar size but irradiated earlier with 600 MeV protons (2). This increase is attributed to the increase of the production of secondary neutrons with primary energies rising from 600 to 1600 MeV. This effect also causes the depth dependences of isotope ratios observed in the 1600-MeV simulation that was not seen in the 600-MeV experiment. Model calculations of the production of He, Ne, and Ar isotopes and of ^22Na were performed for the artificial meteorites of the 600- and 1600 MeV-exposures as well as for real meteoroids. Production rates were calculated from depth-dependent p- and n- spectra, which were derived by Monte Carlo techniques using the HERMES code system (3), and from cross sections for the relevant nuclear reactions as described earlier (4). The cross section database for p

  4. A comparative study of radiation damage in Al{sub 2}O{sub 3}, FeTiO{sub 3}, and MgTiO{sub 3}

    SciTech Connect

    Mitchell, J.N.; Yu, Ning; Sickafus, K.E.; Nastasi, M.; Taylor, T.N.; McClellan, K.J.; Nord, G.L. Jr.

    1995-12-31

    Oriented single crystals of synthetic alpha-alumina ({alpha}-Al{sub 2}O{sub 3}), geikielite (MgTiO{sub 3}) natural ilmenite (FeTiO{sub 3}) were irradiated with 200 keV argon ions under cryogenic conditions (100 K) to assess their damage response. Using Rutherford backscattering spectrometry combined with ion channeling techniques, it was found that ilmenite amorphized readily at doses below 5{times}10{sup 14}, alumina amorphized at a dose of 1-2{times}{sup 15}, and geikielite was amorphized at {approximately}2{times}10{sup 15} Ar cm{sup {minus}2}. The radiation damage response of the ilmenite crystal may be complicated by the presence of hematite exsolution lamellae and the experimentally induced oxidation of iron. The relative radiation-resistance of geikielite holds promise for similar behavior in other Mg-Ti oxides.

  5. 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

  6. Spin state of iron and elastic properties of (MgFe)(SiAl)O3 under conditions of the lower mantle

    NASA Astrophysics Data System (ADS)

    Glazyrin, K.; Boffa Ballaran, T.; Frost, D. J.; McCammon, C. A.; Kantor, A.; Merlini, M.; Hanfland, M.; Dubrovinsky, L. S.

    2012-12-01

    Iron is incorporated into crystal structures of the dominant lower mantle phases, namely, magnesium silicate perovskite (Pv) and ferropericlase (Fp). There is no doubt that iron is the most abundant transition element of the lower mantle. Depending on conditions imposed by the latter, charge distribution between different electronic orbitals of iron may change, giving rise to spin state transitions (SST) which, in turn, may modify bulk elastic and transport properties of the material. Critical conditions promoting SST vary depending on iron cation charge and crystallographic environment. In the case of Pv, it was shown that Fe2+ will occupy exclusively the distorted dodecahedral (A) site, while Fe3+ can substitute in both the A and the B (octahedral) sites. However, the problem becomes more complicated if we consider Fe/Al coupled substitution in Pv and realistic compositions of the lower mantle. Although SST in Pv is a current and highly debated topic, there is clearly a lack of experimental data, and the literature shows strong controversies between theoretical calculations and experiment. The problem of iron SST in Pv is one of the most challenging and important for our understanding of mantle processes and dynamics. We conducted a single crystal diffraction experiment on Mg0.6Fe0.4Si0.63Al0.37O3 Pv at the ID09 beamline, ESRF, Grenoble. Comprehensive characterization of this sample synthesized in a multianvil apparatus revealed that almost all iron in this material is ferric and occupies exclusively the A site (Fe3+A). We studied the combined effect of compression and temperature on the crystal structure and elastic properties of the material, and we observed that (a) below 77 GPa, 1800K there is no SST for Fe3+A and (b) high pressure-high temperature treatment has no effect on Fe/Al cation distribution between different crystallographic sites. These observations are in good agreement with recent theoretical work. Based on a thermal equation of state derived

  7. 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.

  8. 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.

  9. Probing on growth and characterizations of SnFe2O4 epitaxial thin films on MgAl2O4 substrate

    NASA Astrophysics Data System (ADS)

    Gupta, Ram; Candler, J.; Kumar, D.; Gupta, Bipin; Kahol, Pawan

    2014-08-01

    Epitaxial tin ferrite (SnFe2O4) thin films were grown using KrF excimer (248 nm) pulsed laser deposition technique under different growth conditions. Highly epitaxial thin films were obtained at growth temperature of 650 ˚C. The quality and epitaxial nature of the films were examined by X-ray diffraction technique. Furthermore, the phi scans of the film and substrate exhibit four folds symmetry which indicates a cube-on-cube epitaxial growth of the film on MgAl2O4 substrate. Moreover, the magnetic force microscopy measurement shows domains with cluster-like structure which is associated with ferromagnetic phase at room temperature. The coercive field and remnant magnetization of the films decrease with increase in temperature. These high quality ingenious magnetic films could be potentially used in data storage devices.

  10. Ti diffusion in (001) SrTiO3-CoFe2O4 epitaxial heterostructures: blocking role of a MgAl2O4 buffer.

    PubMed

    Rebled, J M; Foerster, M; Estradé, S; Rigato, F; Kanamadi, C; Sánchez, F; Peiró, F; Fontcuberta, J

    2013-11-01

    Titanium diffusion from (001) SrTiO3 (STO) substrates into CoFe2O4 (CFO) films grown using pulsed laser deposition is reported. To elucidate the reasons for Ti interdiffusion, a comparative study of CFO films grown on MgAl2O4 (MAO) and STO substrates, buffered by thin STO and MAO layers, has been made. It is shown that whereas bottom STO layers always result in Ti migration, a thin MAO layer, only 8 nm thick, is effective in blocking it. We argue that this success relies on the lower mobility of Ti ions in the MAO lattice compared to that of CFO. This result should contribute to the development of high quality epitaxial heterostructures of dissimilar complex oxides. PMID:24068072

  11. Modelling Equilibrium and Fractional Crystallization in the System MgO-FeO-CaO-Al2O3-SiO2

    NASA Technical Reports Server (NTRS)

    Herbert, F.

    1985-01-01

    A mathematical modelling technique for use in petrogenesis calculations in the system MgO-FeO-CaO-Al2O3-SiO2 is reported. Semiempirical phase boundary and elemental distribution information was combined with mass balance to compute approximate equilibrium crystallization paths for arbitrary system compositions. The calculation is applicable to a range of system compositions and fractionation calculations are possible. The goal of the calculation is the computation of the composition and quantity of each phase present as a function of the degree of solidification. The degree of solidification is parameterized by the heat released by the solidifying phases. The mathematical requirement for the solution of this problem is: (1) An equation constraining the composition of the magma for each solid phase in equilibrium with the liquidus phase, and (2) an equation for each solid phase and each component giving the distribution of that element between that phase and the magma.

  12. 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.

  13. 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)

  14. 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

  15. 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. PMID:16475357

  16. 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

  17. 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.

  18. Proximity Effect in Nb/Mg/CoFe Trilayers.

    NASA Astrophysics Data System (ADS)

    Choi, Seong Kook; Kwon, Jun Hyung; Char, Kookrin

    2007-03-01

    We have fabricated the Nb/Mg bilayer and Nb/Mg/CoFe trilayer samples by varying Mg layer thickness and measured their superconducting transition temperature Tc electrically using the 4-prove method. Mg normal layer was used to investigate the effect of its small atomic number, since we have observed previously the largely different behavior when Au, Cu and Al were used. When the Al layer was used, a very unusual behavior was found. Because of chemical interaction between Nb and Mg, the Tc transition curves did not show sharp Tc transition. In order to prevent this interaction, we inserted 2 nm thick Al layer between Nb and Mg. In the case of Nb/Al(2nm)/Mg, we observed Tc behavior consistent with a conventional SN theory. In the case of Nb/Al(2nm)/Mg/CoFe with fixed thicknesses of Nb and CoFe layer, the Tc values exhibited two distinct behavior as the thickness of Mg increased. The Tc value of S/N/F trialyer increased rapidly until the Mg thickness reached a few nm. As Mg thickness increased further to 200 nm, the Tc value of S/N/F decreased again, following closely those of the S/N data. Overall, the Mg data basically followed those of Al data, suggesting that the low atomic number of the normal layer is important in observing the unusual proximity effect in SNF trilayers. Our analysis of the interface effect using an Usadel picture will be presented.

  19. 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

  20. 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.

  1. 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).

  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. The role of Pt underlayer on the magnetization dynamics of perpendicular magnetic anisotropy Pt/Co2FeAl0.5Si0.5/MgO

    NASA Astrophysics Data System (ADS)

    Besbas, Jean; Loong, Li Ming; Wu, Yang; Yang, Hyunsoo

    2016-06-01

    We investigate the role of Pt on the magnetization dynamics of Pt/Co2FeAl0.5Si0.5/MgO with perpendicular magnetic anisotropy using the time resolved magneto-optic Kerr effect. Pt/Co2FeAl0.5Si0.5/MgO shows ultrafast magnetization dynamics comparable to 3d ferromagnets and can be fully demagnetized. The demagnetization time τd ˜ 0.27 ps and magnetic heat capacity are independent of the Pt underlayer, whereas the value of the electron-phonon coupling time τe ˜ 0.77 ps depends on the presence of the Pt layer. We further measure the effective damping αeff ˜ 1 that does not scale as the inverse demagnetization time (1/τd), but is strongly affected by the Pt layer.

  4. 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. PMID:26965650

  5. 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.

  6. Synthesis and equation of state of post-perovskites in the (Mg,Fe)[subscript 3]Al[subscript 2]Si[subscript 3]O[subscript 12] system

    SciTech Connect

    Shieh, Sean R.; Dorfman, Susannah M.; Kubo, Atsushi; Prakapenka, Vitali B.; Duffy, Thomas S.

    2012-02-06

    The formation and properties of the post-perovskite (CaIrO{sub 3}-type) phase were studied in Fe-rich compositions along the pyrope-almandine ((Mg,Fe){sub 3}Al{sub 2}Si{sub 3}O{sub 12}) join. Natural and synthetic garnet starting materials with almandine fractions from 38 to 90 mol% were studied using synchrotron X-ray diffraction in the laser-heated diamond anvil cell. Single-phase post-perovskite could be successfully synthesized from garnet compositions at pressures above 148 GPa and temperatures higher than 1600 K. In some cases, evidence for a minor amount of Al{sub 2}O{sub 3} post-perovskite was observed for Alm38 and Alm54 compositions in the perovskite + post-perovskite two-phase region. Pressure-volume data for the post-perovskite phases collected during decompression show that incorporation of Fe leads to a systematic increase of unit cell volume broadly similar to the variation observed in the (Mg,Fe)SiO{sub 3} system. The presence of Al{sub 2}O{sub 3} increases the stability of perovskite relative to post-perovskite, requiring higher pressures (> 148 GPa) for synthesis of pure post-perovskites. Our data together with those of Tateno et al. (2005) also suggest that in the Al-rich system the presence of Fe has no strong effect on the pressure required to synthesize the pure post-perovskite phase, but the two-phase perovskite and post-perovskite region may be broad and its width dependent on Fe content. Our results suggest that any regions highly enriched in Al{sub 2}O{sub 3} may consist of either the perovskite phase or a mixture of perovskite and post-perovskite phases throughout the entire thickness of the D* region. The observed synthesis pressures (> 148 GPa) for a pure post-perovskite phase are beyond that at the Earth's core-mantle boundary ({approx} 135 GPa).

  7. Fabrication and characterization of spin injector using a high-quality B2-ordered-Co2FeSi0.5Al0.5/MgO/Si(100) tunnel contact

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    We successfully fabricate a (100)-orientated B2-type-Co2FeSi0.5Al0.5 (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.

  8. 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.

  9. 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

    2016-04-01

    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.

  10. 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.

  11. 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).

  12. Magnetic anisotropy and order structure of L1{sub 0}-FePt(001) single-crystal films grown epitaxially on (001) planes of MgO, SrTiO{sub 3}, and MgAl{sub 2}O{sub 4} substrates

    SciTech Connect

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

    2014-05-07

    L1{sub 0}–FePt(001) single-crystal films were grown epitaxially on SrTiO{sub 3}(001), MgAl{sub 2}O{sub 4}(001), and MgO(001) substrates. Their uniaxial magnetic anisotropy K{sub u} and the order structure were examined for the film thickness t range of 2–14 nm. All series of films show large K{sub u} of 4 × 10{sup 7} erg/cm{sup 3} in the thickness range higher than 10 nm, with order parameter S of 0.8 and saturation magnetization M{sub s} of 1120 emu/cm{sup 3}. K{sub u} decreased gradually as t decreased. The K{sub u} reduction was considerable when t decreased from 4 nm to 2 nm. No marked difference in the thickness dependence of K{sub u} was found in any series of films, although the lattice mismatch between FePt and the substrates was markedly different. K{sub u} reduction showed good agreement with the reduction of S for the films on MgAl{sub 2}O{sub 4} and MgO. The K{sub u} ∼ S{sup 2} 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. 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.

  14. Investigation of Liquidus Temperatures and Phase Equilibria of Copper Smelting Slags in the FeO-Fe2O3-SiO2-CaO-MgO-Al2O3 System at PO2 10-8 atm

    NASA Astrophysics Data System (ADS)

    Henao, Hector M.; Nexhip, Colin; George-Kennedy, David P.; Hayes, P. C.; Jak, E.

    2010-08-01

    Copper concentrates and fluxes can contain variable levels of SiO2, CaO, and MgO in addition to main components Cu, Fe, and S. Metal recovery, slag tapping, and furnace wall integrity all are dependent on phase equilibria and other properties of the phases and are functions of slag composition and operational temperature. Optimal control of the slag chemistry in the copper smelting, therefore, is essential for high recovery and productivity; this, in turn, requires detailed knowledge of the slag phase equilibria. The present work provides new phase equilibrium experimental data in the FeO-Fe2O3-SiO2-CaO-MgO-Al2O3 system at oxygen partial pressure of 10-8 atm within the range of temperatures and compositions directly relevant to copper smelting. For the range of conditions relevant to the Kennecott Utah Copper (South Magna, UT) smelting furnace, it was confirmed experimentally that increasing concentrations of MgO or CaO resulted in significant decreases of the tridymite liquidus temperature and in changes in the position of the tridymite liquidus in the direction of higher silica concentration; in contrast, the spinel liquidus temperatures increase significantly with the increase of MgO or CaO. Olivine and clinopyroxene precipitates appeared at high MgO concentrations in the liquid slag. The liquidus temperature in the spinel primary phase field was expressed as a linear function of 1/(wt pctFe/wt pctSiO2), wt pctCaO, wt pctMgO, and wt pctAl2O3. The positions of each of the liquidus points (wt pctFe)/(wt pctSiO2) at a fixed temperatures in the tridymite primary phase field were expressed as linear functions of wt pctCaO, wt pctMgO, and wt pctAl2O3.

  15. Rapidly solidified NiAl and FeAl

    NASA Technical Reports Server (NTRS)

    Gaydosh, D. J.; Crimp, M. A.

    1984-01-01

    Melt spinning was used to produce rapidly solidified ribbons of the B2 intermetallics NiAl and FeAl. Both Fe-40Al and Fe-45Al possessed some bend ductility in the as spun condition. The bend ductility of Fe-40Al, Fe-45Al, and equiatomic NiAl increased with subsequent heat treatment. Heat treatment at approximately 0.85 T (sub m) resulted in significant grain growth in equiatomic FeAl and in all the NiAl compositions. Low bend ductility in both FeAl and NiAl generally coincided with intergranular failure, while increased bend ductility was characterized by increasing amounts of transgranular cleavage fracture.

  16. An experimental study of the Fe oxidation states in garnet and clinopyroxene as a function of temperature in the system CaO-FeO-Fe2O3-MgO-Al2O3-SiO2: implications for garnet-clinopyroxene geothermometry

    NASA Astrophysics Data System (ADS)

    Purwin, Horst; Lauterbach, Stefan; Brey, Gerhard P.; Woodland, Alan B.; Kleebe, Hans-Joachim

    2013-04-01

    Samples with eclogitic composition in the system CaO-FeO-Fe2O3-MgO-Al2O3-SiO2 were produced from various kinds of starting materials held in graphite-lined Pt capsules at a pressure of 2.5-3.0 GPa and temperatures of 800-1,300 °C using a piston-cylinder or Belt apparatus. Garnets and clinopyroxenes were characterized by analytical transmission electron microscopy and electron probe micro-analysis (EPMA). Fe3+/ΣFe ratios determined by electron energy-loss spectroscopy (EELS) decrease in clinopyroxene from 22.2 ± 3.4 % at 800 °C to 13.3 ± 5.4 % at 1,300 °C, while in garnet, they vary between 10.8 ± 1.5 and 15.4 ± 4.7 %, respectively. Temperature estimates according to Krogh (Contrib Mineral Petrol 99:44-48, 1988) reproduce the experimental temperature to ±60 °C without systematic deviations if total iron is used in the calculation. If only the Fe2+ content is used, which was obtained by combining EPMA and EELS results, the experimental temperature is underestimated by 33 °C on average at 800-1,200 °C and overestimated by 77 °C on average at 1,300 °C. These systematic deviations can be explained by the temperature-dependent ratio of Fe2+/ΣFe in garnet divided by that in clinopyroxene. Since the difference between the calculated and experimental temperature is relatively small, a Fe2+-based recalibration of the thermometer appears not to be necessary for the investigated system in the range of pressure, temperature and composition covered by the experiments of this study.

  17. 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.

  18. Influence of RCS on Al-3Mg and Al-3Mg-0.25Sc alloys

    NASA Astrophysics Data System (ADS)

    Bhovi, Prabhakar M.; Venkateswarlu, K.

    2016-02-01

    An influence of repetitive corrugation and straightening (RCS) was studied on Al-3Mg and Al-3Mg-0.25Sc alloys up to eight passes. Each pass consist of a corrugation and followed by straightening. This has resulted in introducing large plastic strain in sample, and thus led to formation of sub-micron grain sizes with high angle grain boundaries. These sub grain formation was eventually resulted in improved mechanical properties. The average grain size of Al-3Mg-0.25Sc alloy after 8 passes yielded to ∼0.6pm. Microhardness, strength properties were evaluated and it suggests that RCS was responsible for high hardness values as compared to the as cast samples. The microhardness values after RCS were 105 HV and 130 HV for Al-3Mg and Al-3Mg-0.25Sc alloys, respectively. Similarly, ∼ 40% improvement in tensile strength from 240 MPa to 370 MPa was observed for Al- 3Mg-0.25Sc alloy after RCS process.Al-3Mg and Al-3Mg-0.25Scalloys exhibited maximum strength of 220 MPa and 370 MPa, respectively. It is concluded that RCS process has a strong influence on Al- 3Mg and Al-3Mg-0.25Sc alloys for obtaining improved mechanical properties and grain refinement. In addition to RCS process and presence of AESc precipitates in Al-3Mg-0.25Sc alloy had a significant role in grain refinement and improved mechanical properties as compared to Al-3Mg alloy.

  19. 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.

  20. 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.

  1. A thermodynamic model for di-trioctahedral chlorite from experimental and natural data in the system MgO-FeO-Al2O3-SiO2-H2O: applications to P- T sections and geothermometry

    NASA Astrophysics Data System (ADS)

    Lanari, Pierre; Wagner, Thomas; Vidal, Olivier

    2014-02-01

    We present a new thermodynamic activity-composition model for di-trioctahedral chlorite in the system FeO-MgO-Al2O3-SiO2-H2O that is based on the Holland-Powell internally consistent thermodynamic data set. The model is formulated in terms of four linearly independent end-members, which are amesite, clinochlore, daphnite and sudoite. These account for the most important crystal-chemical substitutions in chlorite, the Fe-Mg, Tschermak and di-trioctahedral substitution. The ideal part of end-member activities is modeled with a mixing-on-site formalism, and non-ideality is described by a macroscopic symmetric (regular) formalism. The symmetric interaction parameters were calibrated using a set of 271 published chlorite analyses for which robust independent temperature estimates are available. In addition, adjustment of the standard state thermodynamic properties of sudoite was required to accurately reproduce experimental brackets involving sudoite. This new model was tested by calculating representative P- T sections for metasediments at low temperatures (<400 °C), in particular sudoite and chlorite bearing metapelites from Crete. Comparison between the calculated mineral assemblages and field data shows that the new model is able to predict the coexistence of chlorite and sudoite at low metamorphic temperatures. The predicted lower limit of the chloritoid stability field is also in better agreement with petrological observations. For practical applications to metamorphic and hydrothermal environments, two new semi-empirical chlorite geothermometers named Chl(1) and Chl(2) were calibrated based on the chlorite + quartz + water equilibrium (2 clinochlore + 3 sudoite = 4 amesite + 4 H2O + 7 quartz). The Chl(1) thermometer requires knowledge of the (Fe3+/ΣFe) ratio in chlorite and predicts correct temperatures for a range of redox conditions. The Chl(2) geothermometer which assumes that all iron in chlorite is ferrous has been applied to partially recrystallized

  2. 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.

  3. Investigations of zero-field splitting (ZFS) and local distortion parameters of Fe3+ ions doped into three oxi-spinels (ZnAl2O4, MgAl2O4, and ZnGa2O4) by theoretical analysis.

    PubMed

    Açıkgöz, Muhammed

    2011-08-01

    The local environment around the paramagnetic centers formed by the Fe(3+) ions doped into three oxi-spinel crystals (ZnAl(2)O(4), MgAl(2)O(4), and ZnGa(2)O(4)) is investigated utilizing the fourth-order perturbation formula of the axial zero-field splitting parameter D on the basis of the dominant spin-orbit coupling mechanism. In order to fix a plausible cubic space group for B-sites located by Al(3+)/Ga(3+) cations, several modeling approaches are used and the results are discussed in detail. PMID:21524935

  4. Thermoelasticity of Al3+- and Fe3+-bearing bridgemanite

    NASA Astrophysics Data System (ADS)

    Valencia-Cardona, Juan; Shukla, Gaurav; Cococcioni, Matteo; Wentzcovitch, Renata

    2015-03-01

    We present quasi-harmonic LDA+U calculations of thermoelastic properties of Fe3+- and Al3+-bearing bridgemanite (MgSiO3), the main Earth forming phase, at relevant P,T conditions and compositions. Three charge-coupled substitutions, namely, Al3+-Al3+, Fe3+-Fe3+, and Fe3+-Al3+ have been investigated. Aggregate elastic moduli and sound velocities are successfully compared with limited experimental measurements available. The effect of the pressure induced high-spin to low-spin state change in Fe3+ in the B-site has been investigated in great detail since it has potentially dramatic effects on seismic velocities in the Earth's lower mantle. Research supported by NSF/EAR and NSF/CAREER.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Constitution of the Moon: 1. Assessment of thermodynamic properties and reliability of phase relation calculations in the FeO-MgO-Al2O3-SiO2 system

    NASA Astrophysics Data System (ADS)

    Fabrichnaya, O. B.; Kuskov, O. L.

    1994-06-01

    The thermodynamic functions of minerals in the FeO-MgO-Al2O3-SiO2 (FMAS) system have been assessed using phase equilibria, equations of state and calorimetric data. Phase equilibria in this system have been calculated using ideal, symmetric and asymmetric models of solid solution for minerals to obtain KD of exchange reactions consistent with experimental data. A symmetric model for olivine (Wol = 10 800 J mol-1), spinel (Wsp = 1300 J mol-1) and pyroxene (WFeAlopx = WAlFeopx = -3383 - 2.35T - 0.4723P) and an asymmetric model for garnet (WFeMggr = 230 + 0.01P, WMgFegr = 3720 + 0.06P) were recommended, as these mixing parameters provide a better agreement for the calculated phase equilibria with the totality of experimental data. The THERMOSEISM database which includes experimental and assessed data on thermodynamic and thermoelastic properties (bulk modulus and its pressure derivative, thermal expansion, heat capacity, volume, Debye temperature, enthalpy of formation, entropy and mixing parameters of solid solutions), has been obtained for calculation of mineral assemblages at high pressure and temperature and for the further application to the modelling of the mineral composition of the lunar mantle.

  12. 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.

  13. 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.

  14. The atomic and electronic structure of the FeCoB/MgO interface

    NASA Astrophysics Data System (ADS)

    Burton, J. D.; Jaswal, S. S.; Tsymbal, E. Y.; Mryasov, O. N.; Heinonen, O. G.

    2006-03-01

    Magnetic tunnel junctions (MTJs) have recently aroused much interest due to their potential applications as random access memories and magnetic field sensors. MTJs consist of a thin insulating layer separating two ferromagnetic electrodes. Very recently FeCoB/MgO/FeCoB MTJs have shown promising results. Upon annealing, the amorphous FeCoB electrodes crystallize in a bcc structure epitaxial to the MgO(001) surface. Many groups have observed a significant increase in TMR ratios (higher than 300% at room temperature [1]) after annealing. It is clear that the crystallization of the electrodes plays an important role in this increase. It is not clear, however, what happens to B after annealing and what role it plays in enhancing TMR. We present results of first-principles total energy calculations that suggest that it is energetically favorable for B to reside at the crystalline FeCoB/MgO interface rather than remain in the bulk of the FeCoB electrode. We also find that the presence of B at the interface significantly weakens bonding between the FeCoB electrode and the MgO barrier. We are investigating the presence of resonant states[2] at the FeCoB/MgO interface and will discuss the effects of interfacial B on them. [1] J. Hayakawa et al., 2005 MMM Conference. [2] Belashchenko et al., Phys. Rev. B 72, R140404 (2005).

  15. Measurement of FeO activity and solubility of MgO in smelting slags

    NASA Astrophysics Data System (ADS)

    Liu, Shih-Hsien; Fruehan, R. J.; Morales, A.; Ozturk, B.

    2001-02-01

    In bath smelting, the FeO activity of the slag must be known to predict the equilibrium of slag-metal reactions and for effective control of the rate of reduction in the system. Also, knowledge of the solubility of MgO in these slags is useful for reducing refractory consumption. A series of measurements of the FeO activity in simulated bath smelting slags (CaO-SiO2-Al2O3-MgOsat-FeO) were conducted by the electromotive force (EMF) technique. The influence of the slag composition on the relationship between the FeO activity coefficient and FeO content was studied. It has been found that the measured FeO activity coefficient decreases with increasing FeO content in the slag and increases slightly with increasing slag basicity, which is defined as (CaO + MgO)/(SiO2 + Al2O3) on a mole fraction basis. The measured values of the FeO activity coefficient are in reasonable agreement with previously published data. The solubility of MgO was also measured and found to rang from 16 to 30 pct and decrease with increasing basicity.

  16. 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

  17. Measurement and Modeling of the Production of He, Ne, and AR from Mg, Al, Si, Fe, and NI in an Artificial Iron Meteoroid Irradiated Isotropically with 1.6 GeV Protons

    NASA Astrophysics Data System (ADS)

    Busemann, H.; Wieler, R.; Leya, I.; Lange, H.-J.; Michel, R.; Meltzow, B.; Herpers, U.

    1995-09-01

    The production by GCR protons of He, Ne and Ar isotopes from their main target elements was investigated in a simulation experiment [1] by irradiating a 20-cm diameter iron sphere isotropically with 1.6 GeV protons. The model-meteoroid contained, among other targets, pure Mg, Al, Si, Fe, and Ni foils at various depths in central bores. Radionuclide production in these targets was measured by gamma-spectrometry. Stable He, Ne, and Ar isotopes were measured by mass spectrometry. These latter results and the ^22Na data are reported here. As in our earlier simulation with a 50-cm diameter gabbro sphere irradiated with 1.6 GeV protons [2], the present experiment simulates the exposure of meteoroids to galactic protons in space within about 20%, if normalized to the same number of particles. Some systematic deviations are attributed to differences between the monoenergetic irradiation and the exposure to the GCR spectrum and to resulting differences between the secondary particle fields. A comparison of the new production rates with those obtained in the gabbro sphere [2] clearly exhibits the influence of bulk chemical composition on production rates which was discovered earlier by Begemann and Schultz [3] in stony irons. Model calculations of the production of He, Ne, Ar, and ^22Na were performed for all artificial iron and stony meteoroids irradiated by our collaboration [2, 4, 5, this work]. Production rates were calculated from depth-dependent p- and n-spectra derived by Monte Carlo techniques using the HERMES code system [6] and from cross sections for the relevant nuclear reactions. For p-induced reactions all available experimental thin-target cross sections were used [2]. Cross sections for n-induced reactions were calculated by the new AREL code [7] which is a relativistic version of the hybrid model of preequilibrium reactions [8]. In addition to these a priori calculations a posteriori model calculations were performed. Theoretical cross sections for n

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Formation and Thermodynamics of Mg-Al-Ti-O Complex Inclusions in Mg-Al-Ti-Deoxidized Steel

    NASA Astrophysics Data System (ADS)

    Ren, Ying; Zhang, Lifeng; Yang, Wen; Duan, Haojian

    2014-12-01

    The formation of Mg-Al-Ti-O complex inclusions in steel was investigated by laboratory experiments and thermodynamic calculation. The composition evolutions of Mg-Al-Ti-O inclusions in steel with different contents of [Al], [Mg], and [Ti] were discussed. Mg-Al-Ti-O complex inclusion with high TiOx content was liquid at 1873 K (1600 °C), indicating MgAl2O4 spinel inclusions can be modified to low melting temperature ones by combining TiOx component. The stability diagram of Al-Mg-Ti-O system inclusions in the molten steel at 1873 K (1600 °C) was calculated, considering many kinds of oxide inclusions such as MgO, Al2O3, TiOx, MgTi2O4, MgAl2O4, Al2TiO5, and liquid inclusion. The thermodynamic calculations are in good agreement with experimental results, which can predict the formation of Al-Mg-Ti-O complex inclusions in molten steel with a large concentration range of [Al], [Mg], and [Ti].

  3. 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.

  4. 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.

  5. 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

  6. An internally consistent model for the thermodynamic properties of Fe-Mg-titanomagnetite-aluminate spinels

    NASA Astrophysics Data System (ADS)

    Sack, Richard O.; Ghiorso, Mark S.

    1991-02-01

    A model is developed for the thermodynamic properties of Fe2+-Mg2+-aluminate-titanate-ferrite spinels of space group Fd3m. The model incorporates an expression for the configurational entropy of mixing which accounts for long-range order over tetrahedral and octahedral sites. Short-range order or departures from cubic symmetry are not considered. The non-configurational Gibbs energy is formulated as a second degree Taylor expansion in six linearly independent composition and ordering variables. The model parameters are calibrated to reproduce miscibility gap constraints, order-disorder phenomena in MgAl2O4 and MgFe2O4, and Fe2+-Mg2+ partitioning data between olivine and: (1) aluminate spinels; (2) ferrite spinels; (3) titanate spinels; (4) mixed aluminate-ferrite spinels. This calibration is achieved without invoking non-configurational excess entropies of mixing. The model predicts that the ordering state of FeAl2O4 is more normal than that of MgAl2O4. It also successfully accounts for heat of solution measurements and activity-composition relations in the constituent binaries. Phase equilibrium constraints require that the structure of Fe3O4 is more inverse than random at all temperatures and that Mg2+ has a strong tetrahedral site preference with respect to that of Fe2+. The analysis suggests that in the titanates short range order on octahedral sites may be significant at temperatures as high as 1300° C. Constraints developed from calibrating the thermodynamic properties of Fe2+-Mg2+-aluminatetitanate-ferrite spinel solid solutions permit extension of the database of Berman (1988) to include estimates of the end-member properties of hercynite (FeAl2O4), ulvöspinel (Fe2TiO4), MgFe2O4 and cubic Mg2TiO4. In constructing these estimates, provision is made for low-temperature magnetic entropy contributions and the energetic consequences of disordering the aluminates and the ferrites. These estimates are consistent with all of the available low

  7. 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.

  8. On the crack growth resistance and strength of the B2 iron aluminides Fe-40Al, Fe-45Al, and Fe-10Ni-40Al (at. %)

    SciTech Connect

    Schneibel, J.H.; Maziasz, P.J.

    1994-09-01

    The crack growth resistance and yield strength of the B2 iron aluminides Fe-40Al, Fe-45Al, are Fe-10Ni-40Al (at. %) have been investigated at room temperature laboratory air. After fast cooling from 1273 K, Fe-45Al and Fe-10Ni-40Al are much stronger than Fe-40Al, and exhibit considerably lower crack growth resistance. The crack growth resistance decreases with decreasing crack propagation velocity. Low crack propagation velocities favor intergranular fracture, whereas high velocities can lead to significant contributions from transgranular fracture. Boron additions to Fe-40Al and Fe-10Ni-40Al improve the crack growth resistance, reduce its dependence on the crack propagation velocity, and cause the path to be predominantly transgranular. In a plot of fracture toughness versus yield strength, the properties of the iron aluminides are similar to those of typical aluminum alloys.

  9. 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.

  10. 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.

  11. Diffusion kinetics of Fe 2+ and Mg in aluminous spinel . experimental determination and applications

    NASA Astrophysics Data System (ADS)

    Liermann, Hanns-Peter; Ganguly, Jibamitra

    2002-09-01

    The diffusion coefficients of Fe 2+ and Mg in aluminous spinel at ˜20 kb, 950 to 1325°C, and at 30 kb, 1125°C have been determined via diffusion couple experiments and numerical modeling of the induced diffusion profiles. The oxygen fugacity, fO 2, was constrained by graphite encapsulating materials. The retrieved self-diffusion coefficients of Fe 2+ and Mg at ˜20 kb, 950 to 1325°C, fit well the Arrhenian relation, D = D 0exp(-Q/RT), where Q is the activation energy, with D 0(Fe) = 1.8 (±2.8) × 10 -5, D 0(Mg) = 1.9 (±1.4) × 10 -5 cm 2/s, Q(Fe) = 198 ± 19, and Q(Mg) = 202 ± 8 kJ/mol. Comparison with the data at 30 kb suggests an activation volume of ˜5 cm 3/mol. From analysis of compositional zoning in natural olivine-spinel assemblages in ultramafic rocks, previous reports concluded that D(Fe-Mg) in spinel with Cr/(Cr + Al) ≤0.5 is ˜10 times that in olivine. The diffusion data in spinel and olivine have been applied to the problems of preservation of Mg isotopic inhomogeneity in spinel within the plagioclase-olivine inclusions in Allende meteorite and cooling rates of terrestrial ultramafic rocks.

  12. Thermodynamics and Kinetics of the Formation of Al2O3/ MgAl2O4/MgO in Al-Silica Metal Matrix Composite

    NASA Astrophysics Data System (ADS)

    Sreekumar, V. M.; Ravi, K. R.; Pillai, R. M.; Pai, B. C.; Chakraborty, M.

    2008-04-01

    The formation of Al2O3, MgAl2O4, and MgO has been widely studied in different Al base metal matrix composites, but the studies on thermodynamic aspects of the Al2O3/ MgAl2O4/MgO phase equilibria have been limited to few systems such as Al/Al2O3 and Al/SiC. The present study analyzes the Al2O3/MgAl2O4 and MgAl2O4/MgO equilibria with respect to the temperature and the Mg content in Al/SiO2 system using an extended Miedema model. There is a linear and parabolic variation in Mg with respect to the temperature for MgAl2O4/MgO and Al2O3/MgAl2O4 equilibria, respectively, and the influence of Si and Cu in the two equilibria is not appreciable. The experimental verification has been limited to MgAl2O4/MgO equilibria due to the high Mg content (≥0.5 wt pct) required for composite processing. The study has been carried out on two varieties of Al/SiO2 composites, i.e., Al/Silica gel and Al/Micro silica processed by liquid metallurgy route (stir casting route). MgO is found to be more stable compared to MgAl2O4 at Mg levels ≥5 and 1 wt pct in Al/Silica gel and Al/Micro silica composites, respectively, at 1073 K. MgO is also found to be more stable at lower Mg content (3 wt pct) in Al/Silica gel composite with decreasing particle size of silica gel from 180 micron to submicron and nanolevels. The MgO to MgAl2O4 transformation has taken place through a series of transition phases influenced by the different thermodynamic and kinetic parameters such as holding temperature, Mg concentration in the alloy, holding time, and silica particle size.

  13. Thermal mixing of Al-Fe multilayers

    NASA Astrophysics Data System (ADS)

    Meyer, M.; Mendoza Zélis, L.; Sánchez, F. H.; Traverse, A.

    1994-12-01

    Al-Fe multilayers have been mixed by thermal treatment and their evolution followed by conversion electron Mössbauer spectroscopy. The initial and final states have been characterized by Rutherford backscattering spectrometry. The results are compared with those previously obtained in the ion beam mixing of similar systems.

  14. Structure of epitaxial L10-FePt/MgO perpendicular magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Kohn, Amit; Tal, Nadav; Elkayam, Ayala; Kovàcs, Andras; Li, Dalai; Wang, Shouguo; Ghannadzadeh, Saman; Hesjedal, Thorsten; Ward, Roger C. C.

    2013-02-01

    Perpendicular magnetic tunnel junctions (p-MTJs) with MgO barriers are interesting for high-density information-storage devices. Chemically ordered L10-FePt is a potential electrode due to its large perpendicular magnetocrystalline anisotropy. To-date, a single theoretical study on L10-FePt/MgO p-MTJ based on an idealized structure reported significant dependence of spin-dependent tunneling on interface structure. [Y. Taniguchi et al., IEEE Trans. Magn. 44, 2585 (2008).] We report a structural study of epitaxial L10-FePt(001)[110]//MgO(001)[110]//L10-FePt(001)[110] p-MTJs, focusing on the interfaces using aberration-corrected scanning transmission electron microscopy. Interfaces are semi-coherent, with oxygen atomic-columns of MgO located opposite to iron atomic-columns in L10-FePt. Up to three lattice planes show atomic-column steps, the origin of which is attributed to antiphase boundaries in L10-FePt.

  15. The role of Mg interface layer in MgO magnetic tunnel junctions with CoFe and CoFeB electrodes

    SciTech Connect

    Yang, Hyunsoo; Yang, See-Hun; Parkin, Stuart

    2012-03-15

    The tunneling spin polarization (TSP) is directly measured from reactively sputter deposited crystalline MgO tunnel barriers with various CoFe(B) compositions using superconducting tunneling spectroscopy. We find that the Mg interface layer thickness dependence of TSP values for CoFeB/Mg/MgO junctions is substantially different from those for CoFe/Mg/MgO especially in the pre-annealed samples due to the formation of boron oxide at the CoFeB/MgO interface. Annealing depletes boron at the interface thus requiring a finite Mg interface layer to prevent CoFeOx formation at the CoFeB/MgO interface so that the TSP values can be optimized by controlling Mg thickness.

  16. 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.

  17. Atomic Scale Study of Interfaces Involved in Epitaxial Fe/MgO/Fe Magnetic Tunnel Junctions

    SciTech Connect

    Andrieu, S.; Serra, R.; Bonell, F.; Tiusan, C.; Calmels, L.; Snoeck, E.; Varela del Arco, Maria; Pennycook, Stephen J; Walls, M.; Colliex, C.

    2009-01-01

    Epitaxial Fe/MgO/Fe(001) magnetic tunnel junctions grown by Molecular Beam Epitaxy have been studied by using spatially resolved Electron Energy Loss Spectroscopy (EELS). The structure, the chemical composition as well as the bonding variations across the interfaces were investigated up to the atomic scale.

  18. Spin Torque in Asymmetric CoFeB/MgO/FeB Magnetic Tunnel Junctions

    NASA Astrophysics Data System (ADS)

    Tseng, Hsin-Wei; Li, Yun; Read, John; Ralph, Daniel; Buhrman, Robert

    2012-02-01

    Recent studies have shown that the use of asymmetric electrodes in MTJs can significantly affect spin torque (ST) behavior. We will report on the measurement via spin torque ferromagnetic resonance (ST-FMR) and switching phase diagram (SPD) studies of the in-plane and field-like (out-of-plane) torkance of low resistance, asymmetric IrMn/FeB/MgO/FeCoB) and IrMn/FeCoB/MgO/FeB MTJ nanopillars in the as-grown state (TMR˜22%) and the annealed state (TMR˜90%), and in comparison to that of symmetric counterparts; IrMn/FeB/MgO/FeB) and Ir/Mn/FeCoB/MgO/FeCoB MTJs. For the asymmetric MTJs only,the ST-FMR data show a strong field-like torkance for low voltage bias V that reverses sign when the free and pinned layers are reversed. At the higher V regime explored by the SPD the equivalent linear term in the field-like torque can dominate over the in-plane torque, resulting in either the parallel or antiparallel alignment being favored for both bias polarities, depending on the composition of the free layer.

  19. AlN/Fe/AlN nanostructures for magnetooptic magnetometry

    SciTech Connect

    Lišková-Jakubisová, E. Višňovský, Š.; Široký, P.; Hrabovský, D.; Pištora, J.

    2014-05-07

    AlN/Fe/AlN/Cu nanostructures with ultrathin Fe grown by sputtering on Si substrates are evaluated as probes for magnetooptical (MO) mapping of weak currents. They are considered for a laser wavelength of λ = 410 nm (3.02 eV) and operate at oblique light incidence angles, φ{sup (0)}, to enable detection of both in-plane and out-of-plane magnetization. Their performance is evaluated in terms of MO reflected wave electric field amplitudes. The maximal MO amplitudes in AlN/Fe/AlN/Cu are achieved by a proper choice of layer thicknesses. The nanostructures were characterized by MO polar Kerr effect at φ{sup (0)} ≈ 5° and longitudinal Kerr effect spectra (φ{sup (0)} = 45°) at photon energies between 1 and 5 eV. The nominal profiles were refined using a model-based analysis of the spectra. Closed form analytical expressions are provided, which are useful in the search for maximal MO amplitudes.

  20. 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}.

  1. 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.

  2. 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.

  3. Interface characterization of epitaxial Fe/MgO/Fe magnetic tunnel junctions

    SciTech Connect

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

    2012-01-01

    Following predictions by first-principles theory of huge tunnel magnetoresistance (TMR) effect in epitaxial Fe/MgO/Fe magnetic tunnel junctions (MTJs), measured magnetoresistance (MR) ratio about 200% at room temperature (RT) have been reported in MgO-based epitaxial MTJs. Recently, MR ratio of about 600% has been reported at RT in MgO-based amorphous MTJs with core structure of CoFeB/MgO/CoFeB grown by magnetron sputtering with amorphous CoFeB layers. The sputtered CoFeB/MgO/CoFeB MTJs shows a great potential application in spintronic devices. Although epitaxial structure will probably not be used in devices, it remains an excellent model system to compare theoretical calculations with experimental results and to enhance our understanding of the spin dependent tunneling. Both theoretical calculations and experimental results clearly indicate that the interfacial structure plays a crucial role on coherent tunneling across single crystalMgO barrier, especially in epitaxial MgO-based MTJs grown by molecular beam epitaxy (MBE). Surface X-ray diffraction, Auger electron spectroscopy, X-ray absorption spectra, and X-ray magnetic circular dichroism have been used for interface characterization. However, no consistent viewpoint has been reached, and this is still an open issue. In this article, recent studies on the interface characterization in MgO-based epitaxial MTJs will be introduced, with a focus on research by X-ray photoelectron spectroscopy, high resolution transmission electron microscopy, and spin dependent tunneling spectroscopy.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

    Magnesium/silicon carbide (Mg/SiC) has the potential to be the best-performing reflective multilayer coating 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. 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.

  12. Solidification and Microstructural Evolution of Hypereutectic Al-15Si-4Cu-Mg Alloys with High Magnesium Contents

    NASA Astrophysics Data System (ADS)

    Tebib, M.; Ajersch, F.; Samuel, A. M.; Chen, X.-G.

    2013-09-01

    The low coefficient of thermal expansion and good wear resistance of hypereutectic Al-Si-Mg alloys with high Mg contents, together with the increasing demand for lightweight materials in engine applications have generated an increasing interest in these materials in the automotive industry. In the interests of pursuing the development of new wear-resistant alloys, the current study was undertaken to investigate the effects of Mg additions ranging from 6 to 15 pct on the solidification behavior of hypereutectic Al-15Si-4Cu-Mg alloy using thermodynamic calculations, thermal analysis, and extensive microstructural examination. The Mg level strongly influenced the microstructural evolution of the primary Mg2Si phase as well as the solidification behavior. Thermodynamic predictions using ThermoCalc software reported the occurrence of six reactions, comprising the formation of primary Mg2Si; two pre-eutectic binary reactions, forming either Mg2Si + Si or Mg2Si + α-Al phases; the main ternary eutectic reaction forming Mg2Si + Si + α-Al; and two post-eutectic reactions resulting in the precipitation of the Q-Al5Mg8Cu2Si6 and θ-Al2Cu phases, respectively. Microstructures of the four alloys studied confirmed the presence of these phases, in addition to that of the π-Al8Mg3FeSi6 (π-Fe) phase. The presence of the π-Fe phase was also confirmed by thermal analysis. The morphology of the primary Mg2Si phase changed from an octahedral to a dendrite form at 12.52 pct Mg. Any further Mg addition only coarsened the dendrites. Image analysis measurements revealed a close correlation between the measured and calculated phase fractions of the primary Mg2Si and Si phases. ThermoCalc and Scheil calculations show good agreement with the experimental results obtained from microstructural and thermal analyses.

  13. 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.

  14. The Nature of Interfaces in Al-1050/Al-1050 and Al-1050/Mg-AZ31 Couples Joined by Magnetic Pulse Welding (MPW)

    NASA Astrophysics Data System (ADS)

    Stern, A.; Aizenshtein, M.; Moshe, G.; Cohen, S. R.; Frage, N.

    2013-07-01

    The microstructure and the phase composition of the interfaces of Al-1050/Al-1050 and Al-1050/Mg-AZ31 magnetic pulse welding (MPW) joints were characterized by SEM and TEM analyses. The mechanical properties were tested by nanoindentation. Properties of the Al-1050/Al-1050 interface joint were established. The interface is almost free from Al3Fe precipitates, which are present in the base metal. The hardness value is higher than that of the base metal; however, values of the Young's modulus of the interface and base metal are similar. It was suggested that the interface evolution in the Al-1050/Al-1050 system includes local melting and rapid solidification of the base materials. A wavy shaped heterogeneous interface was detected in the Al-1050/Mg-AZ31 joints. Some areas are free from visible intermetallic phases (IMPs), while others contain pockets of relatively coarse intermetallic precipitates. The presence of a relatively large fraction of globular porosity at the interface indicates that local melting takes place in the course of MPW. TEM characterization of regions free of IMPs at the interface reveals regions consisting of fcc supersaturated Al-Mg solid solution, apparently formed as a result of local mechanical alloying during MPW. In other regions, the composition and structure correspond to the Mg17Al12 phase, which was probably formed by local melting and rapid solidification.

  15. Spin dependent transport in FeCo|MgBO|FeCo magnetic tunnel junctions: Can boron in the oxide region be a good thing?

    NASA Astrophysics Data System (ADS)

    Stewart, Derek

    2009-03-01

    Recent experimental studies on FeCoB/MgO/FeCoB tunnel junctions have shown that boron can diffuse into the oxide region during rf-sputtering and result in the formation of crystalline MgBO regions[1,2]. These tunnel junctions still provide high tunneling magnetoresistance values as well as very low RA products[3]. Using a plane wave-pseudopotential density functional approach, I have examined potential Mg(B) oxides such as Mg2B2O5 (both monoclinic and triclinic) as well at kotoite (Mg3B2O6). Total energy calculations indicate that these oxides should be more stable than the formation of separate regions of MgO and B2O3. Kotoite (Mg3B2O6) also has a boron concentration close to that found in the experimentally grown MgBO regions. In addition, kotoite provides a good lattice match with MgO and could act to template neighboring FeCo into crystalline bcc layers during annealing. This evidence suggests that kotoite is formed during the deposition process. I will also discuss the complex band structure of kotoite (Mg3B2O6) and examine how this will also affect spin dependent transport from the FeCo leads. [1] J. Y. Bae et al., J. Appl. Phys. 99 08T316 (2006) [2] J. C. Read et al., Appl. Phys. Lett. 90 132503 (2007) [3] J. C. Read personal communication

  16. The effect of Ti addition on oxidation behavior of FeAl intermetallic alloy

    SciTech Connect

    Li, D.; Lin, D.

    1997-12-31

    The influence of Ti addition on the high temperature oxidation behaviors of FeAl intermetallic alloys in air at 1,000 C and 1,100 C have been investigated. The oxidation kinetics of FeAl alloys were examined by the weight gain method and oxide products were examined by XRD, SEM, EDS and EPMA. The results showed that the oxidation kinetic curves of both Ti-doped and binary Fe-36.5Al alloys were described as different parabolas followed the formula: ({Delta}W/S){sup 2} = K{sub p}t. The parabolic rate constant, K{sub p} values are about 2.4 and 3.3 mg{sup 2}cm{sup {minus}4}h{sup {minus}1} for Fe-36.5Al alloy and about 1.3 and 2.0 mg{sup 2}cm{sup {minus}4}h{sup {minus}1} for Fe-36.5Al-2Ti alloy when oxidizing at 1,000 C and 1,100 C respectively. The difference between Fe-36.5Al and Fe-36.5Al-2Ti alloy is not only in the surface morphology but also in the phase components. In the surface there is only {alpha}-Al{sub 2}O{sub 3} oxide for the Fe-36.5Al alloy while there are {alpha}-Al{sub 2}O{sub 3} and TiO oxide for the Fe-36.5Al-2Ti alloy. The effects of Ti addition on the oxidation resistance of FeAl alloy were discussed based on the microstructural evidence.

  17. Catalytic Methane Decomposition over Fe-Al2 O3.

    PubMed

    Zhou, Lu; Enakonda, Linga Reddy; Saih, Youssef; Loptain, Sergei; Gary, Daniel; Del-Gallo, Pascal; Basset, Jean-Marie

    2016-06-01

    The presence of a Fe-FeAl2 O4 structure over an Fe-Al2 O3 catalysts is demonstrated to be vital for the catalytic methane decomposition (CMD) activity. After H2 reduction at 750 °C, Fe-Al2 O3 prepared by means of a fusion method, containing 86.5 wt % FeAl2 O4 and 13.5 wt % Fe(0) , showed a stable CMD activity at 750 °C for as long as 10 h. PMID:27159367

  18. 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.

  19. Apollo 15 Mg- and Fe-norites - A redefinition of the Mg-suite differentiation trend

    NASA Technical Reports Server (NTRS)

    Lindstrom, M. M.; Marvin, U. B.; Mittlefehldt, D. W.

    1989-01-01

    The Apollo 15 highland rocks from the Apennine Front include clasts of mafic plutonic rocks from deep in the lunar crust that were brought to the surface by the Imbrium and Serenitatis impacts. The Apollo 15 norites exhibit wide variations in mineral and bulk compositions and include Fe-norites that plot between the three major pristine rock fields on a diagram of Mg' in mafic minerals vs An in paglioclase. Based on assemblages and compositions of minerals, and on ratios of elemental abundances, it is concluded that these Apollo 15 Fe-norites are differentiated members of the Mg-norite suite. The Apollo 15 and 17 norites and troctolites form a closely related suite of rocks, whose variations in mineral compositions represent the main differentiation trend of the Mg-suite. This trend in mineral compositions has a steeper slope than the previous Mg-suite field. The parent magmas for these Mg-suite rocks formed by partial melting deep in the lunar mantle. Differentiation by fractional crystallization may also have included assimilation of crustal components as the magmas rose from the mantle and crystallized plutons in the lower crust.

  20. Effect of interfacial structures on spin dependent tunneling in epitaxial L10-FePt/MgO/FePt perpendicular magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    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.

    2015-02-01

    Epitaxial FePt(001)/MgO/FePt magnetic tunnel junctions with L10-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.

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. Inverse and oscillatory magnetoresistance in Fe(001)/MgO/Cr/Fe magnetic tunnel junctions

    SciTech Connect

    Zhang, J.; Wang, Y.; Zhang, Xiaoguang; Han, Prof. X. F.

    2010-01-01

    The effect of Cr(001) insertion layers in Fe(001)/MgO/Cr/Fe magnetic tunneling junctions (MTJs) is studied from first-principles. It is shown that with the increase of the Cr(001) layer thickness, the tunneling magnetoresistance (TMR) first decreases rapidly and then oscillates with a two-monolayer period. At some thicknesses, the oscillation leads to a sign reversal of the TMR. The oscillatory interfacial Cr moment at the Cr-MgO interface as a function of the Cr layer thickness, which arises from the layer-anti-ferromagnetic ordering of Cr, is the cause for the oscillatory TMR.

  6. Ferromagnetic Fe2CrAl Nanowires

    NASA Astrophysics Data System (ADS)

    Dulal, Rajendra; Dahal, Bishnu; Pegg, Ian L.; Philip, John

    Heusler alloy Fe2CrAl (FCA) nanowires were grown on silicon substrates. Nanowires have diameters in the range 50 to 200 nm and lengths up to 100 µm. They exhibit cubic L21 and A2 type structure with a space group, Pm m. Magnetic characterization reveals that they display ferromagnetic behavior and has a Curie temperature above 400 K. Magnetic behavior of FCA nanowires is different from the reported bulk behavior. Bulk FCA with L21 structure has a Curie temperature around 274 K. National Science Foundation under ECCS-0845501 and NSF-MRI, DMR-0922997.

  7. 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. PMID:26636472

  8. 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.

  9. Magnetic, luminescent Eu-doped Mg-Al layered double hydroxide and its intercalation for ibuprofen.

    PubMed

    Wang, Jun; Zhou, Jideng; Li, Zhanshuang; Song, Yanchao; Liu, Qi; Jiang, Zhaohua; Zhang, Milin

    2010-12-27

    A magnetic, luminescent Eu-doped Mg-Al layered double hydroxide with ibuprofen (IBU) intercalated in the gallery has been successfully prepared by a simple coprecipitation method. The physicochemical properties of the samples were well characterized by powder XRD, TEM, FTIR, TGA, inductively coupled plasma MS (ICP-MS), vibrating sample magnetometry (VSM), and fluorospectrophotometry. The results revealed that Fe(3)O(4) nanoparticles are coated on the surface of layered double hydroxides and the obtained (Mg(2)Al(0.95)Eu(0.05))(Fe)-(IBU) sample exhibits both superparamagnetic and luminescent properties, with a saturation magnetization value of 1.86 emu  g(-1) and a strong emission band at 610 nm, respectively. Additionally, it was found that the ibuprofen loading amount is about 31 % (w/w), and the intercalated ibuprofen possesses sustained release behavior when the magnetic, luminescent composite is immersed in simulated body fluid (SBF). PMID:21038324

  10. First-Principles Study of Enhanced Magnetoelectric Effects at the Fe/MgO(001) Interface

    NASA Astrophysics Data System (ADS)

    Niranjan, M. K.; Jaswal, S. S.; Tsymbal, E. Y.; Duan, C.-G.

    2010-03-01

    The magnetoelectric effect allows affecting magnetic properties of materials by electric fields with potential for technological applications such as electrically controlled magnetic data storage. In this study we explore, using first-principles methods, the magnetoelectric effect at the Fe/MgO(001) interface^,1. By explicitly introducing an electric field in our density-functional calculations we demonstrate that the magnetic moment of Fe atoms at the interface changes linearly as a function of the applied electric field with the surface magnetoelectric coefficient being strongly enhanced as compared to that for the clean Fe(001) surface.^1 The effect originates from the increased screening charge associated with a large dielectric constant of MgO. The influence of electric field on relative occupancy of the Fe-3d orbitals leads to significant change in the surface magnetocrystalline anisotropy. These results are compared with the available experimental work.^2 Our results indicate that using high-k dielectrics at the interface with ferromagnetic metals may be very effective in controlling the magnetic properties by electric fields thereby leading to interesting device applications. ^1 C.-G. Duan et al., Phys. Rev. Lett. 101, 137201 (2008). ^2 T. Maruyama et al., Nat. Nanotech., 4, 158 (2009).

  11. 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.

  12. Very low sound velocities in iron-rich (Mg,Fe)O: Implications for the core-mantle boundary region

    NASA Astrophysics Data System (ADS)

    Wicks, J. K.; Jackson, J. M.; Sturhahn, W.

    2010-12-01

    Seismic observations near the base of the core-mantle boundary have revealed 5-20 km thick patches in which the seismic wave velocities are reduced by up to 30%. These ultra-low velocity zones (ULVZs) have previously been attributed to partial melting, a metal-bearing layer (e.g. Knittle and Jeanloz, 1991), or to an iron-enriched post-perovskite phase (Mao et al., 2006). These scenarios all require concomitant iron enrichment to maintain the appropriate densities of these structures. Recent experiments have shown that (Mg,Fe)O is the preferred phase for equilibrium iron partitioning under deep Earth conditions (e.g. Sakai et al., 2010). We propose that in iron-rich assemblages, such as those suggested at the base of the mantle (e.g. Labrosse et al., 2007), the characteristic low sound speeds can be attributed to iron-rich (Mg,Fe)O (Wicks et al., 2010). We present the sound velocities of (Mg.16Fe.84)O measured to 121 GPa at ambient temperature, using nuclear resonant inelastic x-ray scattering. The effect of the electronic environment of the iron sites on the sound velocities were tracked in situ using synchrotron Mössbauer spectroscopy. We found the sound velocities of (Mg.16Fe.84)O to be much lower than those in other presumed mantle phases at similar conditions, most notably at very high pressures. Conservative estimates of the effect of temperature and dilution on aggregate sound velocities show that only a small amount of iron-rich (Mg,Fe)O can greatly reduce the average sound velocity of an assemblage. References: Knittle, E., and Jeanloz, R., Science, 33, L02310 (1991). Labrosse, S. et al., Nature, 450, 866--869 (2007). Mao, W. L. et al., Science, 312, 564--565 (2006). Sakai, T. et al., Phys. Chem. Min., 37, 487--96 (2010). Wicks, J. K., et al., Geophys. Res. Lett., 37, L15304 (2010).

  13. Whole-rock 26Al-26Mg systematics of amoeboid olivine aggregates from the oxidized CV3 carbonaceous chondrite Allende

    NASA Astrophysics Data System (ADS)

    Olsen, M. B.; Krot, A. N.; Larsen, K.; Paton, C.; Wielandt, D.; Schiller, M.; Bizzarro, M.

    2011-11-01

    We report on mineralogy, petrography, and whole-rock 26Al-26Mg systematics of eight amoeboid olivine aggregates (AOAs) from the oxidized CV chondrite Allende. The AOAs consist of forsteritic olivine, opaque nodules, and variable amounts of Ca,Al-rich inclusions (CAIs) of different types, and show evidence for alteration to varying degrees. Melilite and anorthite are replaced by nepheline, sodalite, and grossular; spinel is enriched in FeO; opaque nodules are replaced by Fe,Ni-sulfides, ferroan olivine and Ca,Fe-rich pyroxenes; forsteritic olivine is enriched in FeO and often overgrown by ferroan olivine. The AOAs are surrounded by fine-grained, matrix-like rims composed mainly of ferroan olivine and by a discontinuous layer of Ca,Fe-rich silicates. These observations indicate that AOAs experienced in situ elemental open-system iron-alkali-halogen metasomatic alteration during which Fe, Na, Cl, and Si were introduced, whereas Ca was removed from AOAs and used to form the Ca,Fe-rich silicate rims around AOAs. The whole-rock 26Al-26Mg systematics of the Allende AOAs plot above the isochron of the whole-rock Allende CAIs with a slope of (5.23 ± 0.13) × 10-5 reported by Jacobsen et al. (2008). In contrast, whole-rock 26Al-26Mg isotope systematics of CAIs and AOAs from the reduced CV chondrite Efremovka define a single isochron with a slope of (5.25± 0.01) × 10-5 (Larsen et al. 2011). We infer that the excesses in 26Mg* present in Allende AOAs are due to their late-stage open-system metasomatic alteration. Thus, the 26Al-26Mg isotope systematics of Allende CAIs and AOAs are disturbed by parent body alteration processes, and may not be suitable for high-precision chronology of the early solar system events and processes.

  14. 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.

  15. 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.

  16. 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.

  17. Characteristics of laser welded wrought Mg-Al-Mn alloy

    SciTech Connect

    Quan Yajie Chen Zhenhua; Yu Zhaohui; Gong Xiaosan; Li Mei

    2008-12-15

    Magnesium alloys have gained increased attention in recent years as a structural metal because of their property merits, which necessitates the development of welding techniques qualified for applications in the aeronautic and automotive industries. Laser welding is known to be an excellent method for joining metals. In this paper, a 3 kW CO{sub 2} laser beam was used to weld the wrought Mg-Al-Mn alloy. The characteristics of the microstructure and the mechanical properties of the joints were analyzed by optical microscopy (OM), energy dispersive spectrometry (EDS), scanning electron microscopy (SEM), tensile testing and hardness testing. The experimental results show that the wrought Mg-Al-Mn alloy can be joined successfully using optimized welding conditions. The results of tensile testing show that the highest ultimate tensile strength (UTS) of the joints is up to 94% of that of the base metal. The base metal consists of a typical rolled structure, the narrow heat affected zone (HAZ) has no obvious grain coarsening, and the fusion zone consists of fine grains with a high density of {gamma}-Mg{sub 17}Al{sub 12} precipitates. The hardness test results indicate that the microhardness in the fusion zone is higher than that of the base metal. The elemental analysis reveals that the Mg content in the weld is lower than that of the base metal, but the Al content is slightly higher.

  18. 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.

  19. 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.

  20. Synthetic gedrite: a stable phase in the system MgO-Al2O3-SiO2-H2O (MASH) at 800°C and 10kbar water pressure, and the influence of FeNaCa impurities

    NASA Astrophysics Data System (ADS)

    Fischer, H.; Schreyer, W.; Maresch, W. V.

    Seeded, solid-media piston-cylinder runs of unusually long duration up to 31 days indicate growth or persistence of synthetic gedrite of the composition □Mg6Al[AlSi7O22](OH)2(=6:1:7), prepared from the purest chemicals available, at 10kbar water pressure and 800°C. Conversely, breakdown was observed at 11kbar and 850°C to aluminous enstatite, Al2SiO5, and a melt of the composition MgO.Al2O3.8SiO2. Thus, pure gedrite free of iron, sodium, and calcium is likely to have only a small PT stability field in the MASH system, estimated as 10+/-1kbar, 800+/-20°C, even though metastable growth of gedrite can be observed over a larger PT range. A second starting material with the anhydrous composition 5MgO . 2Al2O3 . 6SiO2 also yielded gedrite of the composition 6:1:7, together with more aluminous phases such as kyanite, corundum or sapphirine, thus suggesting that the end-member gedrite defined as □Mg5Al2[Al2Si6O22](OH)2(=5:2:6) by the IMA Commission on New Minerals and Mineral Names probably does not exist. With the use of this second starting material, which contains FeNaCa impurities, growth of 6:1:7-gedrite was observed over a still wider PT-range. Seeded runs indicate that the true stability field of such slightly impure 6:1:7-gedrites may also be larger than that of the pure MASH phase and extend at least to 15kbar, 800°C. There is, thus, a remarkable stabilization effect on the orthoamphibole structure by impurities amounting only to a total of less than one weight percent of oxides in the starting material. The gedrites synthesized are structurally well ordered amphiboles nearly free of chain multiplicity faults, as revealed by HRTEM. The X-ray diffraction work on the gedrites synthesized yielded the smallest cell volume yet reported for this phase. The small stability field of the pure MASH gedrite is intersected by the upper pressure stability limit of hydrous cordierite for excess-H2O conditions, thus leading to complicated phase relations for both gedrite

  1. Asymmetric angular dependence of spin-transfer torques in CoFe/Mg-B-O/CoFe magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Tang, Ling; Xu, Zhi-Jun; Zuo, Xian-Jun; Yang, Ze-Jin; Gao, Qing-He; Linghu, Rong-Feng; Guo, Yun-Dong

    2016-04-01

    Using a first-principles noncollinear wave-function-matching method, we studied the spin-transfer torques (STTs) in CoFe/Mg-B-O/CoFe(001) magnetic tunnel junctions (MTJs), where three different types of B-doped MgO in the spacer are considered, including B atoms replacing Mg atoms (Mg3BO4), B atoms replacing O atoms (Mg4BO3), and B atoms occupying interstitial positions (Mg4BO4) in MgO. A strong asymmetric angular dependence of STT can be obtained both in ballistic CoFe/Mg3BO4 and CoFe/Mg4BO4 based MTJs, whereas a nearly symmetric STT curve is observed in the junctions based on CoFe/Mg4BO3. Furthermore, the asymmetry of the angular dependence of STT can be suppressed significantly by the disorder of B distribution. Such skewness of STTs in the CoFe/Mg-B-O/CoFe MTJs could be attributed to the interfacial resonance states induced by the B diffusion into MgO spacer.

  2. 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.

  3. 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

  4. 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.

  5. FeAl underlayers for CoCrPt thin film longitudinal media

    SciTech Connect

    Lee, L.; Laughlin, D.E.; Lambeth, D.N.

    1997-04-01

    B2 ordered FeAl films with a small, uniform grain size have been produced by rf diode sputter deposition on glass substrates. CoCrPt films grown on FeAl underlayers were found to have the (10{bar 1}0) lamellar texture. The in-plane coercivities (H{sub c}) of the CoCrPt/FeAl films are comparable to those of the CoCrPt/Cr films and they can be further improved by inserting a thin Cr intermediate layer between the CoCrPt and the FeAl layers. By employing a MgO seed layer or a (002) textured Cr seed layer, (001) textured FeAl can be obtained. However, the (001) FeAl underlayer only induces a weak (11{bar 2}0) textured CoCrPt. Thus no improvement in H{sub c} over those produced on unseeded FeAl underlayers was observed. {copyright} {ital 1997 American Institute of Physics.}

  6. Long range order and vacancy properties in Al-rich Fe{sub 3}Al and Fe{sub 3}Al(Cr) alloys

    SciTech Connect

    Kim, S.M.; Morris, D.G.

    1998-05-01

    Neutron powder diffraction measurements have been carried out in situ from room temperature to about 100 C in Fe28Al (28 at.% Al), Fe32.5Al (32.5 at.% Al) and Fe28Al15Cr (28 at.% Al, 5 at.% Cr) alloys. X-ray diffraction and TEM studies provided supporting information. The data were analyzed to obtain information about the temperature dependence of the DO{sub 3} and B2 long range order parameters, the location of the Cr atoms and their effect on the ordering energies, and on the vacancy formation and migration properties in Fe28Al and Fe32.5Al alloys. The location of the ternary alloying addition in DO{sub 3} and B2 ordered Al-rich Fe{sub 3}Al is shown to be consistent with considerations of interatomic bond energies.

  7. 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.

  8. FeGa/MgO/Fe/GaAs(001) magnetic tunnel junction: Growth and magnetic properties

    NASA Astrophysics Data System (ADS)

    Gobaut, B.; Ciprian, R.; Salles, B. R.; Krizmancic, D.; Rossi, G.; Panaccione, G.; Eddrief, M.; Marangolo, M.; Torelli, P.

    2015-06-01

    Research on spintronics and on multiferroics leads now to the possibility of combining the properties of these materials in order to develop new functional devices. Here we report the integration of a layer of magnetostrictive material into a magnetic tunnel junction. A FeGa/MgO/Fe heterostructure has been grown on a GaAs(001) substrate by molecular beam epitaxy (MBE) and studied by X-ray magnetic circular dichroism (XMCD). The comparison between magneto optical Kerr effect (MOKE) measurements and hysteresis performed in total electron yield allowed distinguishing the ferromagnetic hysteresis loop of the FeGa top layer from that of the Fe buried layer, evidencing a different switching field of the two layers. This observation indicates an absence of magnetic coupling between the two ferromagnetic layers despite the thickness of the MgO barrier of only 2.5 nm. The in-plane magnetic anisotropy has also been investigated. Overall results show the good quality of the heterostructure and the general feasibility of such a device using magnetostrictive materials in magnetic tunnel junction.

  9. 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

  10. Superplasticity in a thermomechanically processed High-Mg, Al-Mg alloy

    NASA Astrophysics Data System (ADS)

    McNelley, T. R.; Lee, E. W.; Mills, M. E.

    1986-06-01

    Superplastic elongations in excess of 400 pct have been observed in tension testing at 573 K (300 °C) and strain rate έ = 2 × 10-3 s-1 for a thermomechanically processed Al-10.2 pct Mg-0.52 pct Mn alloy. The thermomechanical processing consists of solution treatment and hot working, followed by extensive warm rolling at 573 K (300 °C), a temperature below the solvus for Mg in the alloy. This processing results in a fine subgrain structure in conjunction with refined and homogeneously distributed β(Al8Mg5) and MnAl6 precipitates. This structure does not statically recrystallize when annealed at 573 K (300 °C) but appears to recrystallize continuously during deformation at such a temperature and the resulting fine grain structure deforms with minimal cavitation. At temperatures above the Mg-solvus, e.g., 673 K (400 °C), recrystallization and growth occur readily resulting in rela tively coarser structures which deform superplastically but with extensive grain boundary sliding and cavitation.

  11. {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.

  12. 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

  13. 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.

  14. 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.

  15. Hydrogen generation by means of catalyzed Mg-Al hydrolysis

    NASA Astrophysics Data System (ADS)

    Hoehne, K.; Jaeger, P.

    Based on considerations of reactivity, costs, and the volume of hydrogen which can be expected per mass fraction of metal, Al and Mg offer good possibilities in metal hydrolysis. Since these metals hardly react with water, however, a catalyst is used to accelerate the Mg-Al hydrolysis process. Experiments show that a mixture of Mg and Al reacts strongly with water in the presence of CO3O4, MoO3, and Cl-ions; with an optimum combination of all the participants in the reaction, the H2 yield can amount to 100%. Various methods are discussed for constructing a hydrogen generator using this new method of metal hydrolysis. A hydrogen generator plant is described, in which pressed powder pellets are used. An aluminum-magnesium-cobalt oxide powder mixture is introduced into the reactor in the form of cylindrical pellets, which are pulverized in the reactor chamber. The powder falls into the salt water in the reactor and is converted. The hydrogen produced has a purity potentially greater than 99.9%.

  16. 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

  17. 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 >.

  18. A thermokinetic model for Mg-Si couple formation in Al-Mg-Si alloys

    NASA Astrophysics Data System (ADS)

    Svoboda, J.; Shan, Y. V.; Kozeschnik, E.; Fischer, F. D.

    2016-03-01

    Mg-Si couples formed from atomic Mg and Si represent the first step in Mg-Si cluster formation in a dilute Al-Mg-Si system. Based on the thermodynamic extremal principle, a kinetic model for Mg-Si couple formation is developed. The model utilizes the trapping concept for the calculation of Gibbs energy of the non-equilibrium system and provides a generalized (multiplicative) form of the Oriani equation for description of the equilibrium state. The dissipation in the system accounts for diffusion of both Mg and Si atoms in the lattice. The model is compared with the classical Lidiard and Howard equilibrium theory. Some demonstrative examples are presented. Finally the model is applied to an experimentally studied system. Good quantitative agreement with quenching experiments is obtained, if, simultaneously, the impact of excess quenched-in vacancies and their gradual annihilation in the system, which has been already treated in a previous paper, are accounted for. The model is generally applicable for any couple (and pair) formation.

  19. MgAl2O4(001) based magnetic tunnel junctions made by direct sputtering of a sintered spinel target

    NASA Astrophysics Data System (ADS)

    Belmoubarik, Mohamed; Sukegawa, Hiroaki; Ohkubo, Tadakatsu; Mitani, Seiji; Hono, Kazuhiro

    2016-03-01

    We developed a fabrication process of an epitaxial MgAl2O4 barrier for magnetic tunnel junctions (MTJs) using a direct sputtering method from an MgAl2O4 spinel sintered target. Annealing the sputter-deposited MgAl2O4 layer sandwiched between Fe electrodes led to the formation of a (001)-oriented cation-disorder spinel with atomically sharp interfaces and lattice-matching with the Fe electrodes. A large tunnel magnetoresistance ratio up to 245% at 297 K (436% at 3 K) was achieved in the Fe/MgAl2O4/Fe(001) MTJ as well as an excellent bias voltage dependence. These results indicate that the direct sputtering is an alternative method for the realization of high performance MTJs with a spinel-based tunnel barrier.

  20. Analytical electron microscopy of precipitates in ion-implanted MgAl{sub 2}O{sub 4} spinel

    SciTech Connect

    Evans, N.D.; Zinkle, S.J.; Bentley, J.

    1994-12-31

    Magnesium aluminate spinel (MgAl{sub 2}O{sub 4}) is being considered as an insulator material within proposed fusion reactors where considerable radiation fields are anticipated. Analytical electron microscopy (AEM) has been used to investigate precipitates within MgAl{sub 2}O{sub 4} spinel following implantation of Al{sup +}, Mg{sup +}, or Fe{sup 2+} ions. Combined diffraction experiments, energy dispersive X-ray spectrometry (EDS), electron energy-loss spectrometry (EELS), and energy-filtered imaging were employed to identify and characterize precipitates observed in the implanted ion region. Diffraction studies suggested these are metallic aluminum colloids, although EELS and energy-filtered images revealed this to be the case only for the Al{sup +} and Mg{sup +} implantations, and not for Fe{sup 2+} ion implantations. Multiple-least-squares (MLS) fitting of EELS spectra was employed to quantify the volume fraction of metallic aluminum when present in the implanted ion region. Energy-filtered images of the implanted ion region clearly show the colloid distribution in the Al{sup +} and Mg{sup +} implanted spinel. Energy-filtered images from the Fe {sup 2+} ion implanted spinel indicate that the features visible in diffraction contrast cannot be associated with either metallic aluminum or iron-rich precipitates.

  1. Electronic structure and magnetic properties of LiMn{sub 1.5}M{sub 0.5}O{sub 4} (M=Al, Mg, Ni, Fe) and LiMn{sub 2}O{sub 4}/TiO{sub 2} nanocrystalline electrode materials

    SciTech Connect

    Talik, E.; Lipińska, L.; Zajdel, P.; Załóg, A.; Michalska, M.; Guzik, A.

    2013-10-15

    The process of sol–gel synthesis was applied to obtain LiMn{sub 1.5}M{sub 0.5}O{sub 4} (M=Al, Mg, Ni, Fe) and LiMn{sub 2}O{sub 4}/TiO{sub 2} nanopowders. The samples were characterized by following methods: X-ray diffraction (XRD), scanning electron microscopy (SEM/EDX), X-ray photoelectron spectroscopy (XPS) and SQUID magnetometry. XPS was used to examine the chemical composition and oxidation state of manganese, in particular the Mn{sup 3+}/Mn{sup 4+} ratio from the deconvolution of the complex Mn3p lines. The size of the grains and crystallites were independently obtained from SEM images and XRD patterns, respectively. In all the cases a critical interplay of electronic (Mn{sup 3+}/Mn{sup 4+} ratio), structural (unit cell volume) and magnetic properties was observed depending on the synthesis process. - Graphical abstract: SEM image of Li{sub 0.79}Ni{sub 0.41}Mn{sub 1.35}O{sub 4.45} sample. Display Omitted - Highlights: • LiMn{sub 1.5}M{sub 0.5}O{sub 4} (M=Al, Mg, Ni, Fe) and LiMn{sub 2}O{sub 4}/TiO{sub 2} obtained by sol–gel method. • XRD method was used to determine the crystal structure. • SEM/EDX imaging have been done. • XPS electronic structure was examined and discussed. • Experimental effective magnetic moment and the calculated one were compared.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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.

  3. 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.

  4. 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

  5. Magnetic Tunnel Junctions with MgO/Al O Composite Barriers

    NASA Astrophysics Data System (ADS)

    Li, Fei-Fei; Jiang, Li-Xian; Sharif, Rehana; Zhang, Xie-Qun; Feng, Yu-Qing; Han, Xiu-Feng

    2005-08-01

    Magnetic tunnel junctions (MTJs) with structures of Ta(5 nm)/Cu(30 nm)/Ta(5 nm)/Ni79Fe21(5 nm)/Ir22Mn78 (12 nm)/Co62Fe20B18(4 nm)/MgO(d)/Al(0.8 nm)-oxide/Co62Fe20B18(6 nm)/Cu(30 nm)/Ta(5 nm) on a thermally oxidized Si wafer substrate were fabricated by magnetron sputtering and photolithographic patterning method. The tunnel magnetoresistance (TMR) and the bias dependence of TMR at room temperature for the MTJs with different thickness d of MgO are investigated. TMR values of over 50% as high as those of the MTJs with pure Al-O barrier and the TMR-voltage curve asymmetries, which vary with the increase of d, are observed in the MTJs with hybrid barriers after annealing at 265°C for an hour. The dependences of TMR, resistance and coercivity of the MTJs with composite barriers on temperature are also investigated.

  6. Ru Catalyst-Induced Perpendicular Magnetic Anisotropy in MgO/CoFeB/Ta/MgO Multilayered Films.

    PubMed

    Liu, Yiwei; Zhang, Jingyan; Wang, Shouguo; Jiang, Shaolong; Liu, Qianqian; Li, Xujing; Wu, Zhenglong; Yu, Guanghua

    2015-12-01

    The high oxygen storage/release capability of the catalyst Ru is used to manipulate the interfacial electronic structure in spintronic materials to obtain perpendicular magnetic anisotropy (PMA). Insertion of an ultrathin Ru layer between the CoFeB and Ta layers in MgO/CoFeB/Ta/MgO films effectively induces PMA without annealing. Ru plays a catalytic role in Fe-O-Ta bonding and isolation at the metal-oxide interface to achieve moderate interface oxidation. In contrast, PMA cannot be obtained in the sample with a Mg insertion layer or without an insertion layer because of the lack of a catalyst. Our work would provide a new approach toward catalyst-induced PMA for future CoFeB-based spintronic device applications. PMID:26565747

  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. Parasitic capacitance of FeCo/MgO/FeCo magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Abedi Ravan, B.; Shokri, A. A.

    2012-04-01

    In this work, we report a theoretical investigation of parasitic capacitance in FeCo/MgO/FeCo magnetic tunnel junctions (MTJs). The electronic structures needed for accomplishment of this work are computed within the density functional theory using the full-potential linearized augmented plane-wave method (FLAPW) as implemented in Wien2k. Fixed-spin-moment (FSM) calculations are used to simulate the interfacial effects on the electronic structure of the electrodes. It is discussed that the charge screening at surfaces of the electrodes alters their local electric permittivities. The relative electric permittivities of the electrodes are calculated and their effects on the overall capacitance of the MTJ are estimated. Finally, capacitive properties of the MTJ are investigated and it is resulted that its capacitance, especially for the Co-ending electrodes, is not considerably dependent on an externally applied magnetic field.

  9. Spin injection studies on thin film Fe/MgO/Si tunneling devices

    NASA Astrophysics Data System (ADS)

    Beardsley, Jonas; Pu, Yong; Swartz, Adrian; Bhallamudi, Vidya; Kawakami, Roland; Johnston-Halperin, Ezekiel; Hammel, Chris; Pelz, Jon

    2011-03-01

    We report progress on the injection of spin polarized electrons into 35 nm thick Si films, using Fe/MgO injector/tunnel barrier structures grown by molecular beam epitaxy on SIMOX silicon-on-insulator substrates. The device requires heavy top-surface n-type doping of the Si film to produce a suitable tunnel barrier, accomplished by diffusion from a spin-on phosphorous-doped glass. Measurements indicate a roughly exponential doping profile with 7E20 per cubic cm at the top surface and a 2 nm decay length. Three terminal measurements showed evidence of spin injection similar to reports of Jansen et al., while injection with a thinner MgO barrier shows more complicated behavior. On-going measurements and modeling will be discussed.

  10. Metastability in the MgAl2O4-Al2O3 System

    DOE PAGESBeta

    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. 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.

  12. 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.

  13. 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.

  14. Electric and thermal spin torque across disordered FeCo/MgO/FeCo magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Wang, Shi-Zhuo; Xia, Ke

    2016-05-01

    We report on a first principles study of the spin transfer torque (STT) induced by electric voltages across and temperature gradients through Fe0.5Co0.5/MgO /Fe0.5Co0.5 (001) magnetic tunnel junctions (MTJs). A small amount of interfacial oxygen vacancies (OVs) has demonstrated considerable effects on the bias-dependent STT, enabling the "threshold voltage" for in-plane STT to be optimized to 0.2 V, and one sample with an asymmetric OV distribution reproduced the experimental measurements. The spin torque efficiency increases with the MgO barrier thickness until it reaches a constant value, while interfacial OVs tend to reduce the efficiency when compared with that of the perfect junction. The thermal spin torque (TST) is also affected greatly by imperfections at the interface, leading to enhancements in FeCo/MgO/FeCo junctions, whereas a weakening effect is found in Fe/MgO/Fe junctions. The TST magnitude in FeCo/MgO/FeCo MTJs is typically smaller than that of a similar MTJ with Fe electrodes.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Thermal expansion study of a "Direct Chill Casting" AlMgSi alloy

    NASA Astrophysics Data System (ADS)

    Guemini, R.; Boubertakh, A.; Hamamda, S.

    2001-03-01

    This work is concerned with the study of thermal expansion coefficient of Al-0.59 wt.% Mg- 0.88 wt.% Si-0.30 wt.% Fe-0.44 wt.% Mn alloy. The presence of the anisotropy was concluded on the basis of the thermal expansion coefficient α(T) which depends up on the two directions: radial (1) and axial (2). However α(T) measured along the axial direction (2) appeared to be inferior to the measured one along the radial direction (1) in both as-cast and homogenised alloy.

  2. High-pressure transitions in MgAl{sub 2}O{sub 4} and a new high-pressure phase of Mg{sub 2}Al{sub 2}O{sub 5}

    SciTech Connect

    Enomoto, A.; Kojitani, H.; Akaogi, M. Miura, H.; Yusa, H.

    2009-02-15

    Phase transitions in MgAl{sub 2}O{sub 4} were examined at 21-27 GPa and 1400-2500 deg. C using a multianvil apparatus. A mixture of MgO and Al{sub 2}O{sub 3} corundum that are high-pressure dissociation products of MgAl{sub 2}O{sub 4} spinel combines into calcium-ferrite type MgAl{sub 2}O{sub 4} at 26-27 GPa and 1400-2000 deg. C. At temperature above 2000 deg. C at pressure below 25.5 GPa, a mixture of Al{sub 2}O{sub 3} corundum and a new phase with Mg{sub 2}Al{sub 2}O{sub 5} composition is stable. The transition boundary between the two fields has a strongly negative pressure-temperature slope. Structure analysis and Rietveld refinement on the basis of the powder X-ray diffraction profile of the Mg{sub 2}Al{sub 2}O{sub 5} phase indicated that the phase represented a new structure type with orthorhombic symmetry (Pbam), and the lattice parameters were determined as a=9.3710(6) A, b=12.1952(6) A, c=2.7916(2) A, V=319.03(3) A{sup 3}, Z=4. The structure consists of edge-sharing and corner-sharing (Mg, Al)O{sub 6} octahedra, and contains chains of edge-sharing octahedra running along the c-axis. A part of Mg atoms are accommodated in six-coordinated trigonal prism sites in tunnels surrounded by the chains of edge-sharing (Mg, Al)O{sub 6} octahedra. The structure is related with that of ludwigite (Mg, Fe{sup 2+}){sub 2}(Fe{sup 3+}, Al)(BO{sub 3})O{sub 2}. The molar volume of the Mg{sub 2}Al{sub 2}O{sub 5} phase is smaller by 0.18% than sum of molar volumes of 2MgO and Al{sub 2}O{sub 3} corundum. High-pressure dissociation to the mixture of corundum-type phase and the phase with ludwigite-related structure has been found only in MgAl{sub 2}O{sub 4} among various A{sup 2+}B{sup 3+}{sub 2}O{sub 4} compounds. - Graphical abstract: MgAl{sub 2}O{sub 4} dissociates into a mixture of Al{sub 2}O{sub 3} corundum and a new high-pressure phase of Mg{sub 2}Al{sub 2}O{sub 5} at high pressures and temperatures. The Mg{sub 2}Al{sub 2}O{sub 5} phase represents a new structure type with

  3. The Charpy impact behavior of Fe{sub 3}Al and Fe{sub 3}Al-20 at % Mn alloys

    SciTech Connect

    Liu, J.N.; Yan, W.; Ma, J.L.; Wu, K.H.

    1997-12-31

    A series of experiments were conducted to investigate the impact fracture behavior of Fe{sub 3}Al and Fe{sub 3}Al-20 Mn alloys. The results of this study indicated that: (i) The addition of Mn introduces an ordered L1{sub 2}-type phase in the Fe{sub 3}Al-based alloys. On the other hand, the addition of Mn decreases the order parameter of the DO{sub 3} {alpha} phase. (ii) The total-impact energy of an Fe{sub 3}Al alloy increases with the temperature at the low-temperature range (<600 C), then drops around 700 C, and finally increases again as the temperature further elevates. (iii) The trend of the variation of the impact energy of Fe{sub 3}Al-20 at % Mn alloy with temperature is the same as that of the Fe{sub 3}Al alloy. (iv) And the addition of Mn significantly improves the impact energy of the Fe{sub 3}Al-based alloy, and changes the variation of the crack-growth energy with the testing temperature when the temperature is above 700 C.

  4. 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.

  5. Growth and holographic storage properties of Mg:Fe:LiTaO3 crystal

    NASA Astrophysics Data System (ADS)

    Zhao, Yequan; Fang, Shuangquan; Xu, Wusheng; Xu, Yuheng

    2003-04-01

    Mg:Fe:LiTaO3 crystals were first grown by Czochralski method, and Fe:LiTaO3 crystals, Fe:LiNbO3 and Mg:Fe:LiNbO3 crystals were also grown at the same time. The holographic storage properties of these crystals, such as the exponential gain coefficient, the diffraction efficiency and the response time, were measured by the two-wave coupling method. It was found that the response speed of Mg:Fe:LiTaO3 crystal was five times faster than that of Fe:LiTaO3. The light scattering resistance ability was also measured, and that of Mg:Fe:LiTaO3 crystal was two orders of magnitude higher than that of Fe:LiTaO3 as well as higher than that of Mg:Fe:LiNbO3. The enhancement mechanism of the photorefractive properties for Mg:Fe:LiTaO3 crystal was discussed for the first time.

  6. Microstructure Evolution of Atomized Al-0.61 wt pct Fe and Al-1.90 wt pct Fe Alloys

    NASA Astrophysics Data System (ADS)

    Chen, Jian; Dahlborg, Ulf; Bao, Cui Min; Calvo-Dahlborg, Monique; Henein, Hani

    2011-06-01

    The microstructure evolution of impulse atomized powders of Al-0.61 wt pct and Al-1.90 wt pct Fe compositions have been investigated with a scanning electron microscope, transmission electron microscope, neutron diffraction, and backscattering electron diffraction (EBSD). Both hypoeutectic and hypereutectic compositions demonstrated similar macrostructure ( i.e., primary α-Al dendrites/cells with eutectic Al-Fe intermetallics decorated at the dendritic/cellular walls). Selected area electron diffraction (SAED) analysis and SAED pattern simulation identified the eutectic Al-Fe intermetallic as AlmFe ( m = 4.0-4.4). This is verified by neutron diffraction analysis. Cubic texture was observed by EBSD on the droplets with dendritic growth direction close to <111>. The possible reasons are discussed.

  7. Thermal Properties in the MgAl2O4-Al2O3 System

    SciTech Connect

    Wilkerson, Dr. Kelley R.; Smith, Jeffrey D; Hemrick, James Gordon

    2013-01-01

    Compositional effects on the thermal diffusivity in the MgAl2O4-Al2O3 system were studied. The lowest thermal diffusivity, 0.0258 +/-5% cm/s, was measured between 79.8 and 83.9 wt% Al2O3 quenched from various temperatures between 1500 and 1700C. All of the chemistries in this range extend past the solvus, but still form a singe super-saturated spinel solid solution, regardless of quenching tempeature. A super-saturated metastable solid solution region was observed at 1500, 1600, and 1700C extending to 83.9, 85.2, and 87.1 wt% Al2O3, respectively. Beyond 83.9% Al2O3 a significant increase in thermal diffusivity, 11.7%, was observed and its attributed to precipiation of Al2O3 through spinodal decomposition.

  8. 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

  9. 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

    2016-06-01

    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.

  10. 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

  11. New antimony substituted Mg-Al layered double hydroxides.

    PubMed

    Kim, Jin A; Hwang, Seong-Ju; Choy, Jin-Ho

    2008-10-01

    No antimony hydroxide has been previously reported not only in solid state but also in aqueous solution, surely due to the fact that the formation of antimony oxide, Sb2O3, is thermodynamically more favorable than that of the hydroxide phase, Sb(OH)3. According to the pH dependent solubility diagram of Sb2O3, antimony (III) hydroxide may not exist as a definite compound but be proposed as a hydrated monomeric molecular species, Sb(OH)3(aq), which is in equilibrium with Sb2O3, under a condition of very small ionic strength. This is probably the reason why no Sb(3+)-containing layered double hydroxide, LDH, has been reported as yet. In the present study, an attempt has been made to prepare new Sb(3+)-LDH by substituting the Al3+ in octahedral site partially with Sb3+ up to approximately 10%. From the X-ray diffraction analysis, we found that the lattice constants (a = 3.075 angstroms, c = 23.788 angstroms) of the pristine, Mg-Al LDH, increased gradually upto those (a = 3.087 angstroms, c = 24.167 angstroms) of Sb-LDH (8%-substituted). Beyond 10%, the Sb substitution does not lead to any further increases of lattice constants but the impurity Sb2O3 phase is formed. It is, therefore, concluded that the solubility limit of Sb3+ in LDH would be around 10%. In addition, we were able to determine the chemical formula of Sb-substituted LDHs as follows, Mg4Al(1-x)Sb(x)OH10(CO3)(1/2) x H2O (x = 0 approximately 0.08) on the basis of energy dispersive X-ray spectroscopy. PMID:19198414

  12. Combinatorial pulsed laser deposition of Fe/MgO granular multilayers

    NASA Astrophysics Data System (ADS)

    García-García, A.; Pardo, J. A.; Navarro, E.; Štrichovanec, P.; Vovk, A.; Morellón, L.; Algarabel, P. A.; Ibarra, M. R.

    2012-06-01

    Combinatorial pulsed laser deposition (PLD) makes use of the angular spread of laser-ablated material to prepare thin films with lateral compositional gradient. In this paper we have used combinatorial PLD to grow discontinuous Fe/MgO multilayers by alternate ablation from two separate Fe and MgO targets. Films of composition [Fe( t Fe)/MgO( t MgO)]15 were deposited on glass substrates. The thickness of Fe and MgO were varied in the vicinity of critical values determined in previous studies to maximize the tunneling magnetoresistance (TMR) in the current-in-plane configuration. Optimized multilayers show a substantial improvement of both TMR and field sensitivity at room temperature.

  13. 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.

  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. 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.

  16. 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

  17. 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.

  18. 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.

  19. Solubility of Fe(III) and Al in AMD by modelling and experimtn

    SciTech Connect

    Mitchell, K.G.; Wildeman, T.R.

    1995-12-01

    Studies of Fe(III) and Al species in acid mine drainage (AMD) alone and in contact with limestone were conducted by MINTEQA2 and by experiments. Using Fe(OH){sub 3} as the primary species and the standard values for MINTEQ, Fe(III) precipitates at pH 2.90 when the concentration is 453 mg/L. Al precipitates at a pH of 4.00 when the concentration is 108 mg/L. Experiments found that over 90 % of Fe(III) and 45 % of Al were precipitated at these pH`s. Experimental verification of Fe(III) concentrations at pH`s from 2.90 to 4.0 found that modelling agreed with experiment when ferrihydrite is the primary solid and the log Ksp is -38.9. For Al, gibbsite would be the primary solid and log Ksp is -34.1. For AMD in contact with CaCO{sub 3} when CO{sub 2} is conserved, final alkalinity is higher when mineral acidity is higher even though pH of the final solution is lower. This modelling result was confirmed by experiment. Higher mineral acidity causes generation of more CO{sub 2} that reacts with CaCO{sub 3} to generate more dissolved HCO{sub 3-}.

  20. 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).

  1. Measuring Ages and Elemental Abundances from Unresolved Stellar Populations: Fe, Mg, C, N, and Ca

    NASA Astrophysics Data System (ADS)

    Graves, Genevieve J.; Schiavon, Ricardo P.

    2008-08-01

    We present a method for determining mean light-weighted ages and abundances of Fe, Mg, C, N, and Ca from medium-resolution spectroscopy of unresolved stellar populations. The method is implemented in a publicly available code called EZ_Ages. The method and error estimation are described, and the results tested for accuracy and consistency, by application to integrated spectra of well-known Galactic globular and open clusters. Ages and abundances from integrated light analysis agree with studies of resolved stars to within ±0.1 dex for most clusters, and to within ±0.2 dex for nearly all cases. The results are robust to the choice of Lick indices used in the fitting to within ±0.1 dex, except for a few systematic deviations that are clearly categorized. The realism of our error estimates is checked through comparison with detailed Monte Carlo simulations. Finally, we apply EZ_Ages to the sample of galaxies presented in Thomas et al. (2005) and compare our derived values of age, [Fe/H], and [α/Fe] to their analysis. We find that [α/Fe] is very consistent between the two analyses, that ages are consistent for old (age > 10 Gyr) populations but show modest systematic differences at younger ages, and that [Fe/H] is fairly consistent, with small systematic differences related to the age systematics. Overall, EZ_Ages provides accurate estimates of fundamental parameters from medium-resolution spectra of unresolved stellar populations in the old and intermediate-age regime, for the first time allowing quantitative estimates of the abundances of C, N, and Ca in these unresolved systems.

  2. 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.

  3. 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

  4. Preparation and characterization of thin films of MgO, Al2O3 and MgAl2O4 by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Huang, Ron; Kitai, Adrian H.

    1993-02-01

    MgO, Al2O3 and MgAl2O4 thin films were deposited on silicon substrates at various temperatures by the atomic layer deposition (ALD) method using bis(cyclopentadienyl)magnesium, triethylaluminum, and H2O and were characterized systematically. High-quality polycrystalline MgO films were deposited for a substrate temperature above 500°C, and amorphous thin films were deposited around 400°C. The deposited Al2O3 and MgAl2O4 thin films were characterized as amorphous in structure. Applicability of ALD to complex oxides is discussed.

  5. Magnetization study of the ultra-hard material MgAlB 14

    NASA Astrophysics Data System (ADS)

    Hill, J. M.; Johnston, D. C.; Cook, B. A.; Harringa, J. L.; Russell, A. M.

    2003-09-01

    Magnetic susceptibility χ versus temperature T, magnetization M versus T, and isothermal M versus magnetic field H studies of the ultra-hard material MgAlB 14 were carried out in search of superconductivity or ferromagnetism in this compound. Two types of samples were synthesized: (1) powder and (2) chemically substituted and unsubstituted hot pressed pellets prepared from mechanically alloyed powders. χ( T) measurements on a powder sample revealed temperature-independent diamagnetism with a Curie-Weiss impurity concentration equivalent to ˜1 mol% of spin- {1}/{2} ions. In contrast, M( T) and M( H) data on the hot pressed samples, both substituted and unsubstituted, showed evidence of ferromagnetic transitions above ˜330 K. Scanning electron microscopy and Auger microprobe analysis of the hot pressed samples indicated that both substituted and unsubstituted samples contained significant concentrations of Fe impurities. We conclude that pure MgAlB 14 is neither a superconductor nor a ferromagnet above 1.8 K and exhibits temperature-independent diamagnetism from 1.8 K up to room temperature. The ferromagnetism observed in the hot pressed samples is likely due to Fe impurities abraded from the stainless steel mills used to mix the starting materials prior to hot pressing the samples.

  6. 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)

  7. 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.

  8. 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.

  9. An Assessment of the Al- Fe- N System

    NASA Astrophysics Data System (ADS)

    Hillert, Mats; Jonsson, Stefan

    1992-11-01

    The thermodynamic properties of the Al-Fe-N system are assessed, taking various types of information into account. For solid AIN, a description very similar to that given by JANAF is found to yield reasonable predictions for the solubility of A1N in face-centered cubic (fcc) Fe and in liquid Fe. An ionic two-sublattice model is applied to the liquid phase, containing two N species, N-3 and N0 The melting point of A1N is taken as 3068 K, and a required gas pressure of 9.75 bar is predicted. A sublimation point of 2690 K at 1 bar is also predicted. A plot of the liquidus surfaces in the Fe-rich end of the Al-Fe-N system is presented.

  10. 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.

  11. Mössbauer and SEM study of Fe Al film

    NASA Astrophysics Data System (ADS)

    Sebastian, Varkey; Sharma, Ram Kripal; Lakshmi, N.; Venugopalan, K.

    2006-04-01

    Fe Al alloy with Fe/Al ratio of 3:1 was first prepared by argon arc melting. It was subsequently coated on glass slide and cellophane tape using an electron beam gun system to have a thickness of 2,000 Å. X-ray diffraction spectrum of the coated sample indicates a definite texture for the film with a preferential growth along the Fe(110) plane. SEM micrographs of the film showed the presence of nano islands of nearly 3 × 1012/m2 surface density. Composition of different parts of the film was determined using EDAX. Room temperature Fe-57 Mössbauer spectrum of coated sample showed the presence a quadrupole doublet with a splitting of 0.46 mm/s, which is typical of Al-rich iron compounds. MOKE study shows an in-plane magnetic moment.

  12. 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

  13. 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.

  14. 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

  15. 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

  16. 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.

  17. Spin-dependent tunneling spectroscopy for interface characterization of epitaxial Fe/MgO/Fe magnetic tunnel junctions

    SciTech Connect

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

    2010-01-01

    Low-voltage spin-dependent tunneling spectroscopy of an epitaxial Fe/MgO/Fe magnetic tunnel junction is measured and compared to first-principles calculation of the tunneling conductance. The measured dynamic conductance ($dI/dV$) in the parallel configuration shows distinct asymmetric features as a function of the bias voltage $V$. The peaks are independent of barrier thickness, magnetic field, and temperature. From the first-principles calculation, we identify the positive and negative bias spectra corresponding to different types of Fe/MgO interfaces. Tunneling spectroscopy thus can be used as a powerful tool for interface characterization.

  18. 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.

  19. 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

  20. Point defects in (Mg,Fe)O at high pressures: where does hydrogen dominate over ferric iron?

    NASA Astrophysics Data System (ADS)

    Otsuka, K.; Karato, S.

    2007-12-01

    The point defects play an important role in transport processes of minerals including diffusion, electrical conduction and plastic deformation. Point defects caused by ferric iron and/or hydrogen (proton) are dominant defects in most of the iron-bearing minerals including olivine and (Mg,Fe)O. In many upper-mantle minerals such as olivine, the concentration of ferric iron is much smaller than that of hydrogen, and therefore the small amount of hydrogen changes their transport properties dramatically. However, the situation is very different for lower- mantle minerals such as (Mg,Fe)O. In this presentation, we will review the available experimental data on point defects in (Mg,Fe)O and discuss the relative importance of ferric iron and hydrogen at high pressures based on atomic models. The existing low-pressure data indicate that the maximum solubility of ferric iron in (Mg,Fe)O is on the order of 0.1 (atomic fraction in the total iron), which is much higher than that of hydrogen. However, experimental studies by Bolfan-Casanova et al (2002, 2006) indicate that the solubility of ferric iron decreases while that of hydrogen increases with pressure. This suggests that the dominant impurity to generate point defects in (Mg,Fe)O may change from ferric iron to hydrogen at high pressure. Therefore it is important to quantify the pressure dependence of the solubility of ferric iron and hydrogen. We have explored two models of ferric iron- related defects and found that the existing experimental data suggest that ferric iron may occur at two lattice sites: the tetrahedral site as interstitial atoms as well as the octahedral site. The pressure dependence of the solubility of hydrogen in (Mg,Fe)O are also estimated based on the experimental data and defect models. The cross-over of defect solubility likely occurs in the lower mantle, but the exact depth is poorly constrained because of large uncertainties in the hydrogen solubility and the mechanisms of hydrogen dissolution

  1. Electric field effect on a double MgO CoFeB-based free layer

    NASA Astrophysics Data System (ADS)

    Huang, Jiancheng; Sim, Cheow Hin; Naik, Vinayak Bharat; Tran, Michael; Lim, Sze Ter; Huang, Aihong; Yap, Qi Jia; Han, Guchang

    2016-03-01

    We study the electric field (EF) effect on MgO/CoFeB/Ta/CoFeB/MgO free layers by varying the thickness of the top MgO layer. The two CoFeB/MgO interfaces oppose the change in magnetic anisotropy from each other and this can be understood by considering the voltage drop as well as the efficiency of the anisotropy modulation from both interfaces. These results are proven by monitoring both coercivity and anisotropy field as a function of the applied EF. From the fit to the model, we show that the bottom CoFeB/MgO interface has a higher EF efficiency than the top interface.

  2. High-pressure stability, structure and compressibility of Cmcm -MgAl2O4: an ab initio study

    NASA Astrophysics Data System (ADS)

    Catti, M.

    Quantum-mechanical solid-state calculations have been performed on the highest-pressure polymorph of magnesium aluminate (CaTi2O4-type structure, Cmcm space group), as well as on the low-pressure (Fd3m) spinel phase and on MgO and Al2O3. An ab initio all-electron periodic scheme with localized basis functions (Gaussian-type atomic orbitals) has been used, employing density-functional-theory Hamiltonians based on LDA and B3LYP functionals. Least-enthalpy structure optimizations in the pressure range 0 to 60 GPa have allowed us to predict: (1) the full crystal structure, the pV equation of state and the compressibility of Cmcm-MgAl2O4 as a function of pressure; (2) the phase diagram of the MgO-Al2O3-MgAl2O4 system (with exclusion of CaFe2O4-type Pmcn-MgAl2O4), and the equilibrium pressures for the reactions of formation/decomposition of the Fd3m and Cmcm polymorphs of MgAl2O4 from the MgO + Al2O3 assemblage. Cmcm-MgAl2O4 is predicted to form at 39 and 57 GPa by LDA and B3LYP calculations, with K0=248 (K'=3.3) and 222 GPa (K'=3.8), respectively. Results are compared to experimental data, where available, and the performance of different DFT functionals is discussed.

  3. 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.

  4. 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

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

    PubMed

    Gallagher, James R; Boldrin, Paul; Combes, Gary B; Ozkaya, Don; Enache, Dan I; Ellis, Peter R; Kelly, Gordon; Claridge, John B; Rosseinsky, Matthew J

    2016-02-28

    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

  6. 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

  7. Solidification Pathways of Alloys in the Mg-Rich Corner of the Mg-Al-Ba Ternary System

    NASA Astrophysics Data System (ADS)

    Bryan, Zachary L.; Hooper, Ryan J.; Henderson, Hunter B.; Manuel, Michele V.

    2015-04-01

    An experimental investigation of the solidification reactions and microstructures of alloys in the Mg-rich corner of the Mg-Al-Ba ternary system has been conducted. Four distinct exothermic reactions involving the formation of α-Mg, Mg17Ba2, Mg17Al12, and a fourth phase designated as τ were observed and their onset temperatures were recorded as functions of composition. Using compositional and microstructural analysis, the Mg17Ba2 intermetallic was found to have significant solubility of Al, up to 20 at. pct. The solidification pathways of the investigated alloys involved both a Class I and Class II equilibrium reaction. A flow block diagram that outlines the observed solidification reactions is presented and discussed in reference to cast microstructures.

  8. 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.

  9. 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.

  10. 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.

  11. Tunable electronic structures of p-type Mg doping in AlN nanosheet

    SciTech Connect

    Peng, Yuting; Xia, Congxin Zhang, Heng; Wang, Tianxing; Wei, Shuyi; Jia, Yu

    2014-07-28

    The p-type impurity properties are investigated in the Mg-doped AlN nanosheet by means of first-principles calculations. Numerical results show that the transition energy levels reduce monotonously with the increase in Mg doping concentration in the Mg-doped AlN nanosheet systems, and are lower than that of the Mg-doped bulk AlN case for the cases with larger doping concentration. Moreover, Mg substituting Al atom is energy favorably under N-rich growth experimental conditions. These results are new and interesting to further improve p-type doping efficiency in the AlN nanostructures.

  12. Study on biodegradation of the second phase Mg17Al12 in Mg-Al-Zn alloys: in vitro experiment and thermodynamic calculation.

    PubMed

    Liu, Chen; Yang, Huazhe; Wan, Peng; Wang, Kehong; Tan, Lili; Yang, Ke

    2014-02-01

    The in vitro biodegradation behavior of Mg17Al12 as a second phase in Mg-Al-Zn alloys was investigated via electrochemical measurement and immersion test. The Hank's solutions with neutral and acidic pH values were adopted as electrolytes to simulate the in vivo environment during normal and inflammatory response process. Furthermore, the local orbital density functional theory approach was employed to study the thermodynamical stability of Mg17Al12 phase. All the results proved the occurrence of pitting corrosion process with crackings for Mg17Al12 phase in Hank's solution, but with a much lower degradation rate compared with both AZ31 alloy and pure magnesium. Furthermore, a preliminary explanation on the biodegradation behaviors of Mg17Al12 phase was proposed. PMID:24411344

  13. 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.

  14. Solubility of Fe(III) Al in AMD by modelling and experiment

    SciTech Connect

    Mitchell, K.G.; Wildeman, T.R.

    1996-12-31

    Studies of Fe(III) and Al species in acid mine drainage (AMD) alone and in contact with limestone were conducted by MINTEQA2 modelling and by experiments. The objectives of these studies were to: (1) determine at what pH Fe(III) and Al would be in solution in AMD such that the water would be harmful to an anoxic limestone drain (ALD), and (2) evaluate the theoretical limits to the amount of alkalinity that could be generated by an ALD. Using Fe(OH){sub 3} as the primary species and the standard values for MINTEQA2, Fe(III) precipitates at pH 2.90 when the concentration is over 453 mg/L. Al precipitates at a pH of 4.00 when the concentration is over 108 mg/L. Experiments found that over 90 % of Fe(III) and 45% of Al were precipitated at these pH`s. Experimental verification of Fe(III) concentrations of pH`s from 2.90 to 4.0 found that modelling agreed with experiment when ferrihydrite is the primary solid and the log Ksp (solubility product) is -38.9. For Al, gibbsite would be the primary solid and log Ksp is -34.1. For AMD in contact with CaCO{sub 3} when CO{sub 2} is conserved, final alkalinity is higher when mineral acidity is higher even though pH of the final solution is lower. This modelling result was confirmed by experiment. Higher mineral acidity causes generation of more CO{sub 2} that reacts with CaCO{sub 3} to generate more dissolved HCO{sub -3}.

  15. 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

  16. Growth and optical properties of Mg, Fe Co-doped LiTaO3 crystal

    NASA Astrophysics Data System (ADS)

    Fang, Shuangquan; Ma, Decai; Zhang, Tao; Ling, Furi; Wang, Biao

    2006-02-01

    Mg, Fe double-doped LiTaO3 and LiNbO3 crystals have been grown by Czochralski method. The optical properties were measured by two-beam coupling experiments and transmitted facula distortion method. The results showed that the photorefractive response speed of Mg:Fe:LiTaO3 was about three times faster than that of Fe:LiTaO3, whereas the photo-damage resistance was two orders of magnitude higher than that of Fe:LiTaO3. In this paper, site occupation mechanism of impurities was also discussed to explain the high photo-damage resistance and fast response speed in Mg:Fe:LiTaO3 crystal.

  17. Effect of cation substitution at the B site on the oxygen semi-permeation flux in La0.5Ba0.5Fe0.7B0.3O3-δ dense perovskite membranes with B = Al, Co, Cu, Mg, Mn, Ni, Sn, Ti and Zn (part II)

    NASA Astrophysics Data System (ADS)

    Reichmann, M.; Geffroy, P.-M.; Fouletier, J.; Richet, N.; Del Gallo, P.; Chartier, T.

    2015-03-01

    The aim of this paper is to provide insight into the effect of cation substitution at the B site on the oxygen semi-permeation performances. Particular attention is given here to identify the impact of cation substitution at the B site on oxygen diffusion and oxygen surface-exchange kinetics in the La0.5Ba0.5Fe0.7B0.3O3-δ perovskite membrane series with B = Al, Co, Cu, Mg, Mn, Ni, Sn, Ti and Zn. This study clearly shows that the prediction of the oxygen semi-permeation performances of membrane materials from the nature of cation at the A or B sites in perovskite structure is quite complex. The cation substitution at the B-site has a low impact on the nature of rate-determining step and a significant impact on oxygen semi-permeation performances, contrary to the cation substitution at A-site. Unfortunately, it is not possible to establish a relevant trend about the effect of the nature of cation in the A or B sites in perovskite structure on oxygen diffusion and the oxygen surface-exchange kinetics.

  18. Impact of a Revised 25Mg(p, γ)26Al Reaction Rate on the Operation of the Mg-Al Cycle

    NASA Astrophysics Data System (ADS)

    Straniero, O.; Imbriani, G.; Strieder, F.; Bemmerer, D.; Broggini, C.; Caciolli, A.; Corvisiero, P.; Costantini, H.; Cristallo, S.; DiLeva, A.; Formicola, A.; Elekes, Z.; Fülöp, Zs.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, Gy.; Junker, M.; Lemut, A.; Limata, B.; Marta, M.; Mazzocchi, C.; Menegazzo, R.; Piersanti, L.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Terrasi, F.; Trautvetter, H.-P.

    2013-02-01

    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 25Mg(p, γ)26Al reaction affect the production of radioactive 26Algs 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 25Mg(p, γ)26Algs and the 25Mg(p, γ)26Al m reactions with corresponding uncertainties. In the temperature range 50-150 MK, the new recommended rate of 26Al 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 25Mg(p, γ)26Al m rate, the estimated production of 26Algs 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 26Al budget. Similarly, we show that the asymptotic giant branch (AGB) extra-mixing scenario does not appear able to explain the most extreme values of 26Al/27Al, i.e., >10-2, 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.

  19. Fe:ZnSe and Fe:ZnMgSe lasers pumped by Er:YSGG radiation

    NASA Astrophysics Data System (ADS)

    Jelínková, H.; Doroshenko, M. E.; Jelínek, M.; Å ulc, J.; Němec, M.; Kubeček, V.; Zagoruiko, Y. A.; Kovalenko, N. O.; Gerasimenko, A. S.; Puzikov, V. M.; Komar, V. K.

    2015-02-01

    The aim of the presented work was to design and characterize bulk Fe:ZnSe and Fe:Zn(1-x)Mg(x)Se (Mg content x = 0.19) lasers coherently pumped by electro-optically Q-switched Er:YSGG laser. This laser generated pumping radiation at 2.79 μm with the maximum energy of 50 mJ in 80 ns long pulse with the repetition-rate of 1 Hz. The 25 mm long optical resonator of Fe:ZnSe or Fe:ZnMgSe lasers was formed by a plan dichroic pumping mirror and a concave output coupler (r = 200 mm) with reflectivity 88 % @ 4-5 μm. Both lasers were operated at room temperature. Measured maximum output energy/slope efficiency in respect to the absorbed energy was ~ 3.8 mJ/42 % for the Fe:ZnSe laser and ~ 0.48 mJ/10 % for the Fe:ZnMgSe laser. The generated output pulse duration was 150 - 200 ns in both cases and the output beam spatial profile was approximately gaussian. The Fe:ZnSe and Fe:ZnMgSe lasers output spectra line-width was ~ 200 nm (FWHM) and their maxima were centered at 4.45 μm and 4.8 μm, respectively. The results were compared to pumping the same crystals by a Q-switched Er:YAG laser in similar conditions.

  20. 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.

  1. 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.

  2. The effect of coarse second phase particles on fatigue crack propagation of an Al-Zn-Mg-Cu alloy

    SciTech Connect

    Guerbuez, R.; Alpay, S.P. . Dept. of Metallurgical Engineering)

    1994-06-01

    The objective of this study is to determine the role of the most commonly observed coarse second phase particles; Al[sub 7]Cu[sub 2]Fe, Mg[sub 2]Si and CuAl[sub 2]Mg on the Stage 2 fatigue crack propagation of a 7050 aluminum alloy. The differences in the composition of this alloy when compared to the conventional 7075 alloy are: (1) increased Cu content for additional strengthening during aging and for increasing the temperature range of GP zone stability; (2) replacement of Cr by Zr to reduce quench sensitivity; (3) reduced Fe and Si contents to improve fracture toughness which, however, decreases fatigue crack growth threshold, [Delta]K[sub th], slightly; and (4) increased Zn content for strengthening.

  3. Slip, twinning and transformation in Laves phases. [Ti-TiCr[sub 2]; Fe-ZrFe[sub 2]; Ni-Cu-Mg containing MgNi[sub 2] and MgCu[sub 2

    SciTech Connect

    Allen, S.M.; Livingston, J.D.

    1993-01-26

    Research was concentrated on two-phase Ti-TiCr[sub 2] alloys, two- phase Fe-ZrFe[sub 2] alloys, and two-phase ternary Ni-Cu-Mg alloys containing MgNi[sub 2] and MgCu[sub 2] phases. Work demonstrated that a variety of room-temperature deformation processes are possible in Laves phases. A strain-induced phase transformation from C36[r arrow]C15 structures is one mechanism for plastic deformation in ZrFe[sub 2]. The C15 structure in TiCr[sub 2] deforms by slip and twinning. The microstructure after indentation of specimens containing C36 phases ZrFe[sub 2] and MgNi[sub 2] indicates that a variety of slip systems operate in this form. 8 figs.

  4. 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.

  5. 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.

  6. 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.

  7. The corrosion behavior of Fe-Mn-Al weld metals

    NASA Astrophysics Data System (ADS)

    Aidun, Daryush K.

    2001-02-01

    The corrosion resistance of a newly developed iron-base, Fe-Mn-Al austenitic, and duplex weld metal has been examined in the NACE solution consisting of 5 wt.% NaCl, 0.5 wt.% acetic acid, and the balance distilled water. The electrochemical techniques such as potentiodynamic polarization, Tafel plots, linear polarization, cyclic polarization, and open-circuit potential versus time were employed. The Fe-Mn-Al weld metals did not passivate and exhibited high corrosion rates. Fe-Cr-Ni (310 and 316) weld and base metals were also examined in the NACE solution at room temperature. The 310 and 316 base metals were more resistant to corrosion than the as-welded 310 and 316 weld metals. Postweld heat treatment (PWHT) improved the corrosion performance of the Fe-Mn-Al weld metals. The corrosion resistance of Fe-Mn-Al weld metals after PWHT was still inferior to that of the 310 and 316 weld and base metals.

  8. Kornerupine in Mg-Al-rich gneisses from Namaqualand, South Africa: mineralogy and evidence for late-metamorphic fluid activity

    NASA Astrophysics Data System (ADS)

    Waters, D. J.; Moore, J. M.

    1985-12-01

    Three kornerupine occurrences are reported in distinctive SiO2-poor, MgO- and Al2O3-rich paragneisses from the Namaqualand Metamorphic Complex in South Africa. Kornerupine coexists stably with phlogopite, cordierite, orthopyroxene, gedrite, sapphirine, sillimanite and plagioclase and, in sapphirine-free rocks, with spinel and corundum. Tourmaline of a texturally older generation than kornerupine is commonly present in the same samples. Ten analysed kornerupines show a variation in total Fe as FeO from 1.8 to 10.9 weight per cent. B2O3 contents are estimated from x-ray data and a few spectrochemical analyses to range from 0.9 to 3.5 weight per cent. There is a strong inverse correlation between B3+ and Al3+. Total iron content has a strong and systematic effect on refractive index, colour and dispersion. Fe and Mg are systematically partitioned with the other minerals, and Mg/(Mg+Fe) ratios increase as follows: spinel Mg-Al-rich, locally boron-bearing, sedimentary precursor.

  9. 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.

  10. 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.

  11. Structural characterization of interfaces in epitaxial Fe/MgO/Fe magnetic tunnel junctions by transmission electron microscopy

    SciTech Connect

    Wang, C.; Chang, L. Y.; Choi, S.-Y.; Kirkland, A. I.; Kohn, A.; Wang, S. G.; Petford-Long, A. K.; Ward, R. C. C.

    2010-07-01

    We present a detailed structural characterization of the interfaces in Fe/MgO/Fe layers grown by molecular-beam epitaxy using aberration-corrected transmission electron microscopy (TEM), scanning TEM, and electron energy-loss spectroscopy. When fabricated into magnetic tunnel junctions, these epitaxial devices exhibit large tunnel magnetoresistance ratios (e.g., 318% at 10 K), though still considerably lower than the values predicted theoretically. The reason for this discrepancy is being debated and has been attributed to the structure of, and defects at the interface, namely, the relative position of the atoms, interface oxidation, strain, and structural asymmetry of the interfaces. In this structural study, we observed that Fe is bound to O at the interfaces. The interfaces are semicoherent and mostly sharp with a minor degree of oxidation. A comparison of the two interfaces shows that the top MgO/Fe interface is rougher.

  12. 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

  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. 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.

  15. Treatment of waste H₂SO₄ with Mg-Al oxide obtained by calcination of NO₃⁻-intercalated Mg-Al layered double hydroxide: Kinetics and equilibrium.

    PubMed

    Kameda, Tomohito; Fubasami, Yuki; Yoshioka, Toshiaki

    2012-01-01

    Mg-Al oxide obtained by calcination of NO(3)(-)-intercalated Mg-Al layered double hydroxide (NO(3)•Mg-Al LDH) was used to treat H(2)SO(4), acting as both a neutralizer of the acid and a fixative for SO(4)(2-). The fraction of SO(4)(2-) removed increased with time and with increasing Mg-Al oxide quantity and temperature. The rate of SO(4)(2-) removal followed first-order kinetics with apparent rate constants of 2.0 × 10(-3), 4.4 × 10(-3), and 5.3 × 10(-2) min(-1) at 10, 30, and 60°C, respectively. The apparent activation energy was 52.1 kJ mol(-1), confirming that the SO(4)(2-) removal by Mg-Al oxide proceeded under chemical reaction control. Furthermore, the adsorption isotherm of SO(4)(2-) by Mg-Al oxide obeyed the Langmuir equation. The maximum adsorption amount was 2.0 mmol g(-1), or 4.0 meq g(-1), indicating that Mg-Al oxide has a large capacity for uptake of SO(4)(2-) from H(2)SO(4). PMID:22416865

  16. Comparison of Fe-AlPILC and Fe-ZSM-5 catalysts used for degradation of methomyl

    NASA Astrophysics Data System (ADS)

    Lázár, Károly; Tomašević, Andjelka; Bošković, Goran; Kiss, Ernő

    2009-07-01

    Catalytic performances of Fe-AlPILC (14 wt.% Fe) and Fe-ZSM-5 (5 wt.% Fe) catalysts are compared in the wet oxidative degradation of methomyl. Fe-ZSM-5 exhibits outstanding whereas Fe-AlPILC shows only mediocre activity. Positions of iron are analysed in the two catalysts by Mössbauer spectroscopy. Iron is in highly dispersed state in Fe-AlPILC whereas in the other case a hematite/ZSM-5 composite is formed. The catalytic activity is attributed to iron located and stabilized in ionic dispersion.

  17. 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.

  18. Equation of State and Spin Transition of (Mg,Fe)O at High Pressures

    NASA Astrophysics Data System (ADS)

    Solomatova, N. V.; Jackson, J. M.; Sturhahn, W.; Zhao, J.; Toellner, T.; Kalkan, B.; Wicks, J. K.; Steinhardt, W.

    2014-12-01

    Earth's lower mantle occupies more than half of Earth's volume, and is composed primarily of bridgmanites and (Mg,Fe)O "ferropericlase." Knowledge of the behavior of lower mantle minerals is essential for interpreting complexity in the deep Earth. Although it is suggested that (Mg,Fe)O represents a major volume fraction of Earth's interior, the iron concentration of (Mg,Fe)O is not very well constrained at all depths of the lower mantle. Near the base of the lower mantle, an enhanced iron content may be found due to melting events in Earth's history and/or reactions with the iron-dominant liquid outer core. Here we examine the high-pressure behavior of polycrystalline (Mg,Fe)O containing 48 mol% FeO ("FP48"), loaded hydrostatically with neon as a pressure medium. Using x-ray diffraction and synchrotron Mössbauer spectroscopy we measure the equation of state of FP48 to about 80 GPa at 300 K and hyperfine parameters to 100 GPa at 300 K, respectively. A gradual volume drop is observed between ˜55 and 75 GPa. To confirm that the observed volume drop is due to a spin crossover, the quadrupole splitting (QS) and isomer shift (IS) of Fe2+ are determined as a function of pressure. At low pressures, our spectra are fitted with two Fe2+-like sites. At pressures between 43 and 81 GPa, an additional Fe2+-like site with a QS of 0 is required, indicative of low-spin iron. Above 93 GPa, two low-spin Fe2+-like sites explain the data well, signifying the completion of the spin crossover. Using a spin crossover equation of state, we have determined the volume drop at the calculated transition pressure and the relevant elastic properties of FP48. Our results are compared to previous measurements of (Mg,Fe)O with varying concentrations of iron at high pressures.

  19. 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.

  20. 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

  1. 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.

  2. Microstructure-property relationships in low-density Al-Li-Mg alloys

    SciTech Connect

    Buchheit, T.E.; Wert, J.A. )

    1993-04-01

    The present article describes an investigation of the microstructure and tensile properties of cast Al-Li-Mg alloys with very low densities, in the range 2.3 to 2.4 Mg/m[sup 3]. Low density is achieved by adding Li and Mg in excess of the solubility limit, which prevents subsequent dissolution of the Al[sub 2]LiMg particles that form during solidification. A simple model developed during the course of this research allows prediction of the volume fraction of Al[sub 2]LiMg and alloy density from alloy composition. The model was used to select two alloy compositions for detailed investigation: Al12Li6Mg and Al16Li8Mg. The microstructures of the cast alloys consist of coarse Al[sub 2]LiMg particles embedded in an Al matrix containing Al[sub 3]Li particles. Both alloys exhibit low tensile elongation in the as-cast condition. Additional processing steps were used to modify the microstructural characteristics thought to be responsible for the low tensile elongation of the as-cast alloys. The Al16Li8Mg alloy, with an Al[sub 2]LiMg volume fraction of 0.25, does not exhibit increased tensile elongation as a result of processing, and the brittle nature of this material is attributed to the high volume fraction of the Al[sub 2]LiMg phase. The Al12Li6Mg alloy, with an Al[sub 2]LiMg volume fraction of 0.13, exhibits a remarkable increase in tensile elongation after extrusion, an effect attributed to fragmentation and dispersal of a three-dimensional (3-D) network of the intermetallic phase in the as-cast alloy.

  3. 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.

  4. Texture evolution of Al-Mg-Li aeronautical alloys in in-situ tension

    NASA Astrophysics Data System (ADS)

    Chen, Zhong-wei; Zhao, Jing; Li, Shi-shun

    2012-12-01

    Texture evolution in extruded and hot-rolled Al-Mg-Li aeronautical alloys during in-situ tension was investigated by using electron backscattered diffraction (EBSD). A field emission scanning electron microscope (FE-SEM) and a MICROTEST-5000 tensile stage were used to carry out in-situ tension tests and observations. The crystallographic texture of the extruded sample changed from weak cube texture {001}<100> to texture {018}<081> during tension fracture. However, strong Brass {110}<112> in the hot-rolled sample was modified into a mixture texture component of Brass {110}<112> and S {123}<634> during tension fracture. Texture evolution in the two samples during tension can be explained by the rotation of grain orientation.

  5. 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)

  6. Electrical spin injection and detection in Fe/MgO/Si: influence of interface states

    NASA Astrophysics Data System (ADS)

    Pu, Yong; Beardsley, Jonas; Swartz, Adrain; Odenthal, Patrick; Berger, Andrew; Ko, Dongkyun; Bhallamudi, Vydia; Hammel, Chris; Kawakami, Roland; Johnston-Halperin, Ezekiel; Pelz, Jon

    2012-02-01

    We report electrical spin injection and detection in Fe/MgO/Si tunnel diodes using a 3-terminal (3T) geometry. Analysis of our Hanle curves yields an effective spin life-time of ˜0.1 ns and a spin-RA product ˜1 Mφ*μm^2, both of which are in rough agreement with previous 3T studies. However, according to our analysis the spin-RA is ˜ 6 orders of magnitude larger than expectations for bulk Si, and the 0.1 ns effective spin life-time is much smaller than reported value in Si by ESR or non-local methods. Here we provide a detailed analysis of electrical injection and detection in the 3T geometry. We present an alternative expression for the 3T spin signal than is usually used, and we propose that spin is accumulating in localized states (LS) at the MgO/Si interface rather than just in bulk Si. Incorporating a theory of spin accumulation in LS developed by M. Tran et al (PRL 102, 036601), we propose an energy distribution for the density of localized states, and introduce a model that agrees well with our anomalously large spin-RA and can explain the strong bias dependence of both spin and charge transport.

  7. 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.

  8. Disproportionation of (Mg,Fe)SiO3 into MgSiO3 perovskite and an Fe-rich hexagonal silicate in the deep lower mantle

    NASA Astrophysics Data System (ADS)

    Zhang, L.; Meng, Y.; Yang, W.; Wang, L.; Mao, W. L.; Zeng, Q. C.; Jeong, J.; Wagner, A. J.; Mkhoyan, K.; Liu, W.; Xu, R.; Mao, H.

    2013-12-01

    Models of the Earth's deep interior have been built upon the basic assumption that the lower mantle down to the top of the D″ layer mainly consists of orthorhombic perovskite (pv) with nominally 10 mol% Fe. Using a laser-heated diamond anvil cell, our experiments at pressures of 95-105 GPa and temperatures of 2200~2400 K show that such perovskite is unstable; it loses its Fe and disproportionates into a nearly Fe-free MgSiO3 pv and an Fe-rich (Mg,Fe)SiO3 phase with a previously unknown hexagonal structure, causing a small volume reduction. Using the newly developed high-pressure multigrain crystallography technique, we have identified 154 individual crystallites belonging to the hexagonal phase in one experiment, each has a unique orientation matrix with as many as 27 diffraction spots that gives identical unit-cell parameters, while 130 individual crystallites of the coexisting pv phase were indexed to the known Pbnm space group. This new mineral physics observation leads to a fresh view on geophysical, geochemical and geodynamic paradigms for the lower mantle below 2000 kilometers depth.

  9. 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

  10. 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. PMID:26684139

  11. 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

  12. 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.

  13. 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. PMID:26223022

  14. 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.

  15. Effect of Fe on the Elastic Constants of Magnesiowustite [(Mg,Fe)O] at Ambient Conditions and High Pressure

    NASA Astrophysics Data System (ADS)

    Sinogeikin, S. V.; Reichmann, H. J.; Bass, J. D.; Mackwell, S. J.; Jacobsen, S. D.

    2001-12-01

    Magnesiowustite is a major mineral in the lower mantle of the Earth. While the effect of temperature and pressure on the elasticity of MgO is well constrained, the effect of Fe on the elastic constants and their pressure derivatives is still uncertain, especially for compositions close to the Mg end-member. Here we present the Brillouin spectroscopy measurements of the single-crystal elastic constants of magnesiowustite at ambient conditions ( ~5.8 mol.% Fe) and to high pressures up to about 10 GPa ( ~1.3 mol.% Fe). The single-crystal samples were prepared by Mg:Fe interdiffusion between periclase single crystals and magnesiowustite powders with carefully controlled oxygen fugacity. The Brillouin scattering measurements were performed in platelet symmetric geometry, which significantly increases the accuracy, and is calibrated with respect to standard periclase sample. High-pressure measurements were performed in a large optical opening Merrill-Basset type diamond anvil cell with Methanol-Ethanol-Water mixture as a pressure-transmitting medium. The new results confirm earlier single-crystal ultrasonic measurements (gigahertz interferometry) which indicated that the behavior of the elastic moduli of magnesiowustite are highly nonlinear in Mg-rich end. A pronounced decrease in acoustic velocities with increasing Fe content is especially obvious in samples with Fe contents of <10 mol. %. The pressure derivatives of the elastic moduli of the sample with XFe = 1.3 mol % are equal to those of periclase within the experimental uncertainties, although the Fe content of the sample may be too small to allow compositional trends to be clearly identified.

  16. Structure of liquid Al and Al67Mg33 alloy: comparison between experiment and simulation

    NASA Astrophysics Data System (ADS)

    Kramer, M. J.; Mendelev, M. I.; Asta, M.

    2014-06-01

    We report data on the structure of liquid Al and an Al67Mg33 alloy obtained from state-of-the-art X-ray diffraction experiments and ab initio molecular dynamics (AIMD) simulations. To facilitate a direct comparison between these data, we develop a method to elongate the AIMD pair correlation function in order to obtain reliable AIMD structure factors. The comparison reveals an appreciable level of discrepancy between experimental and AIMD liquid structures, with the latter being consistently more ordered than the former at the same temperature. The discrepancy noted in this study is estimated to have significant implications for simulation-based calculations of liquid transport properties and solid-liquid interface kinetic properties.

  17. 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.

  18. High-Pressure Brillouin Measurements on Single-Crystal Ferropericlase, (Mg0.94Fe0.06)O: Implications for Earth's Lower Mantle

    NASA Astrophysics Data System (ADS)

    Jackson, J. M.; Bass, J. D.; Sinogeikin, S. V.; Jacobsen, S. D.; Reichmann, H.-; Mackwell, S. J.

    2003-12-01

    The determination of accurate compositional models of Earth's interior from observed seismological data requires knowledge of the elastic properties of candidate phases under conditions approaching those of Earth's interior. Ferropericlase, (Mg,Fe)O, is expected to coexist with silicate perovskite in Earth's lower mantle (660 ­C 2900 km depth), and will therefore have a major influence on all properties in this region of the Earth. However, the effect of iron on the single-crystal elasticity of MgO at high-pressures is still poorly constrained. In this contribution, we present the single-crystal elastic properties of ferropericlase, (Mg0.94Fe0.06)O [hereafter referred to as Fe6], measured by Brillouin scattering on a sample compressed to 13.3(4) GPa with a diamond anvil cell. Within the uncertainties, we find that at room-pressure the bulk modulus of Fe6 is unchanged from MgO, but that the shear modulus of Fe6 is about 7% less than that of MgO. Furthermore, the elastic anisotropy of Fe6 is about 10% greater than that of MgO at room-pressure, in excellent agreement with results obtained using gigahertz ultrasonic interferometry on the same sample [1]. Our measurements also allow us to assess the effect of iron on the pressure derivatives of the sound velocities and elastic moduli of MgO. Results indicate that 6 mol% Fe in MgO does not significantly affect the pressure derivatives of the aggregate elastic properties of ferropericlase compared to MgO. At the highest pressure obtained in this experiment, the elastic anisotropy of Fe6 is close to that of MgO. In light of these new high-pressure measurements on Fe6 and other recent measurements on Al-bearing MgSiO3 perovskite [2], implications for the mineralogy of Earth's lower mantle will be discussed. References: [1] S.D. Jacobsen et al. (2002) J. Geophys. Res., 107, 2001JB000490 [2] J.M. Jackson et al. (2003) Geophys. Res. Abstr., 5, EGS-AGU-EUG Joint Assembly, France, EAE03-A-12122.

  19. 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.

  20. 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

    2016-06-01

    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.

  1. 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.

  2. 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

  3. 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.

  4. Composition and solidification microstructure selection in the interdendritic matrix between primary Al{sub 3}Fe dendrites in hypereutectic Al-Fe alloys

    SciTech Connect

    Liang, D.; Korgul, P.; Jones, H.

    1996-07-01

    The composition and constitution of matrix microstructure between plate-like Al{sub 3}Fe dendrites in Bridgman-grown hypereutectic Al-Fe alloys has been determined as a function of alloy concentration C{sub 0} and growth velocity V in the ranges 2.5 < C{sub 0} < 28.1 wt%Fe and 0.01 < V < 5.0 mm/s. The transition at V = 0.1 mm/s from a fully eutectic matrix at C{sub 0} = 3.5 wt%Fe to one containing {alpha}Al dendrites at C{sub 0} {ge} 4.7 wt%Fe is attributed to growth temperatures of {alpha}Al dendrites that are higher than those of eutectic in a matrix of lower iron-content, which results from these conditions. The matrix eutectic changes from irregular {alpha}-Al-Al{sub 3}Fe to regular {alpha}Al-Al{sub x}Fe with increasing V, the transition velocity increasing from 0.1 to 0.2 mm/s for C{sub 0} values of 9.5 and 14 wt%Fe up to 0.35--1.0 mm/s for C{sub 0} values of 18.7--28.1 wt%Fe. This increased transition velocity, compared with that for {alpha}-Al-Al{sub 3}Fe to {alpha}Al-Al{sub 6}Fe at lower concentration, is indicative of a lower formation temperature for the {alpha}Al-Al{sub x}Fe than the {alpha}Al-Al{sub 6}Fe eutectic.

  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. Low cycle fatigue of FeAl(42 at. % Al) at room temperature

    SciTech Connect

    Hanes, D.B.; Gibala, R.

    1997-12-31

    The monotonic mechanical behavior in tension and compression of FeAl has been well documented. However, very little work has been done on the cyclic deformation behavior of this material. In this work, the behavior of FeAl (42 at. % Al) under low cycle fatigue was studied, including the effects of test environments and surface coatings. It was found that the fatigue life of this alloy is limited by environmental embrittlement. This embrittlement process can be equally well prevented by deformation in an oxygen environment or by coating the alloy with a protective film. The type of film applied appears to have little effect. Similar results were seen in monotonic testing.

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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.

  12. Influence of homogenization and artificial aging heat treatments on corrosion behavior of Mg-Al alloys

    SciTech Connect

    Beldjoudi, T.; Fiaud, C.; Robbiola, L. . Lab. d'Etudes de la Corrosion)

    1993-09-01

    The influence of heat treatment on corrosion behavior of magnesium-aluminum (Mg-9Al) alloys was investigated by studying the electrochemical properties of Mg-9Al in the solution-treated (T4) and artificially aged (T6) conditions. The alloys' properties were compared to those of pure Mg, the intermetallic Mg[sub 17]Al[sub 12] phase, and different Mg-Al-based alloys (Mg-3Al, AZ91). The Mg-9Al alloy exhibited better corrosion resistance in the T6 condition than in the T4 condition because of the intermetallic Mg[sub 17]Al[sub 12] precipitates present n the T6 alloy. The mechanism responsible for this behavior was attributed to a more protective porous film on the T6 matrix alloy than on the T4 alloy. Addition of zinc did not modify these results. Localized corrosion testing showed the Mg-Al alloys were attacked preferentially in relation to magnesium silicide (Mg[sub 2]Si) precipitates which were characterized clearly using metallurgical examinations.

  13. Tunneling Anisotropic Magnetoresistance in Fe Nanoparticles Embedded in MgO Matrix

    NASA Astrophysics Data System (ADS)

    Pham, T. V.; Miwa, S.; Suzuki, Y.

    2016-05-01

    The tunnel magnetoresistance (TMR) effect is related to the relative orientation of the magnetizations of the two ferromagnetic electrodes in magnetic tunnel junctions (MTJs). The tunnel anisotropic magnetoresistance (TAMR) effect is related to the orientation of the magnetization with respect to the current direction or the crystallographic axes. Beyond the TMR, the TAMR is not only present in MTJs in which both electrodes are ferromagnetic but may also appear in tunnel structures with a single magnetic electrode. We investigated the magnetotransport properties in an Au/MgO/Fe nanoparticles/MgO/Cu tunnel junction. We found that both the TMR and TAMR can appear in tunnel junctions with Fe nanoparticles embedded in an MgO matrix. The TMR is attributed to spin-dependent tunneling between Fe nanoparticles, so the device resistance depends on the magnetization directions of adjacent Fe nanoparticles. The TAMR is attributed to the interfacial spin-orbit interaction, so the device resistance depends on each magnetization direction of an Fe nanoparticle. This is the first observation of the TAMR in Fe nanoparticles embedded in an MgO matrix.

  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. Evidence for an equilibrium epitaxial complexion at the Au-MgAl2O4 interface

    NASA Astrophysics Data System (ADS)

    Majdi, Tahereh; Zhu, Guo-zhen; Carvalho, Jessica; Jarvis, Victoria; Meinander, Kristoffer; Britten, James F.; Botton, Gianluigi; Preston, John S.

    2015-12-01

    Evidence for the existence of an equilibrium epitaxial complexion at the Au-MgAl2O4 interface has been observed. The growth of crystalline MgAl2O4 nanostructures, from a previously stable substrate in the presence of an Au overlayer and heat, is associated with this complexion. Prior to the nanostructures' self-assembly, Au nanoparticles crystalize, then reorient to align with the MgAl2O4 substrate. The presented results contradict earlier conclusions based solely on SEM studies of the final assembled nanostructures. Those results suggested that the MgAl2O4 grown pedestal and associated Au nanoparticle atop were both gold.

  16. High noise suppression using magnetically isotropic (CoFe-AlN)/(AlN) multilayer films

    NASA Astrophysics Data System (ADS)

    Kijima, Hanae; Ohnuma, Shigehiro; Masumoto, Hiroshi; Shimada, Yutaka; Endo, Yasushi; Yamaguchi, Masahiro

    2015-05-01

    Magnetically isotropic (CoFe-AlN)n/(AlN)n+1 multilayer films, in which the number of CoFe-AlN magnetic layers n ranged from 1 to 27, were prepared by radio frequency sputtering to achieve noise suppression at gigahertz frequencies. The soft CoFe-AlN magnetic layers consisted of nanometer-sized CoFe ferromagnetic grains embedded in an insulating AlN amorphous matrix, while the insulating AlN layers comprised AlN columnar crystals. All films showed a similar frequency dependence of permeability and ferromagnetic resonance of 1.7 GHz. Noise suppression was evaluated using a microstrip line as a noise source by determining the in-line conductive loss and the near-field intensity picked up by magnetic field detective probes. High noise suppression effects were observed in every direction in the film plane. Maximum noise suppression values amounted to 60% for the in-line conductive loss and -20 dB for the magnetic near-field intensity at around 1.7 GHz in the 27-layer film. These high-frequency noise suppression levels may be attributed to eddy current losses and ferromagnetic resonance.

  17. Corrosion performance of Fe-Cr-Al and Fe aluminide alloys in complex gas environments

    SciTech Connect

    Natesan, K.; Johnson, R.N.

    1995-05-01

    Alumina-forming structural alloys can offer superior resistance to corrosion in the presence of sulfur-containing environments, which are prevalent in coal-fired fossil energy systems. Further, Fe aluminides are being developed for use as structural materials and/or cladding alloys in these systems. Extensive development has been in progress on Fe{sub 3}Al-based alloys to improve their engineering ductility. In addition, surface coatings of Fe aluminide are being developed to impart corrosion resistance to structural alloys. This paper describes results from an ongoing program that is evaluating the corrosion performance of alumina-forming structural alloys, Fe-Al and Fe aluminide bulk alloys, and Fe aluminide coatings in environments typical of coal-gasification and combustion atmospheres. Experiments were conducted at 650-1000{degrees}C in simulated oxygen/sulfur gas mixtures. Other aspects of the program are corrosion evaluation of the aluminides in the presence of HCl-containing gases. Results are used to establish threshold Al levels in the alloys for development of protective alumina scales and to determine the modes of corrosion degradation that occur in the materials when they are exposed to S/Cl-containing gaseous environments.

  18. Study of CoFeB thickness and composition dependence in a modified CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction

    NASA Astrophysics Data System (ADS)

    Zhu, M.; Chong, H.; Vu, Q. B.; Brooks, R.; Stamper, H.; Bennett, S.

    2016-02-01

    We studied the CoFeB thickness and composition dependence of tunneling magnetoresistance (TMR) and resistance-area product (RA) in a modified CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction (MTJ), in which the bottom CoFeB is coupled to an in-plane exchange biased magnetic layer. This stack structure allows us to measure TMR and RA of the MTJs in sheet film format without patterning them, using current-in-plane-tunneling (CIPT) technique. The thickness ranges for both top and bottom CoFeB to exhibit perpendicular magnetic anisotropy are similar to what are seen in each single magnetic film stack. However, CIPT measurement revealed that there exists an optimal thickness for both top and bottom CoFeB to achieve the highest TMR value. Magnetic hysteresis loops also suggest the thickness-dependent coupling between the top and bottom CoFeB layers. We studied MTJs with two CoFeB compositions (Co40Fe40B20 and Co20Fe60B20) and found that Co20Fe60B20 MTJs give higher TMR and also wider perpendicular thickness range when used at the top layer.

  19. Effect of annealing and applied bias on barrier shape in CoFe/MgO/CoFe tunnel junctions.

    SciTech Connect

    Liu, Y.; Chiaramonti, A. N.; Schreiber, D. K.; Yang, H.; Parkin, S. S. P.; Heinonen, O. G.; Petford-Long, A. K.

    2011-04-12

    Energy-filtered transmission electron microscopy and electron holography were used to study changes in the MgO tunnel barrier of CoFe/MgO/CoFe magnetic tunnel junctions (MTJs) as a function of annealing and in situ applied electrical bias. Annealing was found to increase the homogeneity and crystallinity of the MgO tunnel barrier. Cobalt, oxygen, and trace amounts of iron diffused into the MgO upon annealing. Annealing also resulted in a reduction of the tunneling barrier height, and decreased the resistance of the annealed MTJ relative to that of the as-grown sample. In situ off-axis electron holography was employed to image the barrier potential profile of a MTJ directly, with the specimen under electrical bias. Varying the bias voltage from -1.5 to +1.5 V was found to change the asymmetry of the barrier potential and decrease the effective barrier width as a result of charge accumulation at the MgO-CoFe interface.

  20. 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.

  1. 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

  2. In situ high pressure infrared study of the carbon environment in (Mg,Fe)CO3 carbonate

    NASA Astrophysics Data System (ADS)

    Boulard, E.; Pan, D.; Galli, G.; Mao, W. L.

    2013-12-01

    Carbonates are likely to be the main carbon-bearing phase in the Earth's mantle, and therefore knowledge of their mineral physics down to core mantle boundary conditions is critical for understanding the deep carbon cycle. (Mg,Fe)CO3 has been the focus of many recent high pressure studies which indicate several crystallographic changes. An electronic spin transition in the iron end-member has been reported at approximately 45 GPa. As a result, a change in the volume and the equation of state, and moreover a change in the rate of C-O bond distortion were described by X-ray diffraction (XRD) studies (B. Lavina et al., 2009; 2010). At higher pressures, above 80 GPa, we have observed the transformation of (Mg,Fe)CO3 carbonate into a new high-pressure high-temperature phase by in situ XRD (Boulard et al., 2011). Investigation of the carbon environment had previously been limited to ex situ studies at ambient conditions after releasing the pressure on the sample. Spectroscopy on the carbon C-k edge indicated a potential change in the carbon environment, and a transformation of the carbonate trigonal CO3 groups into CO4 tetrahedra had been proposed (Boulard et al., 2011). However this interpretation is still under debate. To follow the evolution of C-O bonds and clarify the existence of CO4 tetrahedra in high-pressure carbonate phases, we combined in-situ infrared spectroscopy with theoretical calculations. Mid-infrared spectroscopy, performed at high pressure before and after laser heating at U2A, NSLS, BNL show several changes in the (Mg,Fe)CO3 spectrum after laser heating at 103 GPa. We will discuss the interpretation of these new spectroscopic signatures and the possibility of a dramatic change in the carbon environment. References: Boulard, E. et al., (2011). New host for carbon in the deep Earth. PNAS, 108(13), 5184-5187. Lavina, B. et al., (2009). Siderite at lower mantle conditions and the effects of the pressure-induced spin-pairing transition. Geophysical

  3. 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.

  4. Screened moments and absence of ferromagnetism in FeAl

    NASA Astrophysics Data System (ADS)

    Galler, A.; Taranto, C.; Wallerberger, M.; Kaltak, M.; Kresse, G.; Sangiovanni, G.; Toschi, A.; Held, K.

    2015-11-01

    While the stoichiometric intermetallic compound FeAl is found to be paramagnetic in experiment, standard band-theory approaches predict the material to be ferromagnetic. We show that this discrepancy can be overcome by a better treatment of electronic correlations with density-functional plus dynamical mean-field theory. Our results show no ferromagnetism down to 100 K and since the susceptibility is decreasing at the lowest temperatures studied we also do not expect ferromagnetism at even lower temperatures. This behavior is found to originate from temporal quantum fluctuations that screen short-lived local magnetic moments of 1.6 μB on Fe.

  5. Effect of Al2O3 on the Viscosity and Structure of CaO-SiO2-MgO-Al2O3-FetO Slags

    NASA Astrophysics Data System (ADS)

    Wang, Zhanjun; Sun, Yongqi; Sridhar, Seetharaman; Zhang, Mei; Guo, Min; Zhang, Zuotai

    2015-04-01

    The present paper provided a fundamental investigation on the effect of Al2O3 on the viscosity and structure of CaO-SiO2-MgO-Al2O3-FetO slags for the purpose of efficiently recycling the valuable elements from the steelmaking slags. The results show that the viscosity of CaO-SiO2-Al2O3-MgO-FetO slags slightly increases with increasing Al2O3 content. The degree of the polymerization (DOP) of quenched slags, determined from Raman spectra and magic angle spinning-nuclear magnetic resonance, is also found to increase with increasing Al2O3 content. It can be deduced that the increasing DOP can promote the formation of gehlenite phase (Ca2Al2SiO7), thus facilitating the formation of higher phosphorous (or vanadium) contained solid solution ( n'Ca2SiO4·Ca3((P or V)O4)2). As Al2O3 content increases up to a specific value, the charge compensating ions which present near [AlO4]-tetrahedra and [FeO4]-tetrahedra are not fully supplied due to the scarcity of Ca2+. In this case, the existing Fe3+ in the melt cannot completely form [FeO4]-tetrahedra and part of Fe3+ would form [FeO6]-octahedra to substitute Ca2+ to modify the slags.

  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. 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

  8. 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.

  9. Stable cation inversion at the MgAl2O4(100) surface.

    PubMed

    Rasmussen, Morten K; Foster, Adam S; Hinnemann, Berit; Canova, Filippo F; Helveg, Stig; Meinander, Kristoffer; Martin, Natalia M; Knudsen, Jan; Vlad, Alina; Lundgren, Edvin; Stierle, Andreas; Besenbacher, Flemming; Lauritsen, Jeppe V

    2011-07-15

    From an interplay of atom-resolved noncontact atomic force microscopy, surface x-ray diffraction experiments, and density functional theory calculations, we reveal the detailed atomic-scale structure of the (100) surface of an insulating ternary metal oxide, MgAl2O4 (spinel). We surprisingly find that the MgAl2O4(100) surface is terminated by an Al and O-rich structure with a thermodynamically favored amount of Al atoms interchanged with Mg. This finding implies that so-called Mg-Al antisites, which are defects in the bulk of MgAl2O4, become a thermodynamically stable and integral part of the surface. PMID:21838378

  10. Structure and lattice vibrations of Mg-Al spinel solid solution

    NASA Astrophysics Data System (ADS)

    Ishii, M.; Hiraishi, J.; Yamanaka, T.

    1982-05-01

    X-ray structure refinements have been made for nonstoichiometric (MgO · 3Al2O3) and stoichiometric Mg-Al spinels. Several structure variations with chemical composition have been observed and are discussed in relation to Al substitution in tetrahedral sites. Infrared reflection and Raman spectra of the single crystal of the nonstoichiometric spinel (MgO · 3Al2O3) have been measured and analyzed. The results obtained are compared with those reported for the stoichiometric sample. From the infrared and Raman frequencies reported for the stoichiometric Mg-Al spinel, which are partly complemented with our results, the effective ionic charges of the ions in MgAl2O4 have been estimated on the basis of the rigid ion model.

  11. 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.

  12. Determination of the percolation threshold in Fe/MgO magnetic granular multilayers.

    PubMed

    García-García, A; Vovk, A; Strichovanec, P; Pardo, J A; Magén, C; Algarabel, P A; De Teresa, J M; Morellón, L; Ibarra, M R

    2010-02-10

    The evolution of the morphology, magnetic and transport properties of Fe(t nm)/MgO(3.0 nm) multilayers with respect to the nominal metallic layer thickness was investigated. A comparison with existing experimental data on discontinuous metal-insulator multilayers, ultrathin epitaxial Fe films on MgO substrates and granular cermet films is made. It is confirmed that the deposition conditions and the material composition play a crucial role in the percolation process. Nominal thicknesses of Fe layers at which an infinite metallic cluster is formed and the conditions for continuous Fe coverage were determined. Different methods of percolation threshold detection were analysed. We show that investigation of the temperature dependence of resistance in nanostructures could lead to an overestimation of the percolation threshold value, while magnetic measurements alone could lead to its underestimation. PMID:21386355

  13. Microstructure-property relationships in low-density Al-Li-Mg alloys

    NASA Astrophysics Data System (ADS)

    Buchheit, T. E.; Wert, J. A.

    1993-04-01

    The present article describes an investigation of the microstructure and tensile properties of cast Al-Li-Mg alloys with very low densities, in the range 2.3 to 2.4 Mg/m3. Low density is achieved by adding Li and Mg in excess of the solubility limit, which prevents subsequent dissolution of the Al2LiMg particles that form during solidification. A simple model developed during the course of this research allows prediction of the volume fraction of Al2LiMg and alloy density from alloy composition. The model was used to select two alloy compositions for detailed investigation: A112Li6Mg and A116Li8Mg. The microstructures of the cast alloys consist of coarse Al2LiMg particles embedded in an Al matrix containing Al3Li particles. Both alloys exhibit low tensile elongation in the as-cast condition. Additional processing steps were used to modify the microstructural characteristics thought to be responsible for the low tensile elongation of the ascast alloys. The A116Li8Mg alloy, with an Al2LiMg volume fraction of 0.25, does not exhibit increased tensile elongation as a result of processing, and the brittle nature of this material is attributed to the high volume fraction of the Al2LiMg phase. The A112Li6Mg alloy, with an Al2LiMg volume fraction of 0.13, exhibits a remarkable increase in tensile elongation after extrusion, an effect attributed to fragmentation and dispersal of a three-dimensional (3-D) network of the intermetallic phase in the as-cast alloy.

  14. 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.

  15. 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.

  16. 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.

  17. Protein interactions with corroding metal surfaces: comparison of Mg and Fe.

    PubMed

    Wagener, Victoria; Faltz, Anne-Sophie; Killian, Manuela S; Schmuki, Patrik; Virtanen, Sannakaisa

    2015-01-01

    The influence of bovine serum albumin (BSA) on the electrochemical behaviour of pure Mg and Fe was studied in simulated body fluid (SBF), in view of the possible application of these materials as biodegradable metals. Results indicate a different trend for the BSA-effect on corrosion for the two metals: for Mg, a strong corrosion-inhibiting effect is observed in the presence of BSA in solution, especially for short-term exposure, whereas for Fe only a slight acceleration of corrosion is caused by the addition of BSA to the solution. For both metals, the protein-effect on the electrochemical behaviour shows a complex time-dependence. Surface analysis indicates that stronger BSA adsorption takes place on Mg than on Fe. Moreover, adsorption experiments with BSA and a second protein (lysozyme) were conducted. The results are discussed in view of electrostatic interactions between differently charged metal oxide/hydroxide surfaces and proteins. PMID:25905976

  18. ALS-like skin changes in mice on a chronic low-Ca/Mg high-Al diet.

    PubMed

    Kihira, Tameko; Yoshida, Sohei; Kondo, Tomoyoshi; Yase, Yoshiro; Ono, Seiitsu

    2004-04-15

    Epidemiologic studies of endemic foci of amyotrophic lateral sclerosis (ALS) have shown low concentrations of Ca/Mg and high concentrations of Al/Mn in the drinking water and garden soil, which may play a causative role in the pathogenesis of endemic ALS. We studied the effects of chronic exposure to a low-Ca/Mg high-Al maltol diet on the skin of experimental animals. In ALS patients, atrophy of the epidermis, edematous changes with separated collagen fibrils and an accumulation of amorphous materials between collagen bundles were regarded as pathognomonic skin changes of ALS. Mice chronically fed a low-Ca/Mg high-Al maltol diet showed neuronal degeneration and loss in the spinal cords and cerebral cortices, as well as skin changes including atrophy, separation of collagen fibrils and accumulation of amorphous materials, similar to the skin changes characteristic of ALS. This is the first report of skin changes in animal models similar to those of ALS. We speculate that environmental factors such as chronic low-Ca/Mg high-Al condition play some causative role in the pathogenesis of Kii-ALS. PMID:15050431

  19. 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.

  20. 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

  1. Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures.

    PubMed

    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

  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. In situ XPS investigation of Pt(Sn)/Mg(Al)O catalysts during ethane dehydrogenation experiments

    NASA Astrophysics Data System (ADS)

    Virnovskaia, Anastasia; Jørgensen, Sissel; Hafizovic, Jasmina; Prytz, Øystein; Kleimenov, Evgueni; Hävecker, Michael; Bluhm, Hendrik; Knop-Gericke, Axel; Schlögl, Robert; Olsbye, Unni

    2007-01-01

    Calcined hydrotalcite with or without added metal (Mg(Al)O, Pt/Mg(Al)O and Pt,Sn/Mg(Al)O) have been investigated with in situ X-ray photoelectron spectroscopy (XPS) during ethane dehydrogenation experiments. The temperature in the analysis chamber was 450 °C and the gas pressure was in the range 0.3-1 mbar. Depth profiling of calcined hydrotalcite and platinum catalysts under reaction, oxidation and in hydrogen-water mixture was performed by varying the photon energy, covering an analysis depth of 10-21 Å. It was observed that the Mg/Al ratio in the Mg(Al)O crystallites does not vary significantly in the analysis depth range studied. This result indicates that Mg and Al are homogeneously distributed in the Mg(Al)O crystallites. Catalytic tests have shown that the initial activity of a Pt,Sn/Mg(Al)O catalyst increases during an activation period consisting of several cycles of reduction-dehydrogenation-oxidation. The Sn/Mg ratio in a Pt,Sn/Mg(Al)O catalyst was followed during several such cycles, and was found to increase during the activation period, probably due to a process where tin spreads over the carrier material and covers an increasing fraction of the Mg(Al)O surface. The results further indicate that spreading of tin occurs under reduction conditions. A PtSn 2 alloy was studied separately. The surface of the alloy was enriched in Sn during reduction and reaction conditions at 450 °C. Binding energies were determined and indicated that Sn on the particle surface is predominantly in an oxidised state under reaction conditions, while Pt and a fraction of Sn is present as a reduced Pt-Sn alloy.

  5. 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.

  6. 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.

  7. 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}.

  8. 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.

  9. 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

  10. 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

  11. Microstructure selection maps for Al-Fe alloys

    SciTech Connect

    Gilgien, P.; Zryd, A.; Kurz, W.

    1995-09-01

    The solidification microstructures for Al-0.5-4 at.% Fe alloys under constrained growth conditions have been calculated using analytical models of the growth kinetics of dendritic, eutectic and plane front interface morphologies of stable and metastable phases. Laser remelting experiments are carried out on an Al-4 at.% Fe alloy with low beam velocity (10 mm/s) in order to complete previous experimental results on the solidification microstructures obtained at intermediate growth rates by Bridgman experiments and at a high growth rates by rapid laser resolidification. Comparison of predicted with experimentally determined solidification microstructure maps shows satisfactory agreement in view of the limited knowledge of the thermophysical properties of this system. These maps are useful for the interpretation of microstructures and phases forming under medium to high solidification rates and for the understanding and development of rapid solidification processing. Further the modeling is useful for improving available phase diagram information.

  12. Enhanced Tunneling Magnetoresistance in Voltage-controlled CoFeB/MgO Junctions

    NASA Astrophysics Data System (ADS)

    Almasi, Hamid; Xu, Meng; Gentry, Christian; Yu, Di; Newhouse-Illige, Ty; Liu, Y. H.; Freeland, J. W.; Velthuis, S. G. E. Te; Wang, Weigang

    2015-03-01

    Perpendicular magnetic anisotropy (PMA) at the CoFeB/MgO interface originates from the hybridization of d orbitals of Fe and Co and the Pz orbital of Oxygen. Due to different electronic band structures, the hybridization of the d orbitals of Fe and Co is likely different, therefore contributing unequally to the total PMA. This difference has been probed by an X-ray magnetic circular dichroism (XMCD). The orbital moment of Fe was found to be much larger than that of Co by XMCD.These results demonstrated that Fe contributes most to the PMA at the interface. MTJs with Fe-rich electrodes were fabricated and a substantially larger PMA was achieved. With further optimization in post-growth thermal annealing, we have achieved over 150% TMR in these voltage-controllable CoFeB/MgO MTJs. This work was supported in part by NSF (ECCS-1310338) and by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA. Work at ANL was supported by the DOE-BES, MSE and SUF.

  13. 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.

  14. Thermodynamically destabilized hydride formation in "bulk" Mg-AlTi multilayers for hydrogen storage.

    PubMed

    Kalisvaart, Peter; Shalchi-Amirkhiz, Babak; Zahiri, Ramin; Zahiri, Beniamin; Tan, XueHai; Danaie, Mohsen; Botton, Gianluigi; Mitlin, David

    2013-10-21

    Thermodynamic destabilization of MgH2 formation through interfacial interactions in free-standing Mg-AlTi multilayers of overall "bulk" (0.5 μm) dimensions with a hydrogen capacity of up to 5.5 wt% is demonstrated. The interfacial energies of Mg-AlTi and Mg-Ti (examined as a baseline) are calculated to be 0.81 and 0.44 J m(-2). The enhanced interfacial energy of AlTi opens the possibility of creating ultrathin alloy interlayers that provide further thermodynamic improvements in metal hydrides. PMID:23955681

  15. 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.

  16. First-principle Simulation of Magnesium-aluminum Spinel (MgAl2O4)

    NASA Astrophysics Data System (ADS)

    Zhang, W.; Seagle, C. T.; Zhou, H.; Heinz, D. L.

    2008-12-01

    11033768 First-principle Simulation of Magnesium-aluminum Spinel (MgAl2O4) Materials with the spinel crystal structure, AB2O4 are believed to be an important component of Earth's mantle and may be related to density and seismic wave velocity discontinuities at the transition zone from 400km to 660km depth. Using Ab-initio calculations, five phases are predicted to have a stability range at zero temperature: magnesium-aluminum spinel (MgAl2O4), two of its polymorphs, which are of Pbnm and Cmcm space groups, periclase (MgO) and corundum (Al2O3). Pbnm-MgAl2O4 has the calcium-ferrite structure and Cmcm-MgAl2O4 takes the calcium-titanate structure. Calculations are preformed using the PWSCF (Plane-Wave Self-Consistent Field) codes. The free energy of the compressed volume was calculated directly for each of the phases above. Based on the energy-volume results from the calculations, dissolution of MgAl2O4 into MgO + Al2O3 occurs at 12GPa and the mixture (MgO + Al2O3) is expected to recombine to form the calcium-ferrite type phase at about 27GPa. The two phase transition pressures are consistent with experimental results. Cell parameters of the five phases simulated and their bulk modulus derived from the energy-volume curve are also in good agreement with experimental work. But unlike the conclusions drawn from some previous experimental work, the calcium-ferrite type structure (Pbnm-MgAl2O4) did not transform to the calcium-titanate type structure (Cmcm-MgAl2O4) at around 40GPa, which provides the possibility that calcium-ferrite type phase may be stable to even higher pressures (up to100GPa). Derived parameters, bulk modulus and density of each phase are in good agreement with experimental results. The differences are within 4%. Compared to seismic velocity profiles of the earth, these phase transitions pressures match the discontinuity pressures at transition zone 400km (Fd3m- MgAl2O4 -> MgO + Al2O3) and 660km (MgO + Al2O3 -> Pbnm-MgAl2O4) respectively, suggesting

  17. Tensile properties of Fe-16 at. % Al alloys

    SciTech Connect

    Sikka, V.K.

    1995-02-01

    A newly developed melting method for Fe-16 at. % Al alloy (FAPY) is described. Tensile data on the air-induction-melted (AIM) and vacuum-induction-melted (VIM) heats of FAPY after identical processing are presented. Optical, scanning electron micrographs (SEM), and microprobe analysis were carried out to explain the lower room-temperature ductility and more scatter in the data for the AIM material as opposed to the VIM material.

  18. 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.

  19. Sound Velocities at the Spin Crossover in (Mg0.75Fe0.25)O Ferropericlase

    NASA Astrophysics Data System (ADS)

    Sturhahn, W.; Lin, J.; Jackson, J. M.; Zhao, J.

    2006-12-01

    Iron-bearing minerals of the lower mantle like ferropericlase and silicate perovskite have recently been studied to evaluate the presence of pressure-dependent crossovers between the high-spin and the low-spin state of iron. Such a crossover was clearly observed in ferropericlase using x-ray emission spectroscopy [1,2], conventional Mössbauer spectroscopy [3], and synchrotron Mössbauer spectroscopy [4]. In the case of silicate perovskite, the electronic state of the iron has been studied with x-ray emission spectroscopy [5,6] and synchrotron Mössbauer spectroscopy [7] but the situation remains unclear. Also the influence of the spin crossover on sound velocities of the iron-bearing minerals of the lower mantle has not been studied experimentally. We applied nuclear resonant inelastic x-ray scattering to determine the vibrational density of states of Fe in (Mg0.75Fe0.25)O ferropericlase up to 110 GPa and ambient temperature. We observed a significant effect of the spin crossover in ferropericlase on its elasticity and sound velocities that can derived from the vibrational density of states. We will also briefly address the potential effects of high temperatures on the spin crossover in the framework of a recently suggested thermal population model [8]. This work is supported by the U.S. DOE-BES, Office of Science, under Contract No. W-31-109-Eng-38 and by NSF through COMPRESS. [1] Badro J. et al. (2003) Science 300, 789 [2] Lin J.-F. et al. (2005) Nature 436, 377 [3] Speziale S. et al. (2005) PNAS 102, 17918 [4] Lin J.-F. et al. (2006) Phys.Rev. B 73, 113107 [5] Li J. et al. (2004) PNAS 101, 14027 [6] Badro J. et al. (2004) Science 305, 383 [7] Jackson J.M. et al. (2005) American Mineral. 90, 199 [8] Sturhahn W. et al. (2005) Geophys.Res.Lett. 31, L12307

  20. 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.

  1. 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.

  2. 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

  3. 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

  4. 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.

  5. 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.

  6. Yield stress anomaly in B2 FeAl

    SciTech Connect

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

    1996-12-31

    The studies on yield stress anomaly of B2 FeAl single crystals are reviewed in this paper. A positive temperature dependence of yield stress, so-called yield stress anomaly, is observed in B2 FeAl in which excess vacancies are fully annealed out. Associated with the anomaly, characteristic asymmetry is found between tension and compression. While the strain-rate sensitivity is almost zero in the temperature range of the yield stress anomaly, the stress relaxation becomes significant with increasing temperature, indicating that a recovery process is thermally activated. It is ascertained by the two-surface trace analysis that slip transition from <111> direction at intermediate temperature to <100> at high temperature occurs around the peak temperature. Even at the peak temperature, in addition, operative slip vector for yielding is confirmed to be predominantly <111> by TEM. Also, it is observed that <111>-type superdislocations are frequently climb-dissociated in the temperature range of the anomaly. APB formation on {l_brace}111{r_brace} plane is energetically favorable, which is in agreement with the Flinn`s calculation for the B2 superlattice that APB energy on {l_brace}111{r_brace} plane is lower than that on {l_brace}110{r_brace} plane. Such an anisotropy of APB energy would offer specific driving force for the climb dissociation on <111> superdislocations. On the basis of the observed results, the anomalous strengthening behavior of B2 FeAl single crystals is discussed.

  7. Removal of borate by coprecipitation with Mg/Al layered double hydroxide

    NASA Astrophysics Data System (ADS)

    Kurashina, Masashi; Inoue, Tatsuki; Tajima, Chihiro; Kanezaki, Eiji

    2015-03-01

    Borate has been used for various industrial products and excessive dose of boron is harmful to humans. We investigated the removal of borate by direct coprecipitation with Mg/Al layered double hydroxide. In this study, the maximum removal of boron was 90% when Mg 30 mmol and Al 15 mmol at pH = 10 were used for 498 mg/l as B. The boron adsorption isotherms could be fitted to Langmuir model. The calculated constant Ws, saturation limit of boron adsorption, is 25 ± 2 mg/g and it is larger than that of ion exchange reaction (Ws = 15±1 mg/g).

  8. 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

  9. Spectroscopic characterisation of the LDH mineral quintinite Mg4Al2(OH)12CO3·3H2O.

    PubMed

    Theiss, Frederick; López, Andrés; Frost, Ray L; Scholz, Ricardo

    2015-11-01

    Raman and infrared spectroscopy coupled with scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) have been applied to study the natural hydrotalcite quintinite Mg4Al2(OH)12[CO3]·3H2O. SEM shows the mineral to be a homogenous phase. Quintinite is composed of Mg and Al as the major elements with minor amounts of Fe. Two Raman bands at 1046 and 1062 cm are assigned to the ν1 symmetric stretching modes of the carbonate anion. Thermal treatment shifts these bands to higher wavenumbers indicating a change in the carbonate bonding. Hydrogen bond distances are calculated using a Libowitzky-type empirical function and varied between 2.61 and 3.00 Å. Stronger hydrogen bonds were formed by water units as compared to the hydroxyl units. PMID:26099827

  10. EELS of colloids in Mg{sup +} implanted MgAl{sub 2}O{sub 4} spinel

    SciTech Connect

    Evans, N.D.; Zinkle, S.J.

    1994-06-01

    During 2-MeV Mg{sup +} implantation at 25 C to 2.8{times}10{sup 21}/m{sup 2}, dislocation loops are formed at midrange depths (0.5-1.0{mu}m) on {l_brace}110{r_brace} and {l_brace}111{r_brace}. No evidence was found for the dark field images to be hexagonal metallic Mg; the colloids are suggested to be either metallic Al or another phase coherent with surrounding spinel. Regression analysis of low-loss spectra and diffraction data are consistent with the colloids in the implanted ion region being metallic Al, although the colloids could be metallic Mg in a metastable cubic structure.

  11. Chemical stability and Ce doping of LiMgAlF6 neutron scintillator

    DOE PAGESBeta

    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.

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. Self-assembled growth and magnetic properties of a BiFeO3-MgFe2O4 nanocomposite prepared by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Kim, Dong Hun; Aimon, Nicolas M.; Ross, Caroline A.

    2013-05-01

    The fabrication and magnetic properties are described for a nano-composite epitaxial thin film system consisting of perovskite phase BiFeO3 and spinel phase MgFe2O4 grown on a (001) SrTiO3 substrate by combinatorial pulsed laser deposition. The MgFe2O4 phase formed well-defined vertical pillars in a BiFeO3 matrix, and both phases were epitaxial with the substrate. The BiFeO3-MgFe2O4 composite films showed soft magnetic behavior and magnetically isotropic properties which is explained by the weak magnetoelastic effects in MgFe2O4.

  17. Electrochemical Codeposition of Al-Li-Mg Alloys at Solid Aluminum Electrode from LiCl-KCl-MgCl2 Molten Salt System

    NASA Astrophysics Data System (ADS)

    Ye, Ke; Zhang, Mi Lin; Chen, Ye; Han, Wei; de Yan, Yong; Cao, Peng

    2010-06-01

    The electrochemical codeposition of Mg and Li at an aluminium electrode in LiCl-KCl (50:50 wt pct) melts containing different concentrations of MgCl2 at 893 K (620 °C) to form Al-Li-Mg alloys was investigated. Cyclic voltammograms showed that the potential of Li metal deposition at an Al electrode, before the addition of MgCl2, is more positive than that of Li metal deposition at an Mo electrode, which indicated the formation of an Al-Li alloy. The underpotential deposition of magnesium at an aluminium electrode leads to the formation of Al-Mg alloys, and the succeeding underpotential deposition of lithium on predeposited Al-Mg alloys leads to the formation of Al-Li-Mg alloys. Chronopotentiometric measurements indicated that the codeposition of Mg and Li occurs at current densities lower than -0.668 A cm-2 in LiCl-KCl-MgCl2 (8 wt pct) melts at an aluminium electrode. The chronoamperometric studies indicated that the onset potential for the codeposition of Mg and Li is -2.000 V, and the codeposition of Mg and Li at an aluminium electrode is formed into Al-Li-Mg alloys when the applied potentials are more negative than -2.000 V. X-ray diffraction and inductively coupled plasma analysis indicated that Al-Li-Mg alloys with different lithium and magnesium contents were prepared via potentiostatic and galvanostatic electrolysis. The microstructure of typical dual phases of the Al-Li-Mg alloy was characterized by an optical microscope and by scanning electron microscopy. The analysis of energy dispersive spectrometry showed that the elements of Al and Mg distribute homogeneously in the Al-Li-Mg alloy. The lithium and magnesium contents of Al-Li-Mg alloys can be controlled by MgCl2 concentrations and by electrolytic parameters.

  18. New type of magnetic tunnel junction based on spin filtering through a reduced symmetry oxide: FeCo|Mg3B2O6|FeCo.

    PubMed

    Stewart, Derek A

    2010-01-01

    Magnetic tunnel junctions with high-tunneling magnetoresistance values such as Fe|MgO|Fe capitalize on spin filtering in the oxide region based on the band symmetry of incident electrons. However, these structures rely on magnetic leads and oxide regions of the same cubic symmetry class. A new magnetic tunnel junction (FeCo|Mg(3)B(2)O(6)|FeCo) is presented that uses a reduced symmetry oxide region (orthorhombic) to provide spin filtering between the two cubic magnetic leads. Complex band structure analysis of Mg(3)B(2)O(6) based on density functional calculations shows that significant spin filtering could occur in this system. This new type of magnetic tunnel junction may have been fabricated already and can explain recent experimental studies of rf-sputtered FeCoB|MgO|FeCoB junctions where there is significant B diffusion into the MgO region. PMID:20017563

  19. 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.

  20. Dependency of tunneling magneto-resistance on Fe insertion-layer thickness in Co2Fe6B2/MgO-based magnetic tunneling junctions

    NASA Astrophysics Data System (ADS)

    Chae, Kyo-Suk; Park, Jea-Gun

    2015-04-01

    For Co2Fe6B2/MgO-based perpendicular magnetic tunneling junctions spin valves with [Co/Pd]n-synthetic-antiferromagnetic (SyAF) layers, the tunneling-magneto-resistance (TMR) ratio strongly depends on the nanoscale Fe insertion-layer thickness (tFe) between the Co2Fe6B2 pinned layer and MgO tunneling barrier. The TMR ratio rapidly increased as tFe increased up to 0.4 nm by improving the crystalline linearity of a MgO tunneling barrier and by suppressing the diffusion of Pd atoms from a [Co/Pd]n-SyAF. However, it abruptly decreased by further increasing tFe in transferring interfacial-perpendicular magnetic anisotropy into the IMA characteristic of the Co2Fe6B2 pinned layer. Thus, the TMR ratio peaked at tFe = 0.4 nm: i.e., 120% at 29 Ωμm2

  1. 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.

  2. Structural, morphological and interfacial characterization of Al-Mg/TiC composites

    SciTech Connect

    Contreras, A. . E-mail: acontrer@imp.mx; Angeles-Chavez, C.; Flores, O.; Perez, R.

    2007-08-15

    Morphological and structural characterization of Al-Mg/TiC composites obtained by infiltration process and wetting by the sessile drop technique were studied. Focusing at the interface, wetting of TiC substrates by molten Al-Mg-alloys at 900 deg. C was investigated. Electron probe microanalysis (EPMA) indicated that aluminum carbide (Al{sub 4}C{sub 3}) is formed at the interface and traces of TiAl{sub 3} in the wetting assemblies were detected. Scanning Electron Microscopy (SEM) observations show that TiC particles do not appear to be uniformly attacked to produce a continuous layer of Al{sub 4}C{sub 3} at the interface. Molten Al-Mg-alloys were infiltrated into TiC preforms with flowing argon at a temperature of 900 deg. C. In the composites no reaction phase was observed by SEM. Quantification of the Al phase in the composite was carried out by X-ray diffraction (XRD) and Rietveld analysis. Chemical mapping analyzed by SEM shows that the Al-Mg alloy surrounds TiC particles. In the composites with 20 wt.% of Mg the Al-Mg-{beta} phase was detected through XRD.

  3. 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.

  4. 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.

  5. Cap-Induced Magnetic Anisotropy in Ultra-thin Fe/MgO(001) Films

    NASA Astrophysics Data System (ADS)

    Brown-Heft, Tobias; Pendharkar, Mihir; Lee, Elizabeth; Palmstrom, Chris

    Magnetic anisotropy plays an important role in the design of spintronic devices. Perpendicular magnetic anisotropy (PMA) is preferred for magnetic tunnel junctions because the resulting energy barrier between magnetization states can be very high and this allows enhanced device scalability suitable for magnetic random access memory applications. Interface induced anisotropy is often used to control magnetic easy axes. For example, the Fe/MgO(001) system has been predicted to exhibit PMA in the ultrathin Fe limit. We have used in-situ magneto optic Kerr effect and ex-situ SQUID to study the changes in anisotropy constants between bare Fe/MgO(001) films and those capped with MgO, Pt, and Ta. In some cases in-plane anisotropy terms reverse sign after capping. We also observe transitions from superparamagnetic to ferromagnetic behavior induced by capping layers. Perpendicular anisotropy is observed for Pt/Fe/MgO(001) films after annealing to 300°C. These effects are characterized and incorporated into a magnetic simulation that accurately reproduces the behavior of the films. This work was supported in part by the Semiconductor Research Corporation programs (1) MSR-Intel, and (2) C-SPIN.

  6. Mechanical and wear properties of Al-Al3Mg2 nanocomposites prepared by mechanical milling and hot pressing

    NASA Astrophysics Data System (ADS)

    Zolriasatein, A.; Khosroshahi, R. A.; Emamy, M.; Nemati, N.

    2013-03-01

    β-Al3Mg2 intermetallic was used as a reinforcing agent to improve the mechanical properties of an aluminum matrix. Different amounts of Al3Mg2 nanoparticles (ranging from 0wt% to 20wt%) were milled with aluminum powders in a planetary ball mill for 10 h. Consolidation was conducted by uniaxial pressing at 400°C under a pressure of 600 MPa for 2 h. Microstructural characterization confirms the uniform distribution of Al3Mg2 nanoparticles within the matrix. The effects of nano-sized Al3Mg2 content on the wear and mechanical properties of the composites were also investigated. The results show that as the Al3Mg2 content increases to higher levels, the hardness, compressive strength, and wear resistance of the nanocomposites increase significantly, whereas the relative density and ductility decrease. Scanning electron microscopy (SEM) analysis of worn surfaces reveals that a transition in wear mechanisms occurs from delamination to abrasive wear by the addition of Al3Mg2 nanoparticles to the matrix.

  7. Isotopic fractionation of Mg 2+(aq), Ca 2+(aq), and Fe 2+(aq) with carbonate minerals

    NASA Astrophysics Data System (ADS)

    Rustad, James R.; Casey, William H.; Yin, Qing-Zhu; Bylaska, Eric J.; Felmy, Andrew R.; Bogatko, Stuart A.; Jackson, Virgil E.; Dixon, David A.

    2010-11-01

    Density-functional electronic structure calculations are used to compute the equilibrium constants 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 10 3ln ( K) at 25 °C, of -5.3, -1.1, and +1.2 for 26Mg/ 24Mg exchange between calcite (CaCO 3), magnesite (MgCO 3), and dolomite (Ca 0.5Mg 0.5CO 3), respectively, and Mg 2+(aq), with positive values indicating enrichment of the heavy isotope in the mineral phase. For 44Ca/ 40Ca exchange between calcite and Ca 2+(aq) at 25 °C, the calculations predict values of +1.5 for Ca 2+(aq) in 6-fold coordination and +4.1 for Ca 2+(aq) in 7-fold coordination. We find that the reduced partition function ratios can be reliably computed from systems as small as M(CO)610- and M(HO)62+ embedded in a set of fixed atoms representing the second-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 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 Fe 3+-hematite and Fe 2+-siderite fractionations arise from an insufficiently accurate reduced partition function ratio for the Fe 3+(aq) and Fe 2+(aq) species.

  8. 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.

  9. Structure and photoluminescence of Mg-Al-Eu ternary hydrotalcite-like layered double hydroxides

    SciTech Connect

    Chen Yufeng; Li Fei; Zhou Songhua; Wei Junchao; Dai Yanfeng; Chen Yiwang

    2010-09-15

    A series of Mg-Al-Eu ternary hydrotalcite-like layered double hydroxides (LDHs), with Eu/Al atomic ratios of {approx}0.06 and Mg/(Al+Eu) atomic ratios ranging from 1.3 to 4.0, were synthesized by a coprecipitation method. The Mg-Al-Eu ternary LDHs were investigated by various techniques. X-ray diffraction (XRD) results indicated that the crystallinity of the ternary LDHs was gradually improved with the increase of Mg{sup 2+}/(Al{sup 3+}+Eu{sup 3+}) molar ratio from 1.3/1 to 4/1, and all the samples were a single phase corresponding to LDH. The photoluminescent (PL) spectra of the ternary Mg-Al-Eu LDHs were described by the well-known {sup 5}D{sub 0}-{sup 7}F{sub J} transition (J=1, 2, 3, 4) of Eu{sup 3+} ions with the strongest emission for J=2, suggesting that the host LDH was favorable to the emissions of Eu{sup 3+} ions. The asymmetry parameter (R) relevant to {sup 5}D{sub 0}-{sup 7}F{sub J} transition (J=1, 2) dependant of the atomic ratios of Mg{sup 2+}/(Al{sup 3+}+Eu{sup 3+}) was discussed, and was consistent with the result of XRD. - Graphical abstract: A series of Mg-Al-Eu ternary hydrotalcite-like layered double hydroxides (LDHs), with Mg/(Al+Eu) atomic ratios ranging from 1.3/1, 2/1 3/1 to 4/1, were synthesized by a coprecipitation method. The photoluminescent spectra of the Mg-Al-Eu ternary LDHs are described by the well-known {sup 5}D{sub 0}-{sup 7}F{sub J} transition (J=1, 2, 3, 4) of Eu{sup 3+} ions with the strongest emission for J=2.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. Million year cycles in the Fe, Mg and Ni records of a ferromanganese crust from the equatorial Indian Ocean

    NASA Astrophysics Data System (ADS)

    Banerjee, R.; Gupta, S. M.; Miura, H.

    2008-12-01

    In search of long term productivity signals, a high resolution geochemical study was undertaken by using the life sustaining iron and magnesium contents in a slowly accreting 26 mm thick hydrogenous Fe-Mn crust representing around 12 Million years (Ma) record from the equatorial Indian Ocean. We analyzed Fe, Mg, Ni, Co, and other trace metals by using electron probe micro-analyzer at 100 micron interval. The geochemical data was averaged at every 1 mm interval and subjected to statistical analyses. The crust was dated using standard cobalt-chronometry (Manheim and Lane-Bostwick, 1998). Mixed age-depth model (Heegaard et al., 2005) was applied to ascertain the error limits in the computed ages for each millimeter of the crust. Thereafter, the Red-fit (Schulz and Mudelsee, 2002) and multi-taper (Thompson, 1990) spectral analyses of Fe, Mg and Ni revealed the existence of the significant (>90%) cycles at around 3, 1.5, and 1.2 Ma. We surmise that Fe and Mg cycles represented the changes in oceanic productivity as these metals are essentially used in sustaining the oceanic phyto- and zoo-plankton productivity in the surface water. The Fe/Ni ratio, which is attributed to meteoritic dust influx (Johnson, 2001), also revealed the similar cycles suggesting a possibility of Ni input from the meteoritic dust in the past. We compared the geochemical time- series data with the Earth's orbital eccentricity and summer solar insolation (Berger, 1979) at the equator for the last 10 million years. The Redfit and multi-taper analyses of the eccentricity and the insolation also resulted similar cycles at around 1.5 and 1.2 Ma. Therefore, we surmise that the Fe, Mg, and Ni cycles at 1.5, and 1.2 Ma could be result of the geochemical response to the Earth's eccentricity related solar insolation changes. Earlier studies reported cycles due to eccentricity (0.4, 0.126, 0.95 Ma), tilt (0.041 Ma) and precession (0.023 Ma) in Indian Ocean, whereas we report here 3, 1.5 and 1.2 Ma supra

  15. Energy-filtered plasmon images of MgAl{sub 2}O{sub 4} implanted with Al{sup +} and Mg{sup +} ions

    SciTech Connect

    Evans, N.D.; Bentley, J.; Zinkle, S.J.

    1995-06-01

    Magnesium aluminate spinel (MgAl{sub 2}O{sub 4}) is a candidate material for specialized applications in proposed fusion reactors, and previously, has been irradiated with Al{sup +} or Mg{sup +} ions to assess the effects of high-dose irradiation. Electron energy-loss spectrometry (EELS) has been used to confirm the identity of metallic aluminum colloids located in the ion-implanted region of the spinel because electron diffraction experiments were inconclusive for phase identification. In the present study, energy-filtered plasmon images of the ion-implanted region have been obtained to reveal this colloid distribution.

  16. 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

  17. 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

  18. 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.

  19. Identification of an incommensurate FeAl{sub 2} overlayer on FeAl(110) using x-ray diffraction and reflectivity

    SciTech Connect

    Baddorf, A.P.; Chandavarkar, S.S.

    1995-06-30

    FeAl, like NiAl, crystallizes in the CsCl structure. Consequently the (110) planes contain equal amounts of Fe and Al distributed as interlocking rectangles. Unlike the NiAI(110) surface, which retains the (1{times}l) in-plane symmetry of the bulk, FeAl(l10) reconstructs to form an ordered, incommensurate overlayer. The reconstructed layer introduces x-ray diffraction rods at half-order positions along the [1{bar 1}0] direction, and displaced {plus_minus}0.2905 from integer positions along the [001] direction. Peak widths reveal excellent long range order. Specular reflectivity measurements above and below the Fe K{alpha} edge can be reproduced using a model containing a single reconstructed overlayer with an Fe:Al ratio of 1:2, consistent with FeA{sub I}2.

  20. Precise lattice location of substitutional and interstitial Mg in AlN

    SciTech Connect

    Amorim, L. M.; Pereira, L. M. C.; Decoster, S.; Temst, K.; Vantomme, A.; Wahl, U.; Correia, J. G.; Silva, D. J.; Silva, M. R. da; Gottberg, A.

    2013-12-23

    The lattice site location of radioactive {sup 27}Mg implanted in AlN was determined by means of emission channeling. The majority of the {sup 27}Mg was found to substitute for Al, yet significant fractions (up to 33%) were also identified close to the octahedral interstitial site. The activation energy for interstitial Mg diffusion is estimated to be between 1.1 eV and 1.7 eV. Substitutional Mg is shown to occupy ideal Al sites within a 0.1 Å experimental uncertainty. We discuss the absence of significant displacements from ideal Al sites, in the context of the current debate, on Mg doped nitride semiconductors.

  1. 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.

  2. High spatial resolution Mg/Al maps of the western Crisium and Sulpicius Gallus regions

    NASA Technical Reports Server (NTRS)

    Schonfeld, E.

    1982-01-01

    High spatial resolution Mg/Al ratio maps of the western Crisium and Sulpicius Gallus regions of the moon are presented. The data is from the X-ray fluorescence experiment and the image enhancement technique in the Laplacian subtraction method using a special least-squares version of the Laplacian to reduce noise amplification. In the highlands region west of Mare Crisium several relatively small patches of smooth material have high local Mg/Al ratio similar to values found in mare sites, suggesting volcanism in the highlands. In the same highland region there were other smooth areas with no high Mg/Al local values and they are probably Cayley Formation material produced by impact mass wasting. The Sulpicius Gallus region has variable Mg/Al ratios. In this region there are several high Mg/Al ratio spots, two of which occur at the highland-mare interface. Another high Mg/Al ratio area corresponds to the Sulpicius Gallus Rima I region. The high Mg/Al ratio material in the Sulpicius Gallus region is probably pyroclastic.

  3. [Preparation and optical properties of MgAl2O4/Ce:YAG transparent ceramics].

    PubMed

    He, Long-Fei; Fan, Guang-Han; Lei, Mu-Yun; Lou, Zai-Liang; Chen, Zhi-Wu; Xiao, Yao; Zheng, Shu-Wen; Zhang, Tao

    2013-05-01

    High-purity ultrafine MgAl2O4 powder was synthesized by metal-alkoxide method and calcining for 2-4 h. And then MgAl2O4/Ce:YAG transparent ceramics were fabricated by hot-pressed sintering and hot isostatic pressed sintering technique with YAG:Ce powder and MgAl2O4 powder. The transparent ceramics were characterized by XRD, SEM, EDS and fluorescence spectrometer, respectively. The results show that the crystal phase of the transparent ceramic was composed of MgAl2O4 and YAG,and the YAG phase dispersed well in the matrix of MgAl2O4. The excitation spectra had a weak band at 345 nm and a strong band at 475 nm. The broad emission peaks at about 533 nm were attributed to 5d-->4f transition of Ce3+ ions. Decay curves for the fluorescence of MgAl2O4/Ce:YAG transparent ceramic test show that the lifetime of the Ce:YAG glass ceramic was 59.74 ns. All results show that MgAl2O4/Ce:YAG transparent ceramic may be a promising fluorescent material for white LED applications. PMID:23905313

  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. Epitaxial Fe3Pt/FePt nanocomposites on MgO and SrTiO3

    NASA Astrophysics Data System (ADS)

    Casoli, F.; Lupo, P.; Nasi, L.; Cabassi, R.; Fabbrici, S.; Bolzoni, F.; Ranzieri, P.; Albertini, F.

    2015-02-01

    We have exploited the pseudomorphic growth of the magnetically soft Fe3Pt phase on top of L10-FePt to obtain fully epitaxial soft/hard nanocomposites on both MgO(100) and SrTiO3(100). The magnetic properties of this new nanocomposite system, driven by the soft/hard exchange-coupling, can be tailored by varying soft phase thickness, soft phase magnetic anisotropy and substrate. Coercivity is strongly reduced by the addition of the soft phase, a reduction which is definitely affected by the nominal composition of the soft phase and by the substrate choice; similarly is the magnetic phase diagram of the composite system. Coercive field decreases down to 21% of the hard layer value for Fe3Pt(5 nm)/FePt(3.55 nm) nanocomposites on SrTiO3; this maximum coercivity reduction was obtained with a nominal atomic content of Fe in the soft phase of 80%.

  6. Modeling of the solubilities of NiO/NiAl2O4 and FeO/FeAl2O4 in cryolite melts at 1300 K

    NASA Astrophysics Data System (ADS)

    Zhang, Yunshu; Wu, Xiaoxia; Rapp, Robert A.

    2004-02-01

    Experiments to measure the solubilities of NiO/NiAl2O4 and FeO/FeAl2O4 were performed, and the results confirmed existing literature values. The solubilities of NiAl2O4 and FeAl2O4 in Al2O3-saturated cryolite melts at 1300 K were modeled thermodynamically in terms of the Ni-containing complexes Na2NiF4 and Na4NiF6, and the Fe-containing solutes FeF2, Na2FeF4, and Na4FeF6. The experimental solubility data were fitted to multiple simultaneous equilibria. Equilibrium constants and ΔG f 0 values for the formation reactions of the these solutes were thereby estimated. The solubilities of NiO/NiAl2O4 and FeO/FeAl2O4 and solute distributions in Al2O3-undersaturated cryolite melts were calculated for a number of melt compositions from the present model. The existence of several competitive solute species is inherent to highly buffered ionic cryolite solutions where the traditional log-log methodology had previously failed to identify dominant single solutes. In such solutions, individual solutes of oxides are not likely to dominate over a wide composition range so that a more global modeling is required. The principal solute species identified in the present study exhibit reasonable three-dimensional (3-D) anion geometries.

  7. 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).

  8. Erosion behavior of Fe-Al intermetallic alloys

    SciTech Connect

    Kim, Y.S.; Song, J.H.; Chang, Y.W.

    1997-04-01

    The Fe-rich Fe-Al intermetallics have generated some interest, especially during the last decade, due to their excellent resistance for oxidation and sulfidation, high specific strength, and low material cost. The aluminide is therefore considered as one of the promising candidates for high-temperature structural materials in a corrosive atmosphere. Research effort has been focused mainly on process, development, and enhancement of room-temperature ductility together with the characterization of physical properties such as mechanical properties, oxidation, corrosion, and abrasive wear behavior. However, there have been only a few works reported to date in regard to the erosion characteristics of the alloy, one of the most important material property of this ordered intermetallic alloy for the use in a fossil-fuel plant. In this study, the solid-particle erosion behavior of the Fe-Al intermetallic alloys containing the various aluminum contents ranging from 25 to 30 at.% has been investigated to clarify the effect of aluminum content and different ordered structures, viz. DO{sub 3} and B2, on the erosion behavior. An attempt has been made to correlate the erosion behavior of these intermetallics to their mechanical properties by carrying out tensile tests together with SEM observation of the eroded surfaces.

  9. 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.

  10. 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.

  11. 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.

  12. Influence of ion beam assisted deposition parameters on the growth of MgO and CoFeB

    SciTech Connect

    Ferreira, Ricardo; Freitas, Paulo P.; Petrova, Rumyana; McVitie, Stephen

    2012-04-01

    The effect of the kinetic parameters of an assistance ion beam on the crystallization of ion beam deposited MgO was investigated. It is shown that the crystallization of MgO in the as-deposited state is strongly dependent on the assistance beam parameters. Furthermore, two deposition regimes corresponding to different ranges of the assistance beam energy are found. XRD and TEM studies of CoFeB/MgO/CoFeB with MgO deposited in the two regimes show that CoFeB crystallization is favored when low energy assist beams are used, despite no differences being found in the MgO.

  13. Equilibrium point defects in intermetallics with the [ital B]2 structure: NiAl and FeAl

    SciTech Connect

    Fu, C.L.; Ye, Y.; Yoo, M.H. ); Ho, K.M. )

    1993-09-01

    Equilibrium point defects and their relation to the contrasting mechanical behavior of NiAl and FeAl are investigated. For NiAl, the defect structure is dominated by two types of defects---monovacancies on the Ni sites and substitutional antisite defects on the Al sites. The defect structure of FeAl differs from that of NiAl in the occurrence of antisite defects at the transition-metal sites for Al-rich alloys and the tendency for vacancy clustering. The strong ordering (and brittleness) of NiAl is attributed mainly to the difference in atomic size between constituent atoms.

  14. 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.

  15. 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.

  16. 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.

  17. Improved Wear Resistance of Al-Mg Alloy with SiC and Al2O3 Particle Reinforcement

    NASA Astrophysics Data System (ADS)

    Mehedi, Md. A.; Bhadhon, K. M. H.; Haque, M. N.

    2016-01-01

    Al-3.73Mg alloy was reinforced with a different ratio of SiC and Al2O3 particulate mixtures, and their corresponding wear properties were investigated by pin-on-disk method. The investigation revealed that the mass loss of the hybrid composite at different loads and sliding velocities reduced with the increase of the SiC volume. Only 6% particulate reinforcement in the Al-Mg matrix was enough to reduce the wear of the surface by one-fourth. The wear mechanism was also investigated by examining the worn surface with a scanning electron microscope.

  18. Strain effect on magnetocrystalline anisotropy of 5 d TM/Fe and TM/Fe/MgO(001) (TM =Ta, Ir, Pt, Au): A first principles study

    NASA Astrophysics Data System (ADS)

    Taivansaikhan, Purev; Odkhuu, Dorj; Rhim, Sung-Hyon; Hong, Soon Cheol

    2015-03-01

    Strain effect on magnetization and magnetocrystalline anisotropy (MCA) of TM/Fe(001) [TM =Ta, Ir, Pt and Au] with and without MgO(001) substrate has been investigated using first-principles calculations. It is found that perpendicular MCA of Pt/Fe(001) changes to in-plane MCA in the presence of MgO substrate, where lattice is extended by 3.8% with respect to that without MgO. For Ta/Fe(001) and Au/Fe(001), PMCA is significantly enhanced by the MgO substrate, whereas MCA of Ir/Fe(001) remains in-plane. Furthermore, thickness dependence of MCA on both the TM and Fe layers will be also discussed. Supported by Basic Research Program (2010-0008842) and Research Centers Program (2009-0093818) through National Research Foundation of Korea.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Back transformation and oxidation of (Mg, Fe)2SiO4 spinels at high temperatures

    NASA Astrophysics Data System (ADS)

    Ming, L. C.; Kim, Y. H.; Manghnani, M. H.; Usha-Devi, S.; Ito, E.; Xie, H.-S.

    1991-10-01

    Based on the in situ and temperature-quench X-ray measurements, the back transformation in the (Mg, Fe)2SiO4-spinels has been characterized in terms of the transformation temperature ( T r ),mechanism and kinetics of the transformation, and of the end product(s), with specific emphasis on the effect of oxygen on this transformation. The in situ measurements were conducted to 900° C in vacuum (10-4 to 10-5 torr) and to 600° C in air using synchrotron radiation (SR) at Stanford Synchrotron Radiation Laboratory (SSRL). In the quench-type measurements, samples were heated in air to 1100° C, quenched and examined at ambient conditions using the conventional X-ray diffraction facilities. Important results are (1) in vacuum, all the spinels convert back into the olivine phase, with their T r decreasing with increasing iron content; (2) the spinel → olivine back transformation is a nucleation and growth type of transformation and can be described quantitatively using the Avrami equation; (3) in air, the (Mg, Fe)2SiO4-spinels with 0.2 mole fraction Fe or more are all oxidized, and the composition and phase of the end products depend upon the temperature and the starting composition; and (4) the oxidation of the iron-rich (Mg, Fe)2SiO4-spinels in air occurs at ˜350 400° C, which is significantly lower than its T r (˜ 300° C) in vacuum.

  4. 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).

  5. Disproportionation of (Mg,Fe)SiO3 Perovskite and its Implications to the Deep Earth

    NASA Astrophysics Data System (ADS)

    Zhang, L.; Meng, Y.; Yang, W.; Wang, L.; Mao, W. L.; Zeng, Q. C.; Jeong, J. S.; Wagner, A. J.; Mkhoyan, K. A.; Liu, W.; Xu, R.; Mao, H. K.

    2014-12-01

    Models of the Earth's deep interior have been built upon the basic assumption that the lower mantle down to the top of the D" layer mainly consists of orthorhombic perovskite (pv) with nominally 10 mol% Fe. However, seismic observations show enigmatic features in the deep lower mantle, such as, the sharp boundary on the top of the D″ layer, the anticorrelations between VS and VP, the seismic anisotropy, and the existence of large low-shear-velocity provinces. The mineralogical constitution of the Earth's mantle is fundamental for understanding the geophysical and geochemical properties of this region. Our recent study using laser-heated diamond anvil cell technology coupled with synchrotron x-ray diffraction in-situ at high pressure-temperature and TEM studies of the quenched sample has demonstrated the disproportionation reaction of (Mg,Fe)SiO3 pv to a nearly Fe-free pv and an Fe-rich H-phase with a previously unknown hexagonal structure at 95 to 101 GPa and 2200 to 2400 K, thus fundamentally changing the geochemistry and geophysics of the bottom half of the lower mantle. We suggest that (Mg,Fe)SiO3 pv may not be the major silicate throughout the lower mantle down to the top of the D" layer. Instead, interpretations for key enigmatic features in the deep lower mantle require the knowledge of the three-phase P-T-x relationship of pv, ppv, and the H-phase.

  6. Synthesis of MgO nanoparticle loaded mesoporous Al2O3 and its defluoridation study

    NASA Astrophysics Data System (ADS)

    Dayananda, Desagani; Sarva, Venkateswara R.; Prasad, Sivankutty V.; Arunachalam, Jayaraman; Parameswaran, Padmanabhan; Ghosh, Narendra N.

    2015-02-01

    MgO nanoparticle loaded mesoporous alumina has been synthesized using a simple aqueous solution based cost effective method for removal of fluoride from water. Wide angle powder X-ray diffraction, nitrogen adsorption desorption analysis, transmission electron microscopy techniques and energy dispersive X-ray spectroscopy were used to characterize the synthesized adsorbents. Synthesized adsorbents possess high surface area with mesoporous structure. The adsorbents have been thoroughly investigated for the adsorption of F- using batch adsorption method. MgO nanoparticle loading on mesoporous Al2O3 enhances the F- adsorption capacity of Al2O3 from 56% to 90% (initial F- concentration = 10 mg L-1). Kinetic study revealed that adsorption kinetics follows the pseudo-second order model, suggesting the chemisorption mechanism. The F- adsorption isotherm data was explained by both Langmuir and Freundlich model. The maximum adsorption capacity of 40MgO@Al2O3 was 37.35 mg g-1. It was also observed that, when the solutions having F- concentration of 5 mg L-1 and 10 mg L-1 was treated with 40MgO@Al2O3, the F- concentration in treated water became <1 mg L-1, which is well below the recommendation of WHO.

  7. Reflection polarizers for the vacuum ultraviolet using Al + MgF2 mirrors and an MgF2 plate

    NASA Technical Reports Server (NTRS)

    Hass, G.; Hunter, W. R.

    1978-01-01

    Consideration is given to the design and operation of a three-mirror reflecting polarizer where one of the reflecting surfaces is an MgF2 plate, the other surfaces are Al + MgF2 coatings, and one reflection occurs at or near the true Brewster angle. It is found that the polarizer is most efficient in the 1200-2000 A wavelength region, and that by optimum selection of the angle of incidence on the MgF2 plate, polarization values of 100 and over are yielded from 900 to 3000 A. The polarizer may be used at wavelengths as short as 500 A, although it is observed that at such wavelengths the polarization value decreases to about 10. It is noted that all reflecting polarizers operating in the vacuum ultraviolet wavelength may manifest changing characteristics as their mirrors become contaminated, and that polarization must therefore be occasionally remeasured.

  8. 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.

  9. MOKE Study of Fe/Co/Al Multilayers

    SciTech Connect

    Jani, Snehal; Lakshmi, N.; Venugopalan, K.; Rajput, Parasmani; Zajaoc, M.; Rueffer, R.; Reddy, V. R.; Gupta, Ajay

    2011-07-15

    The multilayer system (MLS)-[{sup 57}Fe{sub 25}A/Co{sub 11}A/Al{sub 17}A]x20 has been deposited by Ion beam sputtering (IBS) technique. The MLS has been annealed at 700 deg. C for 1 h. Overall composition of as deposited and annealed MLS have been characterized by EDX and magnetic properties have been studied through angular dependent magneto optic Kerr effect (MOKE) hysteresis curves. The study shows that the as-deposited MLS has excellent soft magnetic properties coupled with perpendicular magnetic isotropy which is destroyed on annealing.

  10. 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.

  11. Annealing of cold-rolled Fe-40Al single crystals

    SciTech Connect

    Yang, Y.; Baker, I.

    1997-12-31

    Single crystals of Fe-40Al were cold-rolled to plastic strains in the range 5% to 48%. Discs cut from the rolled crystals at different rolling strains were heated at 10 K/min in a differential scanning calorimeter from room temperature to 973 K. Three exothermic peaks were observed in the temperature ranges of 440--550 K, 610--650 K, and 860--930 K, all the peaks shifting to lower temperatures with increasing strain. The origins of these peaks are discussed in terms of the disorder and vacancies introduced during rolling.

  12. Bifunctional Modification of Graphitic Carbon Nitride with MgFe2O4 for Enhanced Photocatalytic Hydrogen Generation.

    PubMed

    Chen, Jie; Zhao, Daming; Diao, Zhidan; Wang, Miao; Guo, Liejin; Shen, Shaohua

    2015-08-26

    To gain high photocatalytic activity for hydrogen evolution, both charge separation efficiency and surface reaction kinetics must be improved, and together would be even better. In this study, the visible light photocatalytic hydrogen production activity of graphitic carbon nitride (g-C3N4) was greatly enhanced with MgFe2O4 modification. It was demonstrated that MgFe2O4 could not only extract photoinduced holes from g-C3N4, leading to efficient charge carrier separation at the g-C3N4/MgFe2O4 interface, but also act as an oxidative catalyst accelerating the oxidation reaction kinetics at g-C3N4 surface. This dual function of MgFe2O4 thus contributed to the great improvement (up to three-fold) in photocatalytic activity for hydrogen generation over g-C3N4/MgFe2O4 as compared to pristine g-C3N4, after loading Pt by photoreduction method. It was revealed that in the Pt/g-C3N4/MgFe2O4 system, the photoinduced electrons and holes were entrapped by Pt and MgFe2O4, respectively, giving rise to the promoted charge separation; moreover, as evidenced by electrochemical analysis, the electrocatalysis effect of MgFe2O4 benefited the oxidation reaction at g-C3N4 surface. PMID:26237590

  13. 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.

  14. 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.

  15. Microstructural stability and creep properties of die casting Mg-4Al-4RE magnesium alloy

    SciTech Connect

    Rzychon, Tomasz; Kielbus, Andrzej; Cwajna, Jan; Mizera, Jaroslaw

    2009-10-15

    The AE44 (Mg-4Al-4RE) alloy was prepared by a hot-chamber die casting method. The microstructure, microstructural stability and creep properties at 175 deg. C were investigated. The microstructure was analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and the Rietveld method. The results show that die cast AE44 magnesium alloy consists of {alpha}-Mg, Al{sub 11}RE{sub 3}, Al{sub 2}RE and Al{sub 2.12}RE{sub 0.88} phases. The Al{sub 11}RE{sub 3} phase is thermally stable at 175 deg. C whereas the metastable Al{sub 2.12}RE{sub 0.88} phase undergoes a transition into the equilibrium Al{sub 2}RE phase. The alloy investigated is characterized by good creep properties at temperatures of 175 deg. C and 200 {sup o}C.

  16. 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.

  17. 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.

  18. Reduction in the Number of Mg Acceptors with Al Concentration in Al x Ga1- x N

    NASA Astrophysics Data System (ADS)

    Sunay, U. R.; Zvanut, M. E.; Allerman, A. A.

    2015-11-01

    High hole concentrations in Al x Ga1- x N become increasingly difficult to obtain as the Al mole fraction increases. The problem is believed to be related to compensation, extended defects, and the band gap of the alloy. Whereas electrical measurements are commonly used to measure hole density, in this work we used electron paramagnetic resonance (EPR) spectroscopy to investigate a defect related to the neutral Mg acceptor. The amount and symmetry of neutral Mg in MOCVD-grown Al x Ga1- x N with x = 0 to 0.28 was monitored for films with different dislocation densities and surface conditions. EPR measurements indicated that the amount of neutral Mg decreased by 60% in 900°C-annealed Al x Ga1- x N films for x = 0.18 and 0.28 as compared with x = 0.00 and 0.08. A decrease in the angular dependence of the EPR signal accompanied the increased x, suggesting a change in the local environment of the Mg. Neither dislocation density nor annealing conditions contribute to the reduced amount of neutral Mg in samples with the higher Al concentration. Rather, compensation is the simplest explanation of the observations, because a donor could both reduce the number of neutral acceptors and cause the variation in the angular dependence.

  19. 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.

  20. Experimental investigation of T =1 analog states of 26Al and 26Mg

    NASA Astrophysics Data System (ADS)

    Srivastava, Vishal; Bhattacharya, C.; Rana, T. K.; Manna, S.; Kundu, S.; Bhattacharya, S.; Banerjee, K.; Roy, P.; Pandey, R.; Mukherjee, G.; Ghosh, T. K.; Meena, J. K.; Roy, T.; Chaudhuri, A.; Sinha, M.; Saha, A. K.; Asgar, Md. A.; Dey, A.; Roy, Subinit; Shaikh, Md. M.

    2016-04-01

    The even-even nucleus 26Mg has been studied through the reaction 27Al(d ,3He) at 25 MeV beam energy. The spectroscopic factors of the lowest (T =1 ) states of 26Mg have been extracted using the zero-range distorted wave Born approximation. These spectroscopic factors are compared with those of T =1 analog states in 26Al and found to be in good agreement.

  1. Multilayer FeRh/MgO: controllable magnetocrystalline anisotropy for an antiferromagnetic system

    NASA Astrophysics Data System (ADS)

    Zheng, Guohui; Dorj, Odkhuu; Ke, Sanhuang; Ramesh, Rammoorthy; Miao, Maosheng; Kioussis, Nickolas

    2015-03-01

    Controlling the magnetocrystalline anisotropy (MCA) of ferromagnetic (FM) thin films by tunable strain and electric field has been pursued as an effective method of achieving low-power and highly scalable memory. Comparing with FM materials, AFM are much less sensitive to external magnetic field, a substantial advantage for memory devices. Inspired by recent work on AFM memory resistors based on FeRh, we carried out a systematic first principles study of the MCA of multi-layer FeRh, either stand alone, or combined with MgO layers. FeRh is a unique material that undergoes a transition from AFM (type-II) to FM at elevated temperature of 370 K. Our calculations for thin films of FeRh from 5-15 atomic layers reveal that AFM is always the most stable configuration for Fe terminated films; while for Rh terminated films, there is a transition from FM to a configuration featured AFM at the center layers and FM at the surface layers (reconstructed). While applying the spin-orbit interactions (SOI) for the valence electrons, we found Fe-terminated films exhibit a relatively small MCA that varies and may change sign with film thickness, substrate and strain, providing a possibility of spin reorientation via the control of strain and electric field. The k-resolved MCA values reveals that the region around Gamma point adds the major contribution to the MCA.

  2. Importance of doping and frustration in itinerant Fe-doped Cr2Al

    DOE PAGESBeta

    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

  3. 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.

  4. 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.

  5. 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.

    2016-03-01

    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.

  6. Phase Evolution and Properties of Al2CrFeNiMo x High-Entropy Alloys Coatings by Laser Cladding

    NASA Astrophysics Data System (ADS)

    Wu, Wei; Jiang, Li; Jiang, Hui; Pan, Xuemin; Cao, Zhiqiang; Deng, Dewei; Wang, Tongmin; Li, Tingju

    2015-10-01

    A series of Al2CrFeNiMo x ( x = 0 to 2.0 at.%) high-entropy alloys coatings was synthesized on stainless steel by laser cladding. The effect of Mo content on the microstructures and mechanical properties of Al2CrFeNiMo x coatings was studied. The results show that the laser clad layer consists of the cladding zone, bonding zone, and heat-affected zone. The Al2CrFeNiMo x coatings are composed of two simple body-center cubic phases and the cladding zone is mainly composed of equiaxed grains. When the content of Mo reaches 2 at.%, a eutectic structure is found in the interdendritic regions. The surface microhardness of the Al2CrFeNiMo2 coating is 678 HV, which is about three times higher than that of the substrate (243 HV). Compared with stainless steel, the wear resistance of the coatings has been improved greatly. The wear mass loss of the Al2CrFeNiMo alloy is 9.8 mg, which is much less than that of the substrate (18.9 mg) and its wear scar width is the lowest among the Al2CrFeNiMo x coatings, indicating that the wear resistance of the Al2CrFeNiMo is the best.

  7. 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.

  8. 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.

  9. Optimized immobilization of transketolase from E. coli in MgAl-layered double hydroxides.

    PubMed

    Touisni, Nadia; Charmantray, Franck; Helaine, Virgil; Forano, Claude; Hecquet, Laurence; Mousty, Christine

    2013-12-01

    Immobilization of TK from Escherichia coli (TKec) on MgAl-NO3 layered double hydroxides (LDH) was carried out by two processes: adsorption and coprecipitation. As a comparison, the adsorption method was realized either at pH 7.5 in buffered solutions (MOPS and Gly-Gly) or in pure water. For the coprecipitation method, the formation of the inorganic LDH support was realized directly in the presence of TKec solubilized in Gly-Gly. The prepared biohybrids, called respectively TKec@LDHads and TKec@LDHcop, were characterized by powder X-ray diffraction, FTIR spectroscopy in comparison with TKec free reference products, i.e. MgAl-NO3, MgAl-Gly-Gly. The enzymatic activities of the various TKec@LDH biohybrids as well as their stabilities over time were investigated by UV-vis assay. A maximum of activity (12 U/mg of solid) was reached for TKec@MgAl-Gly-Gly biohybrid prepared by coprecipitation. Finally, thin films were prepared through a one-step deposition on a polished support. The enzymatic activity of the resulting TKec@MgAl-Gly-Glycop film was tested over four recycling processes with a reproducible activity of 2.7 U/mg cm(2). PMID:24055860

  10. Luminescence studies on SrMgAl 10O 17:Eu, Dy phosphor crystals

    NASA Astrophysics Data System (ADS)

    Wanjun, Tang; Donghua, Chen; Ming, Wu

    2009-02-01

    Using urea as fuel, SrMgAl 10O 17:Eu, Dy phosphor was prepared by a combustion method. Its luminescence properties under ultraviolet (UV) excitation were investigated. Pure SrMgAl 10O 17 phase was formed by urea-nitrate solution combustion synthesis at 550 °C. The results indicated that the emission spectra of SrMgAl 10O 17:Eu, Dy has one main peak at 460 nm and one shoulder peak near 516 nm, which are ascribed to two different types of luminescent Eu 2+ centers existing in the SrMgAl 10O 17 matrix crystal. The blue luminescence emission of SrMgAl 10O 17:Eu phosphors was improved under UV excitation by codoping Dy 3+ ions. The SrMgAl 10O 17:Eu phosphors showed green afterglow ( λ=516 nm) when Dy 3+ ions were doped. Dy 3+ ions not only successfully play the role of sensitizer for energy transfer in the system, but also act as trap levels and capture the free holes in the spinel blocks.

  11. 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

  12. Mesoporous mixed metal oxides derived from P123-templated Mg-Al layered double hydroxides

    SciTech Connect

    Wang Jun; Zhou Jideng; Li Zhanshuang; He Yang; Lin Shuangshuang; Liu Qi; Zhang Milin; Jiang Zhaohua

    2010-11-15

    We report the preparation of mesoporous mixed metal oxides (MMOs) through a soft template method. Different amounts of P123 were used as structure directing agent to synthesize P123-templated Mg-Al layered double hydroxides (LDHs). After calcination of as-synthesized LDHs at 500 {sup o}C, the ordered mesopores were obtained by removal of P123. The mesoporous Mg-Al MMOs fabricated by using 2 wt% P123 exhibited a high specific surface area of 108.1 m{sup 2}/g, and wide distribution of pore size (2-18 nm). An investigation of the 'memory effect' of the mesoporous MMOs revealed that they were successfully reconstructed to ibuprofen intercalated LDHs having different gallery heights, which indicated different intercalation capacities. Due to their mesoporosity these unique MMOs have particular potential as drug or catalyst carriers. - Graphical abstract: Ordered mesoporous Mg-Al MMOs can be obtained through the calcination of P123-templated Mg-Al-CO{sub 3} LDHs. The pore diameter is 2.2 nm. At the presence of ibuprofen, the Mg-Al MMOs can recover to Mg-Al-IBU LDHs, based on its 'remember effect'. Display Omitted

  13. 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

  14. Dynamical simulations of radiation damage in magnesium aluminate spinel, MgAl2O4

    NASA Astrophysics Data System (ADS)

    Smith, R.; Bacorisen, D.; Uberuaga, B. P.; Sickafus, K. E.; Ball, J. A.; Grimes, R. W.

    2005-02-01

    Collision cascades in MgAl2O4 are investigated using molecular dynamics simulations in order to determine the threshold displacement energies, Ed, and the damage imparted to the lattice at energies of up to 5 keV. The value of Ed is determined for MgAl2O4 on each of the Mg, Al and O sublattices for different orientations of the primary knock-on atom (PKA). The lowest Ed required to create permanent defects was for an O PKA along the \\langle 100\\rangle direction with a value of 27.5 eV, while the highest was 277.5 eV along \\langle 131\\rangle for an Mg PKA. Higher energy cascades show that a much wider variety of defects remain after the collisional phase than for similar cascades in MgO but the number of Frenkel pairs produced is smaller. The predominant defects that form are antisite defects on the cation sublattice only and O and Mg split interstitials orientated along the \\langle 110\\rangle direction. Some Mg-Al split interstitials centred on an Mg site were also observed. However, some more extended defect complexes can also arise which have no well defined structure.

  15. 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

  16. Reoxidation of Aluminum in Fe- Al- M (M = C, Mn, and Ti) melts with CaO-Al2 O3-Fe t O (3 mass pct) slags

    NASA Astrophysics Data System (ADS)

    Lee, Kwang Ro; Suito, Hideaki

    1996-06-01

    An Fe-0.01 to 0.5 mass pct Al alloy and an Fe-0.003 to 0.71 mass pct Al-1 mass pct M (M = C, Mn, and Ti) alloy were reoxidized with the CaO-Al2O3-FetO (3 mass pct) slags at 1873 K in an Al2O3 or CaO crucible for 5 and 60 minutes. The contents of acid-insoluble Al, total O, and alloying element M in metal as well as those of M and FetO in slag were measured as a function of total Al content. On the basis of the present and previous results for Fe- Al- Te alloys, the effect of alloying elements on the degree of supersaturation with respect to the Al2O3 precipitation was studied. As a result, the supersaturation phenomenon was observed in all experiments at 5 minutes, but in the experiments at 60 minutes, it was observed only in Fe- Al and Fe- Al- Ti alloys. No supersaturation was observed in the reoxidation of Si in Fe-0.13 to 0.98 mass pct Si alloys with the CaO-SiO2-FetO (3 mass pct) slags in a CaO crucible at 5 and 60 minutes.

  17. Bonding of WC with an iron aluminide (FeAl) intermetallic

    SciTech Connect

    Schneibel, J.H.; Subramanian, R.

    1996-08-01

    FeAl, which has high oxidation and sulfidation resistance, was shown to be thermodynamically compatible with WC. Calculations indicate that soly. of WC in liq. Fe-40at.%Al at 1450 C is about 2 at.%. Since liquid FeAl wets WC very well, the WC/FeAl system lends itself to liquid-phase sintering, resulting in close to theoretical densities. Almost fully dense cermets with 20.6 wt% FeAl binder were produced. With one-step infiltration, 98% dense cermets with only 7 wt% FeAl binder were fabricated. RT bend strengths and fracture toughness for WC-20.6 wt% FeAl reached 1680 MPa and 22 MPa{center_dot}m{sup 1/2}. Ductile binder fracture was observed on the fracture surfaces. Pores containing oxide inclusions were found, suggesting that improvements in processing are likely to further improve the mechanical properties. Insufficient process control may explain why WC/FeAlNi cermets did not show improved mechanical properties, although Ni strengthens FeAl. For WC bonded with FeAl, mechanical properties were measured at RT and 800 C. Bend strengths at 800 C in air increased with WC volume fraction, and fracture toughness were higher than at RT.

  18. Impact behavior of FeAl alloy FA-350

    SciTech Connect

    Alexander, D.J.

    1994-09-01

    The tensile properties and impact behavior of the iron aluminide FeAl-type alloy FA-350 [Fe-35.8Al-0.05Zr-0.24B (at. %)] have been studied over the temperature range of {minus}100 to 800C. Half-size Charpy specimens were either oil quenched from 700C or furnace cooled. The energy absorbed during the impact test showed a maximum value at 100 to 200C, with decreasing energy as the temperature was increased, for both heat treatments. The furnace-cooled material had greater energy absorption than the oil-quenched material. The tensile tests showed increasing ductility (as measured by total elongation) with increasing temperature. The furnace-cooled material had lower strength and higher ductility than the oil-quenched material. Fractographic examination of the oil-quenched impact specimens revealed that several different fracture modes operated, depending on the test temperature. Fracture occurred by intergranular and quasicleavage fracture at low temperatures, predominantly quasicleavage at intermediate temperatures, and intergranular fracture at 800C. For the furnace-cooled material fracture was predominantly quasicleavage at all temperatures. The higher ductility and energy absorption for the furnace-cooled material is believed to be the result of softening due to a decrease in the retained vacancy concentration.

  19. Weldability of Fe[sub 3]Al-type Aluminide

    SciTech Connect

    David, S.A.; Zacharia, T. )

    1993-05-01

    An investigation was carried out to determine the weldability of a series of Fe[sub 3]Al-type alloys. Autogenous welds were made on thin sheets of iron aluminide alloys using gas tungsten arc (GTA) and electron beam (EB) welding processes at different travel speeds and power levels. The results indicate that although these alloys can be successfully welded using the EB welding process, some compositions may hot crack during GTA welding. Boron and zirconium additions have been found to promote hot cracking in these alloys. Among the alloys investigated, Fe[sub 3]Al modified with chromium, niobium and carbon (FA-129) showed the most promise for good weldability. Hot-cracking severity of this alloy was further investigated using the Sigmajig test. The minimum threshold stress of 25 ksi measured is within the material range of other aluminides and some commercial stainless steels. Also, some of these alloys exhibited a tendency for cold cracking. This is related to severe hydrogen embrittlement associated with this class of alloys.

  20. Evidence for boron diffusion into sub-stoichiometric MgO (001) barriers in CoFeB/MgO-based magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Harnchana, V.; Hindmarch, A. T.; Sarahan, M. C.; Marrows, C. H.; Brown, A. P.; Brydson, R. M. D.

    2013-04-01

    Evidence of boron diffusion into the MgO barrier of a CoFeB/MgO based magnetic tunnel junction has been identified using analytical scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy. Structures were deposited by DC/RF-magnetron sputtering, where defective, sub-stoichiometric MgO barriers degrading device performance have been previously mitigated against by deposition of thin Mg layers prior to MgO deposition. We show that despite the protection offered by the Mg layer, disorder in the MgO barrier is still evident by STEM analysis and is a consequence of the oxidation of the Co40Fe40B20 surface during MgO deposition. Evidence of boron diffusion from CoFeB into the MgO barrier in the as-deposited and annealed structure is also presented, which in the as-deposited case we suggest results from the defective structures at the barrier interfaces. Annealing at 375 °C results in the presence of B in the trigonal coordination of [BO3]3- in the MgO barrier and partial crystallization of the top electrode (we presume there is also some boron diffusion into the Ta capping layer). The bottom electrode, however, fails to crystallize and much of the boron is retained in this thicker electrode. A higher annealing temperature or lower initial boron content is required to crystallize the bottom electrode.

  1. Pressure dependence of the magneto-transport properties in Fe/MgO granular systems

    NASA Astrophysics Data System (ADS)

    García-García, A.; Algarabel, P. A.; Pardo, J. A.; Arnold, Z.; Kamarad, J.

    2013-05-01

    The effect of hydrostatic pressure at room temperature on the resistance and magnetoresistance (MR) of a discontinuous metal-insulator multilayer (DMIM) of nominal composition [Fe( t Fe = 0.7 nm)/MgO( t MgO = 3 nm)]15 has been studied. The resistivity of the DMIM, ρ, decreases linearly with pressure indicating an increase in conduction via tunneling effect. The value of coefficient (1 /ρ 0) dρ/dP = -3.9 × 10-2 kbar-1 is higher than reported values in other granular films implying that the electronic state of the DMIM is close to the iron percolation threshold. At the maximum applied magnetic field (3 kOe) the MR ratio increases from 0.6% at ambient pressure to 1.1% at 7 kbar. This result can be explained by a reduction of the tunnel barrier width induced by the hydrostatic pressure.

  2. Interfacial perpendicular magnetic anisotropy in CoFeB/MgO structure with various underlayers

    NASA Astrophysics Data System (ADS)

    Oh, Young-Wan; Lee, Kyeong-Dong; Jeong, Jong-Ryul; Park, Byong-Guk

    2014-05-01

    Interfacial perpendicular magnetic anisotropy (PMA) in CoFeB/MgO structures was investigated and found to be critically relied on underlayer material and annealing temperature. With Ta or Hf underlayer, clear PMA is observed in as-deposited samples while no PMA was shown in those with Pt or Pd. This may be attributed to smaller saturation magnetization of the films with Ta or Hf underlayer, which makes the PMA of CoFeB/MgO interface dominates over demagnetization field. On the contrary, samples with Pt or Pd demonstrate PMA only after annealing, which might be due to the CoPt (or CoPd) alloy formation that enhances PMA.

  3. Nonvolatile photorefractive properties in triply doped stoichiometric Mg:Fe:Mn:LiTaO3 crystals

    NASA Astrophysics Data System (ADS)

    Sun, Ting; Zhang, Xiao-Dong; Sun, Liang; Wang, Rui

    2014-01-01

    We have grown triply doped Mg:Fe:Mn:LiTaO3 crystals with near stoichiometry using the top seeded solution growth technique. The defect structure was investigated by infrared absorption spectra and Curie temperature. Using a blue laser as the source, excellent photorefractive properties were obtained. Nonvolatile holographic storage properties were investigated using the dual wavelength technique. We got a very high fixed diffraction efficiency and nonvolatile holographic storage sensitivity. The blue light has more than enough energy to excite holes of deep (Mn) and shallow (Fe) trap centers with the same phase, which enhance dramatically the blue photorefractive properties and the nonvolatile holographic storage. Mg2+ ion is no longer damage resistant at blue laser, but enhances photorefractive characteristics.

  4. 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}.

  5. 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.

  6. 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

  7. 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

  8. 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.

  9. 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.

  10. Surface study of fine MgFe 2O 4 ferrite powder prepared by chemical methods

    NASA Astrophysics Data System (ADS)

    Aono, Hiromichi; Hirazawa, Hideyuki; Naohara, Takashi; Maehara, Tsunehiro

    2008-02-01

    To study surface behaviors, MgFe 2O 4 ferrite materials having different grain sizes were synthesized by two different chemical methods, i.e., a polymerization method and a reverse coprecipitation method. The single phase of the cubic MgFe 2O 4 was confirmed by the X-ray diffraction method for both the precursors decomposed at 600-1000 °C except for a very small peak of Fe 2O 3 was detected for the samples calcined at 600 and 700 °C by the polymerization method. The crystal size and particle size increased with an increase in the sintering temperature using both methods. The conductance of the MgFe 2O 4 decreased when the atmosphere was changed from ambient air to air containing 10.0 ppm NO 2. The conductance change, C = G(air)/ G(10 ppm NO 2), was reduced with an increase in the operating temperature. For the polymerization method, the maximum C-value was ca. 40 at 300 °C for the samples sintered at 900 °C. However, the samples sintered at 1000 °C showed a low conductance change in the 10 ppm NO 2 gas, because the ratio of the O 2 gas adsorption sites on the particle surface is smaller than those of the samples having a high C-value. The low Mg content on the surface affects the low ratio of the gas adsorption sites. For the reverse coprecipitation method, the particle size was smaller than that of the polymerization method. Although a stable conductance was obtained for the sample sintered at 900 and 1000 °C, its conductance change was less than that of the polymerization method.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. Ionic-liquid gating of perpendicularly magnetised CoFeB/MgO thin films

    NASA Astrophysics Data System (ADS)

    Liu, Y. T.; Agnus, G.; Ono, S.; Ranno, L.; Bernand-Mantel, A.; Soucaille, R.; Adam, J.-P.; Langer, J.; Ocker, B.; Ravelosona, D.; Herrera Diez, L.

    2016-07-01

    We present the modulation of anisotropy field, coercivity, and domain wall (DW) velocity in CoFeB/MgO thin films with perpendicular anisotropy by applying voltages across an ionic liquid gate. Domain wall velocities in the creep regime can be modulated by a factor of 4.2, and the anisotropy field of the device can be modulated by 40 mT when going from +0.8 V to -0.8 V. The applied E-fields are seen to significantly influence DWs' pinning, depinning, and nucleation processes. In addition, we report on the evolution of the magnetic properties of the liquid/solid device as a function of time going from the pristine CoFeB/MgO film through device fabrication and operation up to one month. These results show that the solid/liquid device structure based on CoFeB/MgO thin films can be an efficient way to control magnetic properties with voltages below 1 V.

  17. Mechanical Responses of Superlight β-Based Mg-Li-Al-Zn Wrought Alloys under Resonance

    NASA Astrophysics Data System (ADS)

    Song, Jenn-Ming; Lin, Yi-Hua; Su, Chien-Wei; Wang, Jian-Yih

    2009-05-01

    To extend the application of lightweight Mg alloys in the automotive industry, this study suggests a β-based Mg-Li alloy (LAZ1110) with superior vibration fracture resistance by means of material design. In the cold-rolled state, a strengthened β matrix by the additions of Al and Zn, as well as intergranular platelike α precipitates, which are able to stunt the crack growth, contributes to a comparable vibration life with commercial Mg-Al-Zn alloys under a similar strain condition.

  18. Superconducting MgB2 thin films grown by pulsed laser deposition on Al2O3(0001) and MgO(100) substrates

    NASA Astrophysics Data System (ADS)

    Wang, S. F.; Dai, S. Y.; Zhou, Y. L.; Chen, Z. H.; Cui, D. F.; Xu, J. D.; He, M.; Lu, H. B.; Yang, G. Z.; Fu, G. S.; Han, L.

    2001-11-01

    Superconducting MgB2 thin films were fabricated on Al2O3(0001) and MgO(100) substrates by a two-step method. Boron thin films were deposited by pulsed laser deposition followed by an ex-situ annealing process. Resistance measurements of the deposited MgB2 films show a Tc of 38.6 K for MgB2/Al2O3 and 38.1 K for MgB2/MgO. Atomic force microscopy, scanning electron microscopy and x-ray diffraction were used to study the properties of the films. The results indicate that the MgB2/Al2O3 films consist of well-crystallized grains with a highly c-axis-oriented structure while the MgB2/MgO films have a dense uniform appearance with an unfixed orientation.

  19. 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.

  20. Adhesion of Escherichia coli to nano-Fe/Al oxides and its effect on the surface chemical properties of Fe/Al oxides.

    PubMed

    Liu, Zhao-Dong; Li, Jiu-Yu; Jiang, Jun; Hong, Zhi-Neng; Xu, Ren-Kou

    2013-10-01

    We investigated the adhesion of Escherichia coli to α-Fe2O3 and γ-Al2O3 and the effects of adhesion on the surface properties