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Sample records for mg-al based alloys

  1. Study on Mg/Al Weld Seam Based on Zn–Mg–Al Ternary Alloy

    PubMed Central

    Liu, Liming; Liu, Fei; Zhu, Meili

    2014-01-01

    Based on the idea of alloying welding seams, a series of Zn–xAl filler metals was calculated and designed for joining Mg/Al dissimilar metals by gas tungsten arc (GTA) welding. An infrared thermography system was used to measure the temperature of the welding pool during the welding process to investigate the solidification process. It was found that the mechanical properties of the welded joints were improved with the increasing of the Al content in the Zn–xAl filler metals, and when Zn–30Al was used as the filler metal, the ultimate tensile strength could reach a maximum of 120 MPa. The reason for the average tensile strength of the joint increasing was that the weak zone of the joint using Zn–30Al filler metal was generated primarily by α-Al instead of MgZn2. When Zn–40Al was used as the filler metal, a new transition zone, about 20 μm-wide, appeared in the edge of the fusion zone near the Mg base metal. Due to the transition zones consisting of MgZn2- and Al-based solid solution, the mechanical property of the joints was deteriorated. PMID:28788508

  2. Development of Creep Resistant Mg-Al-Sr Alloys

    NASA Astrophysics Data System (ADS)

    Pekguleryuz, Mihriban O.; Baril, Eric

    There have been attempts since in the 70's to develop creep resistant magnesium diecasting alloys for automotive applications such as automatic-transmission case and engine components. The earliest die casting alloys developed as a result of these activities were the Mg-Al- RE and Mg-Al-Si systems (AE and AS alloys). The shortcomings of these two alloy systems related to high cost or borderline properties have led to renewed activity in the 90's in the development of magnesium alloys with improved elevaied-temperature properties. This paper presents the development of a new family of creep-resistant Mg alloys based on the Mg-Al-Sr system. Creep resistance, the tensile yield strength and the bolt-load-retention of these alloys at 150°C and 175°C show improvement over Mg-Al-RE and Mg-Al-Si system. The microstructure of the alloys is characterized by Al-Sr-(Mg) containing intermetallic second phases. The absence of the Mg17Al12 phase in the microstructure, either creep-induced or as-cast, is one of the factors that contribute to improved creep-resistance of these alloys over the Mg-Al based diecasting alloys. Furthermore, the alloys exhibit better salt-spray corrosion resistance (0.09-0.15mg/cm2/day) than other commercial magnesium diecasting alloys such as AM60B, AS41, AE42 and the aluminum diecasting alloy A380.

  3. 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.

  4. Rapidly solidified Mg-Al-Zn-rare earth alloys

    SciTech Connect

    Chang, C.F.; Das, S.K.; Raybould, D.

    1987-01-01

    Among the light metal alloys, magnesium is the lightest structural material except for beryllium, and yet magnesium alloys have not seen extensive use because of their poor strength and corrosion resistance. Rapid solidification technology offers a possible solution to these problems. A number of Mg-Al-Zn alloys containing rare earth (RE) elements (e.g. Ce, Pr, Y, and Nd) have been investigated using rapid solidification processing for possible structural applications. The processing consists of planar flow or jet casting into ribbons, pulverization of ribbon to powder, and consolidation of powder into bulk shapes. The mechanical properties of some of these alloys show attractive combinations of strength, ductility and corrosion resistance. The microstructures of these alloys are correlated with their mechanical properties. The rapidly solidified Mg-Al-Zn-RE alloys show great potential for applications in automotive and aerospace industries. 7 references.

  5. Hot Cracking Susceptibility of Binary Mg-Al Alloys

    NASA Astrophysics Data System (ADS)

    Cao, Guoping; Kou, Sindo; Chang, Y. Austin

    The susceptibility of binary Mg-Al alloys in permanent mold casting was tested, including Mg-0.25Al, Mg-0.6Al, Mg-1Al, Mg-2Al, Mg-4Al and Mg-8Al (all in wt %). A steel mold was used for constrained rod casting (CRC), in which rods of various lengths were cast with sudden enlargement at both ends of each rod to prevent it from free contraction during solidification and thus induce hot cracking. The cooling rate near the location of cracking was measured. The hot cracking susceptibility was evaluated based on the widths and locations of the cracks observed. The curve of crack susceptibility vs. Al content was determined and compared with previous curves based on ring casting in steel molds and constrained rod casting in sand molds. The Scheil model of solidification was used to calculate the curves of temperature vs. fraction solid (T-fS) of the alloys. The crack susceptibility curve based on a simplified hot cracking criterion and the T-fS and cooling curves was compared with that based on CRC.

  6. Hydrogen absorption and desorption in rapidly solidified Mg- Al alloys

    NASA Astrophysics Data System (ADS)

    Urgnani, J.; Di Chio, M.; Palumbo, M.; Feuerbacher, M.; Fernandez, J. F.; Leardini, F.; Baricco, M.

    2009-01-01

    The addition of Al to Mg has been indicated as a suitable way to destabilise the hydride phase, in order to bring the absorption and desorption reactions close to reasonable temperatures and pressure values for hydrogen storage. Rapid solidification is known to refine the microstructure of Mg-Al alloys and it might improve the H2 absorption/desorption kinetics. In this paper, the interaction of H2 with rapidly solidified Mg-Al alloys have been studied for three different composition: Mg38.5Al61.5, Mg69Al31 and Mg72Al28. For Mg72Al28, no significant changes in the microstructure have been obtained by rapid solidification. In Mg69Al31, a significant grain refinement has been observed, whereas, for Mg38.5Al61.5, the formation of a metastable hexagonal phase has been found. In all cases, a disproportionation reaction has been observed after H2 absorption, leading to MgH2. After heating up to 430 °C the hydrogenated samples, a main desorption reaction from MgH2 has been observed, which brings again to the starting phases. Experimental results have been discussed on the basis of a thermodynamic assessment of the Mg-Al-H system.

  7. Characterisation of magnesium oxide and its interface with α-Mg in Mg-Al-based alloys

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Fan, Z.; Zhou, X.; Thompson, G. E.

    2011-08-01

    Magnesium oxide (MgO) films and particles have been collected by pressurised filtration of a Mg-8.6wt%Al-0.67wt%Zn (AZ91D) alloy melt. The morphology of the oxides and their interfaces with the α-Mg phase were investigated by high-resolution transmission electron microscopy. It was found that the oxide films consisted of large numbers of sub-micrometre-sized MgO particles, and that melt shearing can effectively break up the oxide films and disperse the oxide particles. For the first time, orientation relationships (ORs) of OR I: [1 overline 1 1]MgO∼2° from (0 0 0 1)α-Mg and (0 1 1)MgO //[2 overline 1 overline 1 0)α-Mg; and OR II: (overline 1 overline 1 1)MgO//(1 overline 1 0 1)α-Mg and [0 1 1]MgO//[overline 1 2 overline 1 1]α-Mg, were observed between the MgO particles and the α-Mg matrix. The calculated Bramfitt planar disregistries were 5.5% and 2.5% for the two ORs, respectively, indicating good lattice matching between MgO and α-Mg at the interface. With the evidence of grain refinement effect observed in the sheared AZ91D magnesium alloy, the possibility of MgO particles to act as potent nucleants for heterogeneous nucleation of α-Mg grains is discussed in terms of the crystallographic criterion.

  8. 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.

  9. High Strength, Nano-Structured Mg-Al-Zn Alloy

    DTIC Science & Technology

    2011-01-01

    REPORT High strength, nano-structured Mg– Al – Zn alloy 14. ABSTRACT 16. SECURITY CLASSIFICATION OF: The mechanical behavior and microstructure of...Prescribed by ANSI Std. Z39.18 - High strength, nano-structured Mg– Al – Zn alloy Report Title ABSTRACT The mechanical behavior and microstructure of...strength, nano-structured Mg– Al – Zn alloy Block 13: Supplementary Note © 2011 . Published in Materials Science and Engineering, Vol. 528, (54), Ed. 0 (2011

  10. Formation and Corrosion Resistance of Mg-Al Hydrotalcite Film on Mg-Gd-Zn Alloy

    NASA Astrophysics Data System (ADS)

    Ba, Z. X.; Dong, Q. S.; Kong, S. X.; Zhang, X. B.; Xue, Y. J.; Chen, Y. J.

    2017-06-01

    An environment-friendly technique for depositing a Mg-Al hydrotalcite (HT) (Mg6Al2(OH)16-CO3ṡ4H2O) conversion film was developed to protect the Mg-Gd-Zn alloy from corrosion. The morphology and chemical compositions of the film were analyzed by scanning electronic microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Raman spectroscopy (RS), respectively. The electrochemical test and hydrogen evolution test were employed to evaluate the biocorrosion behavior of Mg-Gd-Zn alloy coated with the Mg-Al HT film in the simulated body fluid (SBF). It was found that the formation of Mg-Al HT film was a transition from amorphous precursor to a crystalline HT structure. The HT film can effectively improve the corrosion resistance of magnesium alloy. It indicates that the process provides a promising approach to modify Mg-Gd-Zn alloy.

  11. Dual-scale phase-field simulation of Mg-Al alloy solidification

    NASA Astrophysics Data System (ADS)

    Monas, A.; Shchyglo, O.; Höche, D.; Tegeler, M.; Steinbach, I.

    2015-06-01

    Phase-field simulations of the nucleation and growth of primary α-Mg phase as well as secondary, β-phase of a Mg-Al alloy are presented. The nucleation model for α- and β-Mg phases is based on the “free growth model” by Greer et al.. After the α-Mg phase solidification we study a divorced eutectic growth of α- and β-Mg phases in a zoomed in melt channel between α-phase dendrites. The simulated cooling curves and final microstructures of α-grains are compared with experiments. In order to further enhance the resolution of the interdendritic region a high-performance computing approach has been used allowing significant simulation speed gain when using supercomputing facilities.

  12. The Evolution of As-cast Microstructure of Ternary Mg-Al-Zn Alloys: An Experimental and Modeling Study

    NASA Astrophysics Data System (ADS)

    Paliwal, Manas; Kang, Dae Hoon; Essadiqi, Elhachmi; Jung, In-Ho

    2014-07-01

    A numerical formulation of solidification model which can predict the microsegregation and microstructural features for multicomponent alloys is presented. The model incorporates the kinetic features during solidification such as solute back diffusion, dendrite tip undercooling, and secondary arm coarsening. The model is dynamically linked to thermodynamic library for accurate input of thermodynamic data. The modeling results are tested against the directional solidification experiments for Mg-Al-Zn alloys. The experiments were conducted in the cooling rate range of 0.13 to 2.33 K/s and microstructural features such as secondary arm spacing, primary dendrite arm spacing, second phase fraction, and microsegregation were compared with the modeling results. Based on the model and the experimental data, a solidification map was built in order to provide guidelines for as-cast microstructural features of Mg-Al-Zn alloys in a wide range of solidification conditions.

  13. Variations of Microsegregation and Second Phase Fraction of Binary Mg-Al Alloys with Solidification Parameters

    NASA Astrophysics Data System (ADS)

    Paliwal, Manas; Kang, Dae Hoon; Essadiqi, Elhachmi; Jung, In-Ho

    2014-07-01

    A systematic experimental investigation on microsegregation and second phase fraction of Mg-Al binary alloys (3, 6, and 9 wt pct Al) has been carried out over a wide range of cooling rates (0.05 to 700 K/s) by employing various casting techniques. In order to explain the experimental results, a solidification model that takes into account dendrite tip undercooling, eutectic undercooling, solute back diffusion, and secondary dendrite arm coarsening was also developed in dynamic linkage with an accurate thermodynamic database. From the experimental data and solidification model, it was found that the second phase fraction in the solidified microstructure is not determined only by cooling rate but varied independently with thermal gradient and solidification velocity. Lastly, the second phase fraction maps for Mg-Al alloys were calculated from the solidification model.

  14. In situ transmission electron microscopy observations of precipitation and a new orientation relationship between γ-Mg17Al12 and magnesium-based matrix in an Mg-Al-Zn-Sn alloy

    NASA Astrophysics Data System (ADS)

    Liu, Yu; Zhao, Dongshan; Nie, Xin; Tao, Hongyu; Wang, Jianbo; Gui, Jianian

    2012-12-01

    An in situ observation of the precipitation of γ-Mg17Al12 phase in a die-cast Mg-Al-Zn-Sn alloy was performed using a transmission electron microscope equipped with a heating stage maintained at 403 K for 100 min. The addition of a small amount of Sn to the AZ91 system accelerates the development of the γ-Mg17Al12 phase formed during continuous precipitation. A new orientation relationship between the γ-Mg17Al12 precipitate and α-Mg matrix was identified as ? .

  15. High-resolution electron microscopy observations of continuous precipitates with Pitsch-Schrader orientation relationship in an Mg-Al based alloy and interpretation with the O-lattice theory.

    PubMed

    Zhou, J P; Zhao, D S; Zheng, O; Wang, J B; Xiong, D X; Sun, Z F; Gui, J N; Wang, R H

    2009-12-01

    High-resolution electron microscopy was applied to analyze the continuous precipitated particles of the gamma-Mg(17)Al(12) phase with Pitsch-Schrader OR in the heat-treated AZ91 alloy at 473 K for 8 h. The existence of a continuous precipitated particle with the Pitsch-Schrader OR including the selection of the habit plane and the growth direction in Mg-Al system is rationalized by the constrained coincidence site lattice/constrained complete pattern shift lattice (CCSL/CDSCL) model and the O-lattice theory.

  16. Microstructural Aspects of Grain Boundary Bulge in a Dynamically Recrystallized Mg-Al-Zn Alloy

    NASA Astrophysics Data System (ADS)

    Sun, D. K.; Chang, C. P.; Kao, P. W.

    2010-07-01

    Microstructural features of grain boundary bulging have been studied in a dynamically recrystallized (DRXed) Mg-Al-Zn alloy. Unidirectional compression was used to deform the specimens to different strains at 473 K (200 °C). Microstructural characterization of the deformed specimens was performed by using both scanning electron microscopy and transmission electron microscopy (TEM). From the present results, it is suggested that in AZ31 Mg alloy, the DRXed grain is developed from grain boundary bulging. After a grain boundary segment starts to bulge, a bridging dislocation wall forms and anchors the bulged grain boundary. During further deformation, the misorientation of this bridging wall gradually increases, then transforms into a grain boundary, and a DRXed grain forms. Electron backscattered diffraction was used to study the orientation relationship between bulges/DRXed grains and the parent grains, and no special orientation relationship was found between them.

  17. Resistivity Changes Due to Precipitation Effects in Fibre Reinforced Mg-Al-Zn-Mn Alloy

    NASA Astrophysics Data System (ADS)

    Kiehn, J.; Kainer, K. U.; Vostrý, P.; Stulíková, I.

    1997-05-01

    The change of electrical properties of alumina short fibre reinforced Mg-Al-Zn-Mn alloy AZ91D during isochronal annealing up to 300 °C is discussed. The Saffil® fibres were incorporated into the magnesium alloy by direct squeeze casting. The fibre distribution is random planar parallel to the flat faces of the dc four-point resistivity specimens machined from the solution treated castings. A sharp drop of resistivity between 140 and 260 °C is explained by the formation of incoherent -phase particles. Some practical recommendations concerning the use of alumina short fibre reinforced AZ91 alloy are made on the basis of the results obtained. Es werden die Änderungen der elektrischen Eigenschaften der aluminiumoxid-kurzfaserverstärkten Mg-Al-Zn-Mn Legierung AZ91D während isochroner Wärmebehandlungen bis 300 °C diskutiert. Das direkte Preßgießverfahren diente zur Herstellung der Saffil®-Faser Magnesium Verbundwerkstoffe. Die Proben zur Widerstandsmessung nach der Vier-Punkt Methode wurden durch spanende Bearbeitung aus den lösungsgeglühten Preßgußstücken herausgearbeitet, so daß sie regellose Faserverteilung in den Ebenen parallel zu den flachen Probenseiten aufwiesen. Ein starker Abfall des elektrischen Widerstands im Temperaturbereich zwischen 140 und 260 °C wird durch die Bildung inkohärenter β-Phase erklärt. Auf Grundlage der Ergebnisse werden einige Empfehlungen zur Anwendung der kurzfaserverstärkten Legierung AZ91 gegeben.

  18. Numerical simulation of non-dendritic structure formation in Mg-Al alloy solidified with ultrasonic field.

    PubMed

    Feng, Xiaohui; Zhao, Fuze; Jia, Hongmin; Li, Yingju; Yang, Yuansheng

    2018-01-01

    The formation of non-dendritic structure of Mg alloy solidified with ultrasonic treatment was investigated by numerical simulation and experiment. The models of nucleation and crystal growth involved the effects of ultrasonic cavitation and acoustic streaming were built. Based on the models, the grain refinement and the microstructure change from dendrite to non-dendritic structure of a Mg-Al alloy were numerically simulated by cellular automata method. The simulation and experimental results indicated that the ultrasonic cavitation strongly contributes to the grain refinement by improving nucleation, while the acoustic streaming is mainly responsible for the formation of non-dendritic structure. Copyright © 2017 Elsevier B.V. All rights reserved.

  19. Orientation relationship between the T structure and the icosahedral quasicrystal in the Zn-Mg-Al alloy system

    SciTech Connect

    Nakayama, Kei Watanabe, Junya; Koyama, Yasumasa

    2016-08-26

    To understand the crystallographic relation between the Bergman-type icosahedral quasicrystal and its approximant-T structure, we have investigated the crystallographic features of prepared Zn-Mg-Al alloy samples, mainly by transmission electron microscopy. It was found that there existed three kinds of regions: that is, C14-Laves, approximant-T, and icosahedral-quasicrystal regions, in Zn-Mg-Al alloy samples with the composition of Zn-36at.%Mg-9at.%Al. Among these regions, in particular, we tried to determine an orientation relationship between neighboring icosahedral-quasicrystal and approximant-T regions. Based on the determined relationship, for instance, four threefold rotatory-inversion axes in the T structure were found to be parallel to four of ten threefold rotatory-inversion axes in the icosahedral quasicrystal. It was thus understood that the atomic arrangements of the Bergman-type icosahedral quasicrystal and its approximant-T structure are likely to resemble each other.

  20. Orientation relationship between the T structure and the icosahedral quasicrystal in the Zn-Mg-Al alloy system

    NASA Astrophysics Data System (ADS)

    Nakayama, Kei; Watanabe, Junya; Koyama, Yasumasa

    2016-08-01

    To understand the crystallographic relation between the Bergman-type icosahedral quasicrystal and its approximant-T structure, we have investigated the crystallographic features of prepared Zn-Mg-Al alloy samples, mainly by transmission electron microscopy. It was found that there existed three kinds of regions: that is, C14-Laves, approximant-T, and icosahedral-quasicrystal regions, in Zn-Mg-Al alloy samples with the composition of Zn-36at.%Mg-9at.%Al. Among these regions, in particular, we tried to determine an orientation relationship between neighboring icosahedral-quasicrystal and approximant-T regions. Based on the determined relationship, for instance, four threefold rotatory-inversion axes in the T structure were found to be parallel to four of ten threefold rotatory-inversion axes in the icosahedral quasicrystal. It was thus understood that the atomic arrangements of the Bergman-type icosahedral quasicrystal and its approximant-T structure are likely to resemble each other.

  1. Surface and cut-edge corrosion behavior of Zn-Mg-Al alloy-coated steel sheets as a function of the alloy coating microstructure

    NASA Astrophysics Data System (ADS)

    Oh, Min-Suk; Kim, Sang-Heon; Kim, Jong-Sang; Lee, Jae-Won; Shon, Je-Ha; Jin, Young-Sool

    2016-01-01

    The effects of Mg and Al content on the microstructure and corrosion resistance of hot-dip Zn-Mg-Al alloycoated steel sheets were investigated. Pure Zn and Zn-based alloy coatings containing Mg (0-5 wt%) and Al (0.2-55 wt%) were produced by a hot-dip galvanizing method. Mg and Al addition induced formation of intermetallic microstructures, like primary Zn, Zn/MgZn2 binary eutectic, dendric Zn/Al eutectoid, and Zn/Al/MgZn2/ternary eutectic structures in the coating layer. MgZn2-related structures (Zn/MgZn2, Zn/Al/MgZn2, MgZn2) played an important role in increasing the corrosion resistance of Zn-Mg-Al alloy-coated steel sheets. Zn-3%Mg-2.5%Al coating layer containing a large volume of lamellar-shaped Zn/MgZn2 binary eutectic structures showed the best cut-edge corrosion resistance. The analysis indicated that Mg dissolved from MgZn2 in the early stage of corrosion and migrated to the cathodic region of steel-exposed cut-edge area to form dense and ordered protective corrosion products, leading to prolonged cathodic protection of Zn-Mg-Al alloy-coated steel sheets.

  2. Synthesis of Al₂Ca Dispersoids by Powder Metallurgy Using a Mg-Al Alloy and CaO Particles.

    PubMed

    Fujita, Junji; Umeda, Junko; Kondoh, Katsuyoshi

    2017-06-28

    The elemental mixture of Mg-6 wt %Al-1 wt %Zn-0.3 wt %Mn (AZ61B) alloy powder and CaO particles was consolidated by an equal-channel angular bulk mechanical alloying (ECABMA) process to form a composite precursor. Subsequently, the precursor was subjected to a heat treatment to synthesize fine Al₂Ca particles via a solid-state reaction between the Mg-Al matrix and CaO additives. Scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS) and electron probe micro-analysis on the precursor indicated that 4.7-at % Al atoms formed a supersaturated solid solution in the α-Mg matrix. Transmission electron microscopy-EDS and X-ray diffraction analyses on the AZ61B composite precursor with 10-vol % CaO particles obtained by heat treatment confirmed that CaO additives were thermally decomposed in the Mg-Al alloy, and the solid-soluted Ca atoms diffused along the α-Mg grain boundaries. Al atoms also diffused to the grain boundaries because of attraction to the Ca atoms resulting from a strong reactivity between Al and Ca. As a result, needle-like (Mg,Al)₂Ca intermetallics were formed as intermediate precipitates in the initial reaction stage during the heat treatment. Finally, the precipitates were transformed into spherical Al₂Ca particles by the substitution of Al atoms for Mg atoms in (Mg,Al)₂Ca after a long heat treatment.

  3. Rare Earth Element Yttrium Modified Mg-Al-Zn Alloy: Microstructure, Degradation Properties and Hardness

    PubMed Central

    Liu, Long; Yuan, Fulai; Zhao, Mingchun; Gao, Chengde; Feng, Pei; Yang, Youwen; Yang, Sheng; Shuai, Cijun

    2017-01-01

    The overly-fast degradation rates of magnesium-based alloys in the biological environment have limited their applications as biodegradable bone implants. In this study, rare earth element yttrium (Y) was introduced into AZ61 magnesium alloy (Mg-6Al-1Zn wt %) to control the degradation rate by laser rapid melting. The results showed that the degradation rate of AZ61 magnesium alloy was slowed down by adding Y. This was attributed to the reduction of Mg17Al12 phase and the formation of Al2Y phase that has a more active potential, which decreased galvanic corrosion resulting from its coupling with the anodic matrix phase. Meanwhile, the hardness increased as Y contents increased due to the uniform distribution of the Al2Y and Mg17Al12 phases. However, as the Y contents increased further, the formation of excessive Al2Y phase resulted in the increasing of degradation rate and the decreasing of hardness due to its agglomeration. PMID:28772837

  4. Rare Earth Element Yttrium Modified Mg-Al-Zn Alloy: Microstructure, Degradation Properties and Hardness.

    PubMed

    Liu, Long; Yuan, Fulai; Zhao, Mingchun; Gao, Chengde; Feng, Pei; Yang, Youwen; Yang, Sheng; Shuai, Cijun

    2017-04-28

    The overly-fast degradation rates of magnesium-based alloys in the biological environment have limited their applications as biodegradable bone implants. In this study, rare earth element yttrium (Y) was introduced into AZ61 magnesium alloy (Mg-6Al-1Zn wt %) to control the degradation rate by laser rapid melting. The results showed that the degradation rate of AZ61 magnesium alloy was slowed down by adding Y. This was attributed to the reduction of Mg17Al12 phase and the formation of Al₂Y phase that has a more active potential, which decreased galvanic corrosion resulting from its coupling with the anodic matrix phase. Meanwhile, the hardness increased as Y contents increased due to the uniform distribution of the Al₂Y and Mg17Al12 phases. However, as the Y contents increased further, the formation of excessive Al₂Y phase resulted in the increasing of degradation rate and the decreasing of hardness due to its agglomeration.

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

    PubMed

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

    2015-07-01

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

  6. Nucleation mechanism of discontinuous precipitation in Mg-Al alloys and relation with the morphology

    SciTech Connect

    Duly, D. . Dept. of Engineering); Brechet, Y. . Lab. de Thermodynamique et Physico-Chimie Metallurgiques)

    1994-09-01

    The nucleation rate of discontinuous precipitation in Mg-Al has been measured as a function of temperature, initial grain size and solute content. From these measurements, it appears that at high temperatures (T [ge] 220 C) all precipitation nodules nucleate via Fournelle and Clark's mechanism, whereas at lower temperatures (T [approximately] 140 C), at least one of the mechanisms identified by Tu and Turnbull or Purdy and Lange is also active. The proportion of double seam nodules determined by optical microscopy decreases from more than 1/2 to 0 when the temperature increases. In the low temperature domain, this behavior is in agreement with that predicted by Baumann, Williams and Michael.

  7. Microstructure and Properties of Aged vs. Crept Mg-Al-Zn-Sn Alloys with Additions of Nd and Ce

    NASA Astrophysics Data System (ADS)

    Vainberg, Uri; Avraham, Shaul; Katsman, Alexander; Bamberger, Menachem

    Mg-alloys are highly applicative at the automobile and aerospace industries due to their high specific mechanical properties. Mg-Al-RE alloy design was motivated by the formation of Al-RE intermetallic at the grain boundaries (GB) and Mg2Sn precipitates inside the α-Mg matrix. The presence of precipitates at the GB can inhibit GB sliding, while the precipitation inside the α-Mg matrix grains inhibits dislocation climb responsible for a bulk creep. Thermodynamic simulations were used for optimal composition and process parameters derivation. Mg-Al-Zn-Sn alloys with additions of Nd and Ce were examined in terms of creep resistance and microstructure development during aging and creep. The evolution of the microstructure was monitored by scanning electron microscopy and X-ray diffraction. Mechanical properties were examined by creep testing and Vickers microhardness measurements. A directional growth of the MgZn2 precipitates was found in the crept specimens in contrast to the aged counterparts.

  8. Characterization of the chemical conversion films that form on Mg-Al alloy in colloidal silica solution

    NASA Astrophysics Data System (ADS)

    Kim, Seong-Jong; Zhou, Ying; Ichino, Ryoichi; Okido, Masazumi; Tanikawa, Shoji

    2003-04-01

    Chemical conversion treatment of Mg-Al alloy (AZ91) using colloidal silica as an alternative to chromate conversion was investigated as a function of solution pH, temperature, solution conditions, and treatment time. The solution used for the colloidal silica coating consisted of colloidal silica, titanium sulfate, and cobalt ions to maintain good anti-corrosion and adhesion properties. Adding CoSO4 to the colloidal silica solution enhanced the adhesion force between the silica film and magnesium substrate. The optimum conditions for the chemical conversion treatment solution were pH 2, 90-sec treatment, and 25°C.

  9. Low-strain plasticity in a high pressure die cast Mg-Al alloy

    NASA Astrophysics Data System (ADS)

    Vanna Yang, K.; Cáceres, C. H.; Nagasekhar, A. V.; Easton, M. A.

    2012-03-01

    The Kocks-Mecking method was used to compare the strain-hardening behavior at low strains of high pressure die cast Mg-9 mass% Al alloy and gravity cast fine grained pure Mg specimens. The alloy specimens exhibited a rounded flow curve in contrast with the pure metal's for which macroscopic yielding occurred at a well-defined stress. Microhardness mapping of the cross-section of an alloy specimen showed a surface layer, or skin, with hardness values ˜20 HV above those of the centre or core region. On the assumption that the core strain hardens at the same rate as the pure Mg specimen, it was estimated that ˜20% of the alloy specimen's cross-section was still elastic when the core reached full plasticity. The micromechanics of the elasto-plastic transition in the alloy specimens are discussed.

  10. Precipitate Formation and Grain Refinement of MG-AL-SN Alloy during Hot Deformation

    NASA Astrophysics Data System (ADS)

    Kabir, Abu Syed Humaun; Su, Jing; Vo, Phuong; Jung, In-Ho; Yue, Stephen

    Magnesium alloys are very popular in the automobile industry due to its high strength to weight ratio. However, the use of commercial magnesium alloys as sheet is limited by room temperature ductility. One way to improve the ductility may be to form precipitates during hot rolling. These may delay dynamic recrystallization, possibly leading to grain refinement, which is known to improve ductility. Equilibrium diagrams obtained from thermodynamic modeling software FactSage were used to design Mg-3Al-2Sn alloy, which should form Mg2Sn precipitates during hot rolling temperatures around 300 °C. To investigate this prediction, the alloy was cast in a copper mould and precipitates formation characteristics were studied by using optical microscope (OM), scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDS).

  11. Potential of an Al-Ti-MgAl2O4 Master Alloy and Ultrasonic Cavitation in the Grain Refinement of a Cast Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    Sreekumar, V. M.; Babu, N. H.; Eskin, D. G.

    2017-02-01

    A new grain refining master alloy containing MgAl2O4 and Ti was synthesized by in situ reaction of TiO2 particles in an Al-Mg melt. MgAl2O4 particles formed were distributed in the melt by ultrasonic cavitation processing. The obtained master alloy showed considerable (50 pct) grain refining ability in a commercial A357-type Al-Si alloy. Ultrasonication contributed further to 25 pct in the grain refinement. In comparison with a commercial Al-5 pct Ti-1 pct B master alloy, the efficiency of the new master alloy is less at a lower addition rate. Nevertheless, both master alloys performed similarly at higher additions. The strength and ductility of the inoculated and ultrasonicated alloy showed at least a 10 pct and a 50 pct increase, respectively, as compared with non-grain-refined alloy and a similar mechanical performance in comparison with the alloy inoculated with Al-5 pct Ti-1 pct B master alloy.

  12. In Situ Synchrotron Radiation Diffraction during Melting and Solidification of Mg-Al Alloys Containing CaO

    NASA Astrophysics Data System (ADS)

    Wiese, B.; Mendis, C. L.; Tolnai, D.; Szakács, G.; Stark, A.; Schell, N.; Reichel, H. P.; Brückner, R.; Kainer, K. U.; Hort, N.

    Previous investigations show that CaO additions have an effect on the microstructure and mechanical properties of commercial Mg alloys. Addition of CaO to pure Mg and Mg alloys results in the dispersion of Ca in the molten and solid Mg with no evidence of CaO. This paper reports on the reactions between Mg, Al and CaO measured by means of in situ synchrotron radiation diffraction during melting and solidification. The experiment was conducted on Mg-3Al wt% with CaO concentrations between 3 wt% and 10 wt% to study the effect of different Al:CaO ratios. The initial sample contained Mg, Al and CaO in powder state, pressed to cylindrical samples. The melting, the solidification and associated phase transformations were measured in a Bähr 805A/D dilatometer inside a sealed stainless steel crucible at the High Energy Materials Science Beamline P07 at PETRA III, DESY.

  13. Effect of Ca addition on the damping capacity of Mg-Al-Zn casting alloys

    NASA Astrophysics Data System (ADS)

    Jun, Joong-Hwan; Moon, Jung-Hyun

    2015-07-01

    The influences of Ca addition on the microstructures and damping capacities of AZ91-(0˜2)%Ca casting alloys were investigated, on the basis of the results of X-ray diffractometry, optical microscopy, scanning electron microscopy and vibration tests in a single cantilever mode. The amount of intermetallic compounds decreased with increasing Ca content up to 0.5%, above which it increased; the average cell size showed the opposite tendency. All alloys exhibited similar damping levels in the strain-amplitude independent region. Considering the very low solubility of Ca in the matrix, and that most of the Ca elements are consumed by the formation of the Al2Ca phase and incorporation into the Mg17Al12 phase, this would be ascribed to the almost identical concentrations of Ca solutes distributed in the matrix. In the strain-amplitude dependent region, however, the AZ91-0.5%Ca alloy possessed the maximum damping capacity. From the viewpoint of microstructural evolution with Ca addition, the number density of compound particles is considered to be the principal factor affecting the damping behavior in the strain-amplitude dependent region.

  14. Strengthening Micromechanisms in Cold-Chamber High-Pressure Die-Cast Mg-Al Alloys

    NASA Astrophysics Data System (ADS)

    Yang, Kun V.; Cáceres, Carlos H.; Easton, Mark A.

    2014-08-01

    The contributions from grain boundary, solid solution, and dispersion strengthening to the yield strength of cast-to-shape specimens were calculated for seven binary alloys with compositions ranging from very dilute (0.5 mass pct Al) to concentrated (12 mass pct Al). Experimentally and theoretically determined parameters were used to explicitly account for the different microstructures at the skin and core regions of specimens' cross sections. Microhardness maps were used to identify the specimens' skin. The specimens' strength was calculated as the weighted addition of the respective strengths of skin and core. The calculated strengths reproduced well the experimental values for the dilute alloys but underestimated the strength of the most concentrated alloys by as much as ~35 MPa. It is argued that the presence of the percolating network of Mg17Al12 eutectic intermetallic, particularly in the skin region, in conjunction with highly efficient dispersion hardening due to the convoluted shape of the intermetallics, accounts for the shortfall in the calculated strength.

  15. Deformation Behavior and Dynamic Recrystallization of Micro-Alloyed Mg-Al-Ca Alloys During High Temperature Deformation

    NASA Astrophysics Data System (ADS)

    Su, Jing; Kabir, Abu Syed Humaun; Jung, In-Ho; Yue, Steve

    Two micro-alloyed magnesium alloys, Mg-0.3Al-0.2Ca (AX0302) and Mg-0.1Al-0.5Ca (AX0105), were designed based on the thermodynamics calculation in terms of precipitation temperature. Hot compression tests were conducted at temperatures of 300°C, 350°C and 400°C with strain rates of 0.1s-1, 0.01s-1 and 0.001s-1. Dynamic precipitation of Al2Ca could be found below 400°C in AX0302, while Mg2Ca dynamically formed in AX0105 during deformation at all three temperatures. At high temperature and low strain rate (400°C at 0.01s-1 and 0.001s-1 and 350°C at 0.001s-1), DRX mainly developed at the grain boundaries and formed necklace type microstructure in both alloys. However, at lower temperature and higher strain rate, DRX grains formed at both grain boundaries and twinning boundaries. The combination effect of twinning and dynamic precipitation on dynamic recrystallization was studied by comparing with two alloys.

  16. Texture Evaluation of a Bi-Modal Structure During Static Recrystallization of Hot-Deformed Mg-Al-Sn Alloy

    NASA Astrophysics Data System (ADS)

    Kabir, Abu Syed Humaun; Su, Jing; Yue, Stephen

    2016-12-01

    In this study, Mg-Al-Sn alloy was hot compressed at 523 K (250 °C) and annealed at 623 K (350 °C) for various times. The initial as-deformed microstructure was partially dynamic recrystallized with strain-induced precipitates on the recrystallized grain boundaries. After annealing at 623 K (350 °C), static recrystallization (SRX) of the bimodal microstructure took place where, at this temperature, no static precipitates formed. The goal of this work was to study the effect of dynamic precipitation on the texture evolution during the SRX process. Progressive texture evolution was studied during annealing by electron backscattered diffraction technique through a microstructure-tracking process. It was found that the grain-coarsening mechanism during the early stage of annealing is not totally controlled by the basal-oriented grains. Also, it was found that the dynamic precipitates may have significant influence in the early texture weakening during annealing of a bimodal structure.

  17. A method for intermediate strain rate compression testing and study of compressive failure mechanism of Mg-Al-Zn alloy

    NASA Astrophysics Data System (ADS)

    Gupta, Nikhil; Luong, Dung D.; Rohatgi, Pradeep K.

    2011-05-01

    Obtaining meaningful information from the test results is a challenge in the split-Hopkinson pressure bar (SHPB) test method if the specimen does not fail during the test. Although SHPB method is now widely used for high strain rate testing, this limitation has made it difficult to use it for characterization of materials in the intermediate strain rate range (typically 10-1000 s-1). In the present work, a method is developed to characterize materials in the intermediate strain rate range using SHPB setup. In this method, the specimen is repeatedly tested under compression at a given strain rate until failure is achieved. The stress-strain graphs obtained from each test cycle are used to plot the master stress-strain graph for that strain rate. This method is used to study the strain rate dependence of compressive response of a Mg-Al-Zn alloy in the intermediate strain rate range. A remarkable difference is observed in the failure mechanism of the alloy under quasi-static and intermediate strain rate compression. Matrix cracking is the main failure mechanism under quasi-static compression, whereas shattering of intermetallic precipitates, along with plastic deformation of the matrix, is discovered to become prominent as the strain rate is increased.

  18. Thermal analysis and microstructural characterization of Mg-Al-Zn system alloys

    NASA Astrophysics Data System (ADS)

    Król, M.; Tański, T.; Sitek, W.

    2015-11-01

    The influence of Zn amount and solidification rate on the characteristic temperature of the evaluation of magnesium dendrites during solidification at different cooling rates (0.6-2.5°C) were examined by thermal derivative analysis (TDA). The dendrite coherency point (DCP) is presented with a novel approach based on second derivative cooling curve. Solidification behavior was examined via one thermocouple thermal analysis method. Microstructural assessments were described by optical light microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. These studies showed that utilization of d2T/dt2 vs. the time curve methodology provides for analysis of the dendrite coherency point

  19. 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.

  20. 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.

  1. 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.

  2. Influence of anisotropic pressure on viscosity and electrorheology of diethylene glycol-based MgAl2O4 nanofluids.

    PubMed

    Zyła, Gaweł; Grzywa, Joanna; Witek, Adam; Cholewa, Marian

    2014-04-08

    The paper presents results of rheological experiments on viscosity under anisotropic pressure and in electric field of diethylene glycol-based MgAl2O4 nanofluids. Nanofluids have been prepared in a two-step method. The dynamic viscosity of nanofluids with various mass concentrations of nanoparticles was measured in the range of shear rates from 10 s -1 to 1,000 s -1 in constant temperature under the pressure of 7.5 MPa. In the second type of experiments, different values of the electric field up to 2,000 V/mm was used. Thixotropy structure of MgAl2O4-DG nanofluids has been studied in electrical field.

  3. Influence of anisotropic pressure on viscosity and electrorheology of diethylene glycol-based MgAl2O4 nanofluids

    PubMed Central

    2014-01-01

    The paper presents results of rheological experiments on viscosity under anisotropic pressure and in electric field of diethylene glycol-based MgAl2O4 nanofluids. Nanofluids have been prepared in a two-step method. The dynamic viscosity of nanofluids with various mass concentrations of nanoparticles was measured in the range of shear rates from 10 s −1 to 1,000 s −1 in constant temperature under the pressure of 7.5 MPa. In the second type of experiments, different values of the electric field up to 2,000 V/mm was used. Thixotropy structure of MgAl2O4-DG nanofluids has been studied in electrical field. PMID:24712490

  4. Evolution of microstructure and texture in Mg-Al-Zn alloys during electron-beam and gas tungsten arc welding

    NASA Astrophysics Data System (ADS)

    Wu, S. H.; Huang, J. C.; Wang, Y. N.

    2004-08-01

    The evolution of microstructure and texture in the AZ-series Mg alloys subjected to electron-beam welding and gas tungsten arc welding are examined. Electron-beam welding is demonstrated to be a promising means of welding delicate Mg plates, bars, or tubes with a thickness of up to 50 mm; gas tungsten arc welding is limited to lower-end thin Mg sheets. The grains in the fusion zone (FZ) are nearly equiaxed in shape and ˜8 µm or less in size, due to the rapid cooling rate. The as-welded FZ microhardness and tensile strength are higher than the base metals due to the smaller grain size. The weld efficiency, defined as the postweld microhardness or tensile strength at the mid-FZ region divided by that of the unwelded base metal, is around 110 to 125 pct for electron-beam welding and 97 to 110 pct for gas tungsten arc welding. There are three main texture components present in the electron-beam-welded (EBW) FZ, i.e., \\{ 10overline 1 1\\} < 10overline 1 overline 2 > (with TD// < 11overline 2 0 > ),\\{ 11overline 2 1\\} < 1bar 100 > (with ND∧ < 11overline 2 0 > ˜15 deg), and \\{ 10overline 1 0\\} < 11overline 2 2 > (with WD∧ < 11overline 2 0 > ˜30 deg), where TD, ND, and WD are the transverse, normal, and welding directions, respectively. The crystal growth tends to align toward the most closed-packed direction, < 11overline 2 0 > . The texture in gas tungsten arc welded (GTAW) specimens is more diverse and complicated than the EBW counterparts, due to the limited and shallow FZ and the lower cooling rate. The cooling rates calculated by the three-dimensional (3-D) and two-dimensional (2-D) heat-transfer models are considered to be the lower and upper bounds. The cooling rate increases with decreasing Al content, increasing weld speed, and increasing distance from the weld top surface. The influences of the FZ location, welding speed, and alloy content on the resulting texture components are rationalized and discussed.

  5. 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.

  6. Effect of Thermomechanical Processing on the Elevated Temperature Behavior of Lithium-Containing High-Mg, Al-Mg Alloys.

    DTIC Science & Technology

    1986-06-01

    predict as accurately as possible the true elongations from the charted values, a scale factor equal to the ratio of the measured elongation at...the volume fraction of precipitated B, Mg5AI8 , is the most influential factor affecting flow stress and strain-rate sensitivity. How Li additions...of 13 precipitated is the most influential factor affecting flow stress, - and strain-rate sensitivity coefficient, m. 7. The Al-Mg-Li alloys tested

  7. Starch Biocatalyst Based on α-Amylase-Mg/Al-Layered Double Hydroxide Nanohybrids.

    PubMed

    Bruna, Felipe; Pereira, Marita G; Polizeli, Maria de Lourdes T M; Valim, João B

    2015-08-26

    The design of new biocatalysts through the immobilization of enzymes, improving their stability and reuse, plays a major role in the development of sustainable methodologies toward the so-called green chemistry. In this work, α-amylase (AAM) biocatalyst based on Mg3Al-layered double-hydroxide (LDH) matrix was successfully developed with the adsorption method. The adsorption process was studied and optimized as a function of time and enzyme concentration. The biocatalyst was characterized, and the mechanism of interaction between AAM and LDH, as well as the immobilization effects on the catalytic activity, was elucidated. The adsorption process was fast and irreversible, thus yielding a stable biohybrid material. The immobilized AAM partially retained its enzymatic activity, and the biocatalyst rapidly hydrolyzed starch in an aqueous solution with enhanced efficiency at intermediate loading values of ca. 50 mg/g of AAM/LDH. Multiple attachments through electrostatic interactions affected the conformation of the immobilized enzyme on the LDH surface. The biocatalyst was successfully stored in its dry form, retaining 100% of its catalytic activity. The results reveal the potential usefulness of a LDH compound as a support of α-amylase for the hydrolysis of starch that may be applied in industrial and pharmaceutical processes as a simple, environmentally friendly, and low-cost biocatalyst.

  8. Surface enrichment of Pt in stable Pt-Ir nano-alloy particles on MgAl 2 O 4 spinel in oxidizing atmosphere

    DOE PAGES

    Li, Wei-Zhen; Nie, Lei; Cheng, Yingwen; ...

    2017-04-01

    With the capability of MgAl2O4 spinel {111} nano-facets in stabilizing small Rh, Ir and Pt particles, bimetallic Ir-Pt catalysts on the same support were investigated in this paper, aiming at further lowering the catalyst cost by substituting expensive Pt with cheaper Ir in the bulk. Small Pt-Ir nano-alloy particles (< 2 nm) were successfully stabilized on the spinel {111} nano-facets as expected. Interestingly, methanol oxidative dehydrogenation (ODH) rate on the surface Pt atoms increases with oxidizing aging but decreases upon reducing treatment, where Ir is almost inactive under the same reaction conditions. Up to three times enhancement in Pt exposuremore » was achieved when the sample was oxidized at 800 °C in air for 1 week and subsequently reduced by H2 for 2 h, demonstrating successful surface enrichment of Pt on Pt-Ir nano-alloy particles. Finally, a dynamic stabilization mechanism involving wetting/nucleation seems to be responsible for the evolution of surface compositions upon cyclic oxidizing and reducing thermal treatments.« less

  9. Surface enrichment of Pt in stable Pt-Ir nano-alloy particles on MgAl2O4 spinel in oxidizing atmosphere

    DOE PAGES

    Li, Wei -Zhen; Nie, Lei; Cheng, Yingwen; ...

    2017-01-13

    With the capability of MgAl2O4 spinel {111} nano-facets in stabilizing small Rh, Ir and Pt particles, bimetallic Ir-Pt catalysts on the same support were investigated in this paper, aiming at further lowering the catalyst cost by substituting expensive Pt with cheaper Ir in the bulk. Small Pt-Ir nano-alloy particles (< 2 nm) were successfully stabilized on the spinel {111} nano-facets as expected. Interestingly, methanol oxidative dehydrogenation (ODH) rate on the surface Pt atoms increases with oxidizing aging but decreases upon reducing treatment, where Ir is almost inactive under the same reaction conditions. Up to three times enhancement in Pt exposuremore » was achieved when the sample was oxidized at 800 °C in air for 1 week and subsequently reduced by H2 for 2 h, demonstrating successful surface enrichment of Pt on Pt-Ir nano-alloy particles. Finally, a dynamic stabilization mechanism involving wetting/nucleation seems to be responsible for the evolution of surface compositions upon cyclic oxidizing and reducing thermal treatments.« less

  10. 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.

  11. MgAl{sub 2}O{sub 4}(001) based magnetic tunnel junctions made by direct sputtering of a sintered spinel target

    SciTech Connect

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

    2016-03-28

    We developed a fabrication process of an epitaxial MgAl{sub 2}O{sub 4} barrier for magnetic tunnel junctions (MTJs) using a direct sputtering method from an MgAl{sub 2}O{sub 4} spinel sintered target. Annealing the sputter-deposited MgAl{sub 2}O{sub 4} 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/MgAl{sub 2}O{sub 4}/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.

  12. The Effect of Friction Stir Processing by Stepped Tools on the Microstructure, Mechanical Properties and Wear Behavior of a Mg-Al-Zn Alloy

    NASA Astrophysics Data System (ADS)

    Arab, Seyed Mohammad; Jahromi, Seyed Ahmad Jenabali; Zebarjad, Seyed Mojtaba

    2016-10-01

    Friction stir processing (FSP) which imposes severe plastic strains has been used as a solid-state process to refine the grain structure of a Mg-Al-Zn alloy and therefore to enhance the strength and wear resistance without significant reduction of ductility. The introduced stepped tools result in more uniform microstructure, and therefore higher mechanical properties, as well as enhanced wear resistance. More passes of FSP could lead to more uniform microstructure and finer grains. The grain size was reduced from above 40 µm to below 4 µm. The pin root hole defect is also reduced during FSP by the stepped tools especially by cylindrical one. Microhardness was increased more than two times compared with the as-received sample. The tensile strength and elongation are almost doubled after different conditions of FSP. Coefficient of friction is reduced to 1/13.3, and weight loss has been reduced to about 50% of initial values after friction stir processing. The obtained results also demonstrated the successful dynamic recrystallization during FSP.

  13. Atomic simulation of mechanical behavior of Mg in a super-lattice of nanocrystalline Mg and amorphous Mg-Al alloy

    SciTech Connect

    Song, H. Y.; An, M. R.; Li, Y. L. Deng, Q.

    2014-12-07

    The mechanical properties of a super-lattice architecture composed of nanocrystalline Mg and Mg-Al amorphous alloy are investigated using molecular dynamics simulation. The results indicate that deformation mechanism of nanocrystalline Mg is obviously affected by the amorphous boundary spacing and temperature. The strength of the material increases with the decrease of amorphous boundary spacing, presenting a Hall-Petch effect at both 10 K and 300 K. A stress platform and following stiffness softening, as well as a linear strengthening in the plastic stage, are observed when the amorphous boundary spacing below 8.792 nm at 10 K. The implying reason may be that the amorphous boundary acts as the dislocations emission and absorption source. However, the second stress peak is not observed for the models at 300 K. Instead, the flow stress in plastic stage is a nearly constant value. The simulation demonstrates the emergence of the new grain, accompanied by the deformation twins and stacking faults associated with the plastic behaviors at 300 K. The general conclusions derived from this work may provide a guideline for the design of high-performance hexagonal close-packed metals.

  14. Thermal conductivity of diethylene glycol based magnesium-aluminum spinel (MgAl2O4-DG) nanofluids

    NASA Astrophysics Data System (ADS)

    Żyła, Gaweł; Fal, Jacek; Gizowska, Magdalena; Perkowski, Krzysztof

    2016-12-01

    The paper presents the results of measurements of the thermal conductivity of MgAl_2O_4 -DG nanofluids. The dependence of the thermal conductivity on concentration of nanoparticles in various temperatures from 293.15 to 338.15 K with 15 K step was examined. Experimental data was modeled with existing theoretical models describing the effects of the concentration of particles on the thermal conductivity of the suspension. It was presented that thermal conductivity of MgAl_2O_4 -DG nanofluids increases proportional to volume concentration of nanoparticles.

  15. Thermal conductivity of diethylene glycol based magnesium-aluminum spinel (MgAl2O4-DG) nanofluids

    NASA Astrophysics Data System (ADS)

    Żyła, Gaweł; Fal, Jacek; Gizowska, Magdalena; Perkowski, Krzysztof

    2017-06-01

    The paper presents the results of measurements of the thermal conductivity of MgAl_2O_4-DG nanofluids. The dependence of the thermal conductivity on concentration of nanoparticles in various temperatures from 293.15 to 338.15 K with 15 K step was examined. Experimental data was modeled with existing theoretical models describing the effects of the concentration of particles on the thermal conductivity of the suspension. It was presented that thermal conductivity of MgAl_2O_4-DG nanofluids increases proportional to volume concentration of nanoparticles.

  16. Preparation and optimization of a drug delivery system based on berberine chloride-immobilized MgAl hydrotalcite.

    PubMed

    Djebbi, Mohamed Amine; Bouaziz, Zaineb; Elabed, Alae; Sadiki, Moulay; Elabed, Soumya; Namour, Philippe; Jaffrezic-Renault, Nicole; Amara, Abdesslem Ben Haj

    2016-06-15

    Hydrotalcite (HT), also known as a layered double hydroxide (LDH) compound, has been widely used in past years in the formulation of drugs due to its specific properties including good biocompatibility, null toxicity, high chemical stability and pH-dependent solubility which aid in drug controlled release. In this work, berberine chloride (BBC) class antibacterial agent was immobilized into magnesium-aluminum LDH in order to improve the drug efficiency as well as to achieve the controlled release property. BBC molecules were immobilized into MgAl LDH through a conventional ion exchange reaction and co-precipitation method. The ion-exchange experiments of BBC on MgAl LDH were investigated with particular attention paid to the influence of the layer charge, the nature of the intercalated anion and the morphology. The immobilization efficiency was dependent upon the LDH properties and the immobilization process. Characterization by powder x-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and contact angle measurements revealed that the interaction of BBC with MgAl LDH occurs by adsorption rather than intercalation of BBC within LDH layers. In vitro anti-bacterial tests were carried out using disc diffusion assay to prove the effectiveness of these novel biohybrid beads as a controlled drug delivery method. Consequently, the BBC-LDH co-precipitated formulation revealed an enhanced anti-bacterial activity compared to the ion-exchanged formulation not only due to an improvement of chemical stability and retained amount of BBC molecules but also due to the release property. Copyright © 2016 Elsevier B.V. All rights reserved.

  17. DFT-Based Simulation and Experimental Validation of the Topotactic Transformation of MgAl Layered Double Hydroxides.

    PubMed

    Zhang, Shi-Tong; Dou, Yibo; Zhou, Junyao; Pu, Min; Yan, Hong; Wei, Min; Evans, David G; Duan, Xue

    2016-09-05

    The thermal topotactic transformation mechanism of MgAl layered double hydroxides (LDHs) is investigated by a combined theoretical and experimental study. Thermogravimetric differential thermal analysis (TG-DTA) results reveal that the LDH phase undergoes four key endothermic events at 230, 330, 450, and 800 °C. DFT calculations show that the LDH decomposes into CO2 and residual O atoms via a monodentate intermediate at 330 °C. At 450 °C, the metal cations almost maintain their original distribution within the LDH(001) facet during the thermal dehydration process, but migrate substantially along the c-axis direction perpendicular to the (001) facet; this indicates that the metal arrangement/dispersion in the LDH matrix is maintained two-dimensionally. A complete collapse of the layered structure occurs at 800 °C, which results in a totally disordered cation distribution and many holes in the final product. The structures of the simulated intermediates are highly consistent with the observed in situ powder XRD data for the MgAl LDH sample calcined at the corresponding temperatures. Understanding the structural topotactic transformation process of LDHs would provide helpful information for the design and preparation of metal/metal oxides functional materials derived from LDH precursors.

  18. Development of a biocompatible nanodelivery system for tuberculosis drugs based on isoniazid-Mg/Al layered double hydroxide

    PubMed Central

    Saifullah, Bullo; Arulselvan, Palanisamy; El Zowalaty, Mohamed Ezzat; Fakurazi, Sharida; Webster, Thomas J; Geilich, Benjamin M; Hussein, Mohd Zobir

    2014-01-01

    The primary challenge in finding a treatment for tuberculosis (TB) is patient non-compliance to treatment due to long treatment duration, high dosing frequency, and adverse effects of anti-TB drugs. This study reports on the development of a nanodelivery system that intercalates the anti-TB drug isoniazid into Mg/Al layered double hydroxides (LDHs). Isoniazid was found to be released in a sustained manner from the novel nanodelivery system in humans in simulated phosphate buffer solutions at pH 4.8 and pH 7.4. The nanodelivery formulation was highly biocompatible compared to free isoniazid against human normal lung and 3T3 mouse fibroblast cells. The formulation was active against Mycobacterium tuberculosis and gram-positive bacteria and gram-negative bacteria. Thus results show significant promise for the further study of these nanocomposites for the treatment of TB. PMID:25336952

  19. Advantages of MgAlOx over gamma-Al2O3 as a support material for potassium-based high temperature lean NOx traps

    SciTech Connect

    Luo, Jinyong; Gao, Feng; Karim, Ayman M.; Xu, Pinghong; Browning, Nigel D.; Peden, Charles HF

    2015-08-07

    MgAlOx mixed oxides were employed as supports for potassium-based lean NOx traps (LNTs) targeted for high temperature applications. Effects of support compositions, K/Pt loadings, thermal aging and catalyst regeneration on NOx storage capacity were systematically investigated. The catalysts were characterized by XRD, NOx-TPD, TEM, STEM-HAADF and in-situ XAFS. The results indicate that MgAlOx mixed oxides have significant advantages over conventional gamma-Al2O3-supports for LNT catalysts, in terms of high temperature NOx trapping capacity and thermal stability. First, as a basic support, MgAlOx stabilizes stored nitrates (in the form of KNO3) to much higher temperatures than mildly acidic gamma-Al2O3. Second, MgAlOx minimizes Pt sintering during thermal aging, which is not possible for gamma-Al2O3 supports. Notably, combined XRD, in-situ XAFS and STEM-HAADF results indicate that Pt species in the thermally aged Pt/MgAlOx samples are finely dispersed in the oxide matrix as isolated atoms. This strong metal-support interaction stabilizes Pt and minimizes the extent of sintering. However, such strong interactions result in Pt oxidation via coordination with the support so that NO oxidation activity can be adversely affected after aging which, in turn, decreases NOx trapping ability for these catalysts. Interestingly, a high-temperature reduction treatment regenerates essentially full NOx trapping performance. In fact, regenerated Pt/K/MgAlOx catalyst exhibits much better NOx trapping performance than fresh Pt/K/Al2O3 LNTs over the entire temperature range investigated here. In addition to thermal aging, Pt/K loading effects were systemically studied over the fresh samples. The results indicate that NOx trapping is kinetically limited at low temperatures, while thermodynamically limited at high temperatures. A simple conceptual model was developed to explain the Pt and K loading effects on NOx storage. An optimized K loading, which allows balancing between the

  20. Oxidative dehydrogenation of propane over vanadia-based catalysts supported on high-surface-area mesoporous MgAl2O4

    SciTech Connect

    Evans, Owen R.; Bell, Alexis T.; Tilley, T. Don

    2004-06-01

    The oxidative dehydrogenation of propane to propene was investigated over a series of novel vanadia-based catalysts supported on high-surface-area magnesium spinel. A mesoporous MgAl2O4 support was synthesized via a low-temperature sol gel process involving the heterobimetallic alkoxide precursor, Mg[Al(O iPr)4]2. A high-purity catalyst support was obtained after calcination at 1173 K under O2 atmosphere and active vanadia catalysts were prepared from the thermolysis of OV(O tBu)3 after grafting onto the spinel support. MgAl2O4-supported catalysts prepared in this manner have BET surface areas of 234 245 m2/g. All of the catalysts were characterized by X-ray powder diffraction, and Raman, solid-state NMR, and diffuse-reflectance UV vis spectroscopy. At all vanadium loadings the vanadia supported on MgAl2O4 exist as a combination of isolated monovanadate and tetrahedral polyvanadate species. As the vanadium surface density increases for these catalysts the ratio of polyvanadate species to isolated monovanadate species increases. In addition, as the vanadium surface density increases for these catalysts, the initial rate of propane ODH per V atom increases and reaches a maximum value at 6 VOx/nm2. Increasing the vanadium surface density past this point results in a decrease in the rate of propane ODH owing to the formation of multilayer species in which subsurface vanadium atoms are essentially rendered catalytically inactive. The initial propene selectivity increases with increasing vanadium surface density and reaches a plateau of {approx}95 percent for the V/MgAl catalysts. Rate coefficients for propane ODH (k1), propane combustion (k2), and propene combustion (k3) were calculated for these catalysts. The value of k1 increases with increasing VOx surface density, reaching a maximum at about 5.5 VOx/nm2. On the other hand, the ratio (k2/k1) for V/MgAl decreases with increasing VOx surface density. The ratio (k3/k1) for both sets of catalysts shows no dependence on

  1. [A Fluorescent Chemical Sensor Based on MgAl-8-HQ LDH Composite Particle for the Selective Detection of Fe3+].

    PubMed

    Yang, Lei; Yao, Qi; Yuan, Xue-hua; Yang, Yan-ling

    2015-03-01

    In order to achieve the highly selective and Simple detection for ferric ion, strong-fluorescent 8-hydroxyquinoline (8-HQ) Mg-Al layered double hydroxide(Mg(χ)Al-8-HQ LDH) was designed and prepared by 8-HQ's intercalation and ready coordination based on adjustment of Al3+ on Mg-Al layered double hydroxides (MgAl LDH) laminates. Meanwhile its structure and property were characterized by IR, XRD, UV-Vis and fluorescent spectrometer. IR analysis showed coordinate bonds of C-O-Al and C-N-Al between 8-HQ and Al3+ were generated. XRD revealed that 8-HQ had already inserted in MgAl LDH laminates, and it made (003) diffraction peaks move to low 2θ angle direction, and the diffraction peak intensity was enhanced with the molar ratio of Mg and Al increasing. Because the coordination reaction between 8-HQ and Al3+ in MgAl LDH laminates took place, it induced the absorption peak of 8-HQ at 314 nm disappeared, at the same time the transition absorption peak at 376 nm between metal ions and ligands appeared. As demonstrated by fluorescence spectroscopic analysis, fluorescence intensity of Mg(χ)Al-8-HQ LDH increased with the content of Al3+ reducing, when the molar ratio of Magnesium and Aluminium ion is 4 : 1, its fluorescence intensity enhanced more significantly than 8-hydroxyquinoline aluminum. Through the research on the influence of metal ions on the fluorescence spectra of Mg4 Al-8-HQ LDH particle, it was found that the particle to metal ions exhibited significant selection and difference, especially with high selectivity for Fe3+ ion. The effect of [Fe3+] on the color and fluorescence intensity of Mg4Al-8-HQ LDH particle solution was further studied, and the results showed that the solution varied from light yellow to dark green with the content of Fe3+ in 10(-6) to 10(-2) mol x L(-1) increasing, so it can implement colorimetric sensing for Fe3+ in the above range. And at the same time its fluorescence intensity significantly decreased, and its fluorescence could be

  2. Fe/Co alloys for the catalytic chemical vapor deposition synthesis of single- and double-walled carbon nanotubes (CNTs). 2. The CNT-Fe/Co-MgAl2O4 system.

    PubMed

    Coquay, Pierre; Flahaut, Emmanuel; De Grave, Eddy; Peigney, Alain; Vandenberghe, Robert E; Laurent, Christophe

    2005-09-29

    A detailed 57Fe Mössbauer study of the Mg(0.8)Fe(0.2-y)Co(y)Al2O4 (y = 0, 0.05, 0.1, 0.15, 0.2) solid solutions and of the CNT-Fe/Co-MgAl2O4 nanocomposite powders prepared by reduction in H2-CH4 has allowed characterization of the different iron phases involved in the catalytic process of carbon nanotube (CNT) formation and to correlate these results with the carbon and CNT contents. The oxide precursors consist of defective spinels of general formulas (Mg(1-x-y)(2+)Fe(x-3alpha)(2+)Fe(2alpha)(3+)[symbol: see text](alpha)Co(y)(2+)Al2(3+))O4(2-) . The metallic phase in the CNT-Fe/Co-MgAl2O4 nanocomposite powders is mostly in the form of the ferromagnetic alpha-Fe/Co alloy with the desired composition. For high iron initial proportions, the additional formation of Fe3C and gamma-Fe-C is observed while for high cobalt initial proportions, the additional formation of a gamma-Fe/Co-C phase is favored. The higher yield of CNTs is observed for postreaction alpha-Fe(0.50)Co(0.50) catalytic particles, which form no carbide and have a narrow size distribution. Alloying is beneficial for this system with respect to the formation of CNTs.

  3. Phosphate adsorption ability of biochar/Mg-Al assembled nanocomposites prepared by aluminum-electrode based electro-assisted modification method with MgCl₂ as electrolyte.

    PubMed

    Jung, Kyung-Won; Jeong, Tae-Un; Hwang, Min-Jin; Kim, Kipal; Ahn, Kyu-Hong

    2015-12-01

    In this work, the textural properties and phosphate adsorption capability of modified-biochar containing Mg-Al assembled nanocomposites prepared by an effective electro-assisted modification method with MgCl2 as an electrolyte have been determined. Structure and chemical analyses of the modified-biochar showed that nano-sized stonelike or flowerlike Mg-Al assembled composites, MgO, spinel MgAl2O4, AlOOH, and Al2O3, were densely grown and uniformly dispersed on the biochar surface. The adsorption isotherm and kinetics data suggested that the biochar/Mg-Al assembled nanocomposites have an energetically heterogeneous surface and that phosphate adsorption could be controlled by multiple processes. The maximum phosphate adsorption capacity was as high as 887 mg g(-1), as fitted by the Langmuir-Freundlich model, and is the highest value ever reported. It was concluded that this novel electro-assisted modification is a very attractive method and the biochar/Mg-Al assembled nanocomposites provide an excellent adsorbent that can effectively remove phosphate from aqueous solutions. Copyright © 2015 Elsevier Ltd. All rights reserved.

  4. Effect of Mg-Al insertion on magnetotransport properties in epitaxial Fe/sputter-deposited MgAl2O4/Fe(001) magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

    We investigated the effect of an Mg-Al layer insertion at the bottom interface of epitaxial Fe/MgAl2O4/Fe(001) magnetic tunnel junctions (MTJs) on their spin-dependent transport properties. The tunnel magnetoresistance (TMR) ratio and differential conductance spectra for the parallel magnetic configuration exhibited clear dependence on the inserted Mg-Al thickness. A slight Mg-Al insertion (thickness < 0.1 nm) was effective for obtaining a large TMR ratio above 200% at room temperature and observing a distinct local minimum structure in conductance spectra. In contrast, thicker Mg-Al (> 0.2 nm) induced a reduction of TMR ratios and featureless conductance spectra, indicating a degradation of the bottom-Fe/MgAl2O4 interface. Therefore, a minimal Mg-Al insertion was found to be effective to maximize the TMR ratio for a sputtered MgAl2O4-based MTJ.

  5. The development of lightweight hydride alloys based on magnesium

    SciTech Connect

    Guthrie, S.E.; Thomas, G.J.; Yang, N.Y.C.; Bauer, W.

    1996-02-01

    The development of a magnesium based hydride material is explored for use as a lightweight hydrogen storage medium. It is found that the vapor transport of magnesium during hydrogen uptake greatly influences the surface and hydride reactions in these alloys. This is exploited by purposely forming near-surface phases of Mg{sub 2}Ni on bulk Mg-Al-Zn alloys which result in improved hydrogen adsorption and desorption behavior. Conditions were found where these near-surface reactions yielded a complex and heterogeneous microstructure that coincided with excellent bulk hydride behavior. A Mg-Al alloy hydride is reported with near atmospheric plateau pressures at temperatures below 200{degrees}C. Additionally, a scheme is described for low temperature in-situ fabrication of Mg{sub 2}Ni single phase alloys utilizing the high vapor pressure of Mg.

  6. Prediction and characterization of an Mg-Al intermetallic compound with potentially improved ductility via orbital-free and Kohn-Sham density functional theory

    NASA Astrophysics Data System (ADS)

    Zhuang, Houlong L.; Chen, Mohan; Carter, Emily A.

    2017-10-01

    Magnesium-aluminum (Mg-Al) intermetallic compounds that form as precipitates can significantly influence the mechanical properties of Mg-Al alloys. A computational evaluation of known and unknown Mg-Al intermetallic compounds could help design new Mg-Al alloy microstructures with optimal properties. Here, we employ the cluster-expansion method with energies efficiently calculated with orbital-free density functional theory (OFDFT) and predict a new, metastable intermetallic compound Mg3Al with a D019 hexagonal structure that is slightly more stable than an alternative L12 cubic structure. We apply Kohn-Sham DFT (KSDFT) to accurately evaluate various metastability criteria for D019 and L12 Mg3Al, including Born’s criterion and phonon dispersion. We show that both Mg3Al crystalline phases satisfy the metastability criteria and hence should be at least metastable. We further compare ductility metrics for D019 and L12 Mg3Al to that of hexagonal-close-packed Mg by computing Pugh’s ratio and generalized stacking fault energies. The ductility is predicted to follow the order: D019 Mg3Al > L12 Mg3Al > Mg, based on the highest Pugh’s ratio and the lowest unstable stacking and twinning fault energies of D019 Mg3Al compared to that of Mg. We also predict a very low antiphase boundary energy for Mg3Al and therefore expect D019 Mg3Al to be beneficial for improving the ductility of Mg-rich Mg-Al alloys. A computational design of Mg-Al alloy microstructures may become possible by combining the strengths of both OFDFT and KSDFT, i.e., the efficiency of the former and the accuracy of the latter, as demonstrated here.

  7. SUPERCONDUCTING VANADIUM BASE ALLOY

    DOEpatents

    Cleary, H.J.

    1958-10-21

    A new vanadium-base alloy which possesses remarkable superconducting properties is presented. The alloy consists of approximately one atomic percent of palladium, the balance being vanadium. The alloy is stated to be useful in a cryotron in digital computer circuits.

  8. Influence of the presence of ruthenium on the activity and stability of Co-Mg-Al-based catalysts in CO2 reforming of methane for syngas production.

    PubMed

    Gennequin, Cédric; Hany, Sara; Tidahy, Haingomalala Lucette; Aouad, Samer; Estephane, Jane; Aboukaïs, Antoine; Abi-Aad, Edmond

    2016-11-01

    Hydrogen production by methane dry reforming is an important yet challenging process. A performing catalyst will favor the thermodynamic equilibrium while ensuring good hydrogen selectivity. We hereby report the synthesis of Co x Mg6-x Al2 (with x = 2 and 6) mixed oxide catalysts synthesized via hydrotalcite precursors and the synthesis of a ruthenium-based catalyst on a cobalt, magnesium, and aluminum mixed oxide supports Ru/Co x Mg6-x Al2 (with x = 2 and 6). The impregnation of ruthenium on the hydrotalcites was performed in two ways: by impregnation on the dried hydrotalcite and by memory effect on hydrotalcite calcined at 500 °C. The deposition of ruthenium by memory effect of the magnesium and cobalt support allows the generation of both metallic and basic sites which provides an active and stable catalyst for the dry reforming reaction of methane.

  9. 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.

  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

    2016-06-01

    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.

  11. 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

  12. 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.

  13. NICKEL-BASE ALLOY

    DOEpatents

    Inouye, H.; Manly, W.D.; Roche, T.K.

    1960-01-19

    A nickel-base alloy was developed which is particularly useful for the containment of molten fluoride salts in reactors. The alloy is resistant to both salt corrosion and oxidation and may be used at temperatures as high as 1800 deg F. Basically, the alloy consists of 15 to 22 wt.% molybdenum, a small amount of carbon, and 6 to 8 wt.% chromium, the balance being nickel. Up to 4 wt.% of tungsten, tantalum, vanadium, or niobium may be added to strengthen the alloy.

  14. First-principles determination of crystal structures, phase stability, and reaction thermodynamics in the Li-Mg-Al-H hydrogen storage system

    NASA Astrophysics Data System (ADS)

    Akbarzadeh, A. R.; Wolverton, C.; Ozolins, V.

    2009-05-01

    First-principles density-functional theory (DFT) calculations have been used to investigate the crystal structures, thermodynamic stability, and decomposition pathways of Li-Mg-Al-H hydrogen storage compounds. We find that the recently discovered LiMg(AlH4)3 compound is stable with respect to solid-state decomposition into LiAlH4 and Mg(AlH4)2 ; however, we also find that LiMg(AlH4)3 is unstable with respect to hydrogen release and decomposes exothermically into LiMgAlH6 , Al, and H2 with a calculated T=300K enthalpy of -7.3kJ/(molH2) , in excellent agreement with the weakly exothermic value of -5kJ/(molH2) obtained from differential scanning calorimetry measurements [M. Mamatha , J. Alloys Compd. 407, 78 (2006)]. LiMgAlH6 is a stable intermediate, which has two competing endothermic decomposition pathways for H2 release: one going directly into the binary hydrides of Li and Mg and the other proceeding via the formation of an intermediate Li3AlH6 phase, with room-temperature enthalpies of +18.6 and +16.6kJ/(molH2) , respectively. Using database searching based on known crystal structures from the inorganic crystal structure database, we predict that the hypothetical MgAlH5 compound should assume the orthorhombic BaGaF5 prototype structure, in contrast to a previous DFT study of MgAlH5 , [A. Klaveness , Phys. Rev. B 73, 094122 (2006)]. However, the decomposition enthalpy of MgAlH5 is only weakly endothermic, +1.1kJ/(molH2) , and therefore this compound is not expected to occur in the high-temperature decomposition sequence of Mg alanate. We also present a comprehensive investigation of the phonon spectra and vibrational thermodynamics of Li-Mg-Al-H compounds, finding that vibrations typically decrease reaction enthalpies by up to 10kJ/molH2 at ambient temperatures and significantly lower reaction entropies.

  15. TUNGSTEN BASE ALLOYS

    DOEpatents

    Schell, D.H.; Sheinberg, H.

    1959-12-15

    A high-density quaternary tungsten-base alloy having high mechanical strength and good machinability composed of about 2 wt.% Ni, 3 wt.% Cu, 5 wt.% Pb, and 90wt.% W is described. This alloy can be formed by the powder metallurgy technique of hot pressing in a graphite die without causing a reaction between charge and the die and without formation of a carbide case on the final compact, thereby enabling re-use of the graphite die. The alloy is formable at hot- pressing temperatures of from about 1200 to about 1350 deg C. In addition, there is little component shrinkage, thereby eliminating the necessity of subsequent extensive surface machining.

  16. 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.

  17. Elastic and Thermodynamic Properties of Complex Mg-Al Intermetallic Compounds via Orbital-Free Density Functional Theory

    NASA Astrophysics Data System (ADS)

    Zhuang, Houlong; Chen, Mohan; Carter, Emily A.

    2016-06-01

    Magnesium-aluminum (Mg-Al) alloys are important metal alloys with a wide range of engineering applications. We investigate the elastic and thermodynamic properties of Mg, Al, and four stoichiometric Mg-Al compounds including Mg17Al12 , Mg13Al14 , and Mg23Al30 , and MgAl2 with orbital-free density-functional theory (OFDFT). We first calculate the lattice constants, zero-temperature formation energy, and independent elastic constants of these six materials and compare the results to those computed via Kohn-Sham DFT (KSDFT) benchmarks. We obtain excellent agreement between these two methods. Our calculated elastic constants of hexagonal close-packed Mg and face-centered-cubic Al are also consistent with available experimental data. We next compute their phonon spectra using the force constants extracted from the very fast OFDFT calculations, because such calculations are computationally challenging using KSDFT. This is especially the case for the Mg23Al30 compound, whose 3 ×3 ×3 supercell consists of 1431 atoms. We finally employ the quasiharmonic approximation to investigate temperature-dependent thermodynamic properties, including formation energies, heat capacities, and thermal expansion of the four Mg-Al intermetallic compounds. The calculated heat capacity and thermal expansion of both Mg and Al agree well with experimental data. We additionally find that Mg13Al14 and MgAl2 are both unstable, consistent with their absence from the equilibrium Mg-Al phase diagram. Our work demonstrates that OFDFT is an efficient and accurate quantum-mechanical computational tool for predicting elastic and thermodynamic properties of complicated Mg-Al alloys and also should be applicable to many other engineering alloys.

  18. 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

  19. 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.

  20. 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.

  1. Investigation of fluorine adsorption on nitrogen doped MgAl2O4 surface by first-principles

    NASA Astrophysics Data System (ADS)

    Lv, Xiaojun; Xu, Zhenming; Li, Jie; Chen, Jiangan; Liu, Qingsheng

    2016-07-01

    The nature of fluorine adsorption on pure and N doped MgAl2O4 surface has been investigated by first-principles calculations based on the density functional theory. Calculated results indicate that MgAl2O4 surface is fluorine-loving, not hydrophilic. Nitrogen doped MgAl2O4 (100) surface shows the highest fluorine adsorption performance and fluorine atom preferentially adsorbs on the Mg-Al bridge site. The fluorine adsorption intensity follow this order: Nitrogen doped MgAl2O4 (100) > Al2O3 (0001) > MgAl2O4 (100) > MgO (100). In-depth PDOS analysis suggested that 2p orbitals of F atom strongly hybridized with 3s- and 3p-orbitals of Al atom contribute to its high adsorption intensity. According to the analysis of Hirshfeld charge, the excellent fluorine adsorption performance of nitrogen doped MgAl2O4 attributes to the electron compensation effect of nitrogen atom and strong electrostatic interactions. All these evidences demonstrate a fact nitrogen doped MgAl2O4 is a promising candidate for fluorine removal.

  2. Removal of boron and fluoride in wastewater using Mg-Al layered double hydroxide and Mg-Al oxide.

    PubMed

    Kameda, Tomohito; Oba, Jumpei; Yoshioka, Toshiaki

    2017-03-01

    Mg-Al layered double hydroxide intercalated with NO3(-) and Mg-Al oxide were found to remove hazardous materials such as B and As, as well as Cl(-) and SO4(2-), from artificial and real hot spring wastewater. However, compared with the mixture of Al2(SO4)3 and Ca(OH)2, both adsorbents were inferior for the removal of B from real hot spring wastewater. Both adsorbents were also found to remove F(-) and PO4(3-) from artificial semiconductor plant wastewater. Both adsorbents have the same ability to remove B from landfill wastewater as the mixture of Al2(SO4)3 and Ca(OH)2; furthermore, both remove Cl(-), Br(-), and SO4(2-). The benefit of Mg-Al layered double hydroxide intercalated with NO3(-) is that it does not require neutralization after the treatment. Overall, it can be stated that among the materials tested, Mg-Al layered double hydroxide intercalated with NO3(-) is the most suitable adsorbent for the treatment of hot spring and landfill wastewater.

  3. Tissue Response to Base-Metal Dental Alloys.

    DTIC Science & Technology

    RESPONSE(BIOLOGY), *CASTING ALLOYS, *BASE METAL, * DENTAL PROSTHESES, TISSUES(BIOLOGY), COMPATIBILITY, NICKEL ALLOYS, BERYLLIUM, DENTISTRY, CANCER, HISTOLOGY, DENTAL IMPLANTOLOGY , COBALT ALLOYS, CHROMIUM ALLOYS.

  4. Thermoluminescence of K-Mg-Al-Zn fluorophosphate glass

    NASA Astrophysics Data System (ADS)

    Thomas, Sunil; Chithambo, M. L.

    2017-02-01

    The thermoluminescence of beta irradiated K-Mg-Al-Zn fluorophosphate glass is reported. A glow-curve corresponding to 10 Gy measured at 1 °C/s shows two peaks, a weaker-intensity one at 70 °C and a more prominent one at 235 °C, the subject of this report. The main peak was observed to fade with delay between irradiation and measurement and specifically, by 11% in 15 h. Its dose response is superlinear in the dose range 1-190 Gy although the change was linear for the initial 10 Gy. Regarding kinetic analysis, the activation energy of the higher temperature peak was evaluated as 1.31 eV and that of the lower temperature peak was found as 0.47 eV. It was also noted that the main peak is affected by thermal quenching with an activation energy for thermal quenching equal to 1.37 eV. It is proposed that the mechanism associated with the thermoluminescence in K-Mg-Al-Zn fluorophosphate glass is that electrons trapped by the metal cations are released during heating and then recombine with holes at oxygen sites.

  5. Controlled release of ibuprofen using Mg Al LDH nano carrier

    NASA Astrophysics Data System (ADS)

    Dasgupta, Sudip

    2017-08-01

    In the present study, NSAID (non-steroidal anti-inflammatory drugs) such as ibuprofen in anionic form has been intercalated in-situ into the interlayer space of Mg Al LDH nanoparticle during co-precipitation of hydroxides. LDH nanohybrids are characterized by XRD, FTIR and UV spectroscopy. Mg1-xAlx(NO3)x(OH)2.nH2O nanoparticles were synthesized using co-precipitation method from an aqueous solution of Mg(NO3)2.6H2O and Al(NO3)3.9H2O. Ibuprofen was intercalated in inter layer space of Mg-Al LDH during coprecipitation of drug LDH conjugate in nitrogen atmosphere. The nanopowders synthesised were in the size range between 25 to 90 nm with an average particle size of 55 nm. XRD analysis proved that there is an increase in d003 spacing from 7.89 Å for pristine LDH to 14.71 Å for ibuprofen intercalated LDH due to the intercalation of bigger ibuprofen molecule in the interlayer space of LDH. FTIR analysis showed hydroxyl and carbonyl stretching of ibuprofen in LDH-IBU sample confirming the intercalation of ibuprofen in the interlayer structure of LDH. The drug release study in phosphate buffer solution at pH 7.4 using UV-Vis spectroscopy demonstrated that 50 % drug molecules were released in 15 hours and more than 85 % release was achieved after 36 hours.

  6. Influence of Zn Interlayer on Interfacial Microstructure and Mechanical Properties of TIG Lap-Welded Mg/Al Joints

    NASA Astrophysics Data System (ADS)

    Gao, Qiong; Wang, Kehong

    2016-03-01

    This study explored 6061 Al alloy and AZ31B Mg alloy joined by TIG lap welding with Zn foils of varying thicknesses, with the additional Zn element being imported into the fusion zone to alloy the weld seam. The microstructures and chemical composition in the fusion zone near the Mg substrate were examined by SEM and EDS, and tensile shear strength tests were conducted to investigate the mechanical properties of the Al/Mg joints, as well as the fracture surfaces, and phase compositions. The results revealed that the introduction of an appropriate amount of Zn transition layer improves the microstructure of Mg/Al joints and effectively reduces the formation of Mg-Al intermetallic compounds (IMCs). The most common IMCs in the fusion zone near the Mg substrate were Mg-Zn and Mg-Al-Zn IMCs. The type and distribution of IMCs generated in the weld zone differed according to Zn additions; Zn interlayer thickness of 0.4 mm improved the sample's mechanical properties considerably compared to thicknesses of less than 0.4 mm; however, any further increase in Zn interlayer thickness of above 0.4 mm caused mechanical properties to deteriorate.

  7. Millimeter-Wavelength Radiation Used to Sinter Radiotransparent MgAl2O4 Ceramics

    NASA Astrophysics Data System (ADS)

    Egorov, S. V.; Bykov, Yu. V.; Eremeev, A. G.; Sorokin, A. A.; Serov, E. A.; V. Parshin, V.; S. Balabanov, S.; Belyaev, A. V.; V. Novikova, A.; Permin, D. A.

    2017-01-01

    We have developed a method for production of high-density MgAl2O4 ceramics characterized by low dielectric losses. The method is based on sintering of ultrafine, high-purity powder materials in the electromagnetic field of intense microwave radiation. The initial nanodimensional magnesium-aluminate powder was synthesized by the sol-gel method and sintered in a gyrotron complex operated at a frequency of 24 GHz. The results of studying the conditions and regimes of microwave sintering of MgAl2O4 ceramics are presented, along with its phase features, microstructural peculiarities, and mechanical and dielectric characteristics. The possibility of controlling the microstructure of the sintered material by varying the regime of RF heating is demonstrated.

  8. Characteristics of Pt-K/MgAl2O4 lean NOx trap catalysts

    SciTech Connect

    Kim, Do Heui; Mudiyanselage, Kumudu K.; Szanyi, Janos; Zhu, Haiyang; Kwak, Ja Hun; Peden, Charles HF

    2012-04-30

    We report the various characteristics of Pt-K/MgAl{sub 2}O{sub 4} lean NOx trap (LNT) catalysts including the effect of K loading on nitrate formation/decomposition, NOx storage activity and durability. Upon the adsorption of NO{sub 2} on K/MgAl{sub 2}O{sub 4} samples, potassium nitrates formed on Mg-related sites in MgAl{sub 2}O{sub 4} support are observed, in addition to the typical two potassium nitrates (ionic and bidentate) formed also on Al{sub 2}O{sub 3} supported sample. Based on NO{sub 2} TPD and FTIR results, the Mg-bound KNO{sub 3} thermally decompose at higher temperature than Al-bound KNO{sub 3}, implying its superior thermal stability. At a potassium loading of 5wt%, the temperature of maximum NOx uptake (T{sub max}) is 300 C. Increasing the potassium loading from 5wt% to 10 wt%, the T{sub max} gradually shifted from 300 C to 450 C, indicating the dependence of T{sub max} on the potassium loading. However, increase in potassium loading above 10 wt% only gives rise to the reduction in the overall NOx storage capacity. This work also underlines the obstacles these materials have prior to their practical application (e.g., durability and sulfur poisoning/ removal). This work provides fundamental understanding of Pt-K/MgAl{sub 2}O{sub 4}-based lean NOx trap catalysts, which could be good candidates for high temperature LNT applications.

  9. High strength forgeable tantalum base alloy

    NASA Technical Reports Server (NTRS)

    Buckman, R. W., Jr.

    1975-01-01

    Increasing tungsten content of tantalum base alloy to 12-15% level will improve high temperature creep properties of existing tantalum base alloys while retaining their excellent fabrication and welding characteristics.

  10. Structure and surface and catalytic properties of Mg-Al basic oxides

    SciTech Connect

    Cosimo, J.I.D.; Diez, V.K.; Apesteguia, C.R.; Xu, M.; Iglesia, E.

    1998-09-10

    Mg-Al mixed oxides with Mg/Al molar ratios of 0.5--9.0 were obtained by thermal decomposition of precipitated hydrotalcite precursors. The effect of composition on structure and surface and catalytic properties was studied by combining several characterization methods with ethanol conversion reactions. The nature, density, and strength of surface basic sites depended on the Al content. The catalyst activity and selectivity of Mg-Al mixed oxides in ethanol conversion reactions depended on composition. The dehydrogenation of ethanol to acetaldehyde and the aldol condensation to n-butanol both involved the initial surface ethoxide formation on a Lewis acid-strong base pair. The dehydration of ethanol to ethylene, and the coupling and dehydration to diethyl ether increased with Al content, probably reflecting the density increase of both Al{sup 3+}-O{sup 2{minus}} pairs and low- and medium-strength basic sites. Pure Al{sub 2}O{sub 3} displayed the highest dehydration activity.

  11. Preparation of Mg/Al-LDHs intercalated with dodecanoic acid and investigation of its antiwear ability

    SciTech Connect

    Zhao, Dong; Bai, Zhimin; Zhao, Fuyan

    2012-11-15

    Graphical abstract: Comparable studies of nano Mg/Al-LDHs powder on the anti-wear properties of lubricating oil were carried out on four-ball and gear testing machine. Mg/Al-NO{sub 3}{sup −}-LDHs and Mg/Al-DA-LDHs powder in base oil possess an excellent friction-reducing property, with a friction coefficient at 23.9% and 22.2% which are lower than that of the base oil Highlights: ► We synthesized nano Mg/Al-NO{sub 3}{sup −}(DA)-LDHs via coprecipitation and anion exchange. ► The optimal exchanging condition is as follows: water dispersion and pH value of 5. ► The tribological properties of LDHs were studied on four-ball and gear machine. ► We reported nano LHDs as anti-wear materials in lubricates for the first time. ► The greatest decline in friction coefficient of lubricates with LDHs is up to 23.9%. -- Abstract: Layered double hydroxides (LDHs) intercalated with dodecanoic acid have been prepared by anion exchange with Mg/Al-NO{sub 3}{sup −}-LDHs as the precursor under acid condition with water and ethanol as the dispersion medium. The obtained materials were characterized by X-ray diffraction (XRD), thermogravimetric and differential thermal analyser (TG–DTA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and BET. Patterns of XRD and FTIR show that interlayer nitrate ions have substituted with dodecanoic acid and the gallery height has increased from 0.88 nm to 1.99 nm. The interlayer distance of the intercalated materials increases with the increase of pH value due to the different arrangement of interlayer anions. The tribological performance of LDHs precursor and intercalated LDHs in base oil were studied for the first time by using four-ball wear machine and gear testing machine. Experimental results show that the LDHs precursor and intercalated LDHs powder are excellent in friction-reducing, with decreases in friction coefficient by 23.9% and 22.2% respectively comparing with base oil.

  12. 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.

  13. Feasibility study of the direct mechano-chemical synthesis of nanostructured magnesium tetrahydroaluminate (alanate) [Mg(AlH(4))(2)] complex hydride.

    PubMed

    Varin, R A; Chiu, Ch; Czujko, T; Wronski, Z

    2005-10-01

    The present work reports a feasibility study of the direct mechano-chemical synthesis by controlled reactive mechanical alloying (CRMA) in a magneto-ball mill of the nanostructured magnesium tetrahydroaluminate (magnesium alanate) Mg(AlH(4))(2) complex hydride. Three stoichiometric Mg-2Al mixtures, (a) elemental Mg and Al powders, (b) elemental Al powder and commercial AZ91 alloy (Mg-Al-Zn alloy) and (c) powder of as-cast Mg-2Al alloy, have been used. No successful synthesis of Mg(AlH(4))(2) has been achieved. The only nanocrystalline hydride formed up to 270 h of CRMA is beta-MgH(2), and it does not react with Al and H(2) to form Mg(AlH(4))(2). It has been found that there is strong competition between formation of Al(Mg) solid solution and the beta-MgH(2) hydride occurring to a various extent up to approximately 10 h of CRMA in all three Mg-2Al mixtures. It is hypothesized that the presence of Al(Mg) solid solution inhibits the reaction of beta-MgH(2), Al and H(2) to form Mg(AlH(4))(2). Furthermore, despite the fact that after prolonged milling the Al(Mg) solution eventually decomposes into secondary Al(s) (derived from solid solution), the latter retains its physico-chemical characteristics of the former solid solution which still inhibits the reaction to form Mg(AlH(4))(2). Experimental evidence from DSC measurements shows increasing ranges of the melting enthalpy with increasing amounts of Al(Mg) solid solution and consequently the secondary Al(s) for all the three Mg-2Al mixtures. This strongly supports the hypothesis about the different nature of Al(Mg) and the secondary Al(s) as compared to the primary elemental Al powder.

  14. 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.

  15. Removal of SO2 with a Mg-Al oxide slurry via reconstruction of a Mg-Al layered double hydroxide.

    PubMed

    Kameda, Tomohito; Kodama, Aki; Fubasami, Yuki; Kumagai, Shogo; Yoshioka, Toshiaki

    2012-06-01

    Although effective treatments of SO(x) are essential for preventing air pollution, current methods pose other environmental problems such as increased amounts of desulfurized gypsum and reduced landfill lifetimes. We report a process for removing SO(2) from waste streams using a Mg-Al oxide slurry. The ability of the mixed oxide to remove SO(2) increased with slurry quantity and temperature but decreased with time. SO(2) was removed through the reconstruction of a Mg-Al layered double hydroxide (Mg-Al LDH) intercalated with SO(3)(2-), which was derived from the dissociation of H(2)SO(3) upon dissolution of SO(2) in the slurry. SO(2) was not adsorbed onto the surface of the Mg-Al oxide. These results suggest that SO(2) removal using a Mg-Al oxide slurry may be possible without the concomitant problems of conventional treatment methods.

  16. Nanoporous composites prepared by a combination of SBA-15 with Mg-Al mixed oxides. Water vapor sorption properties.

    PubMed

    Pérez-Verdejo, Amaury; Sampieri, Alvaro; Pfeiffer, Heriberto; Ruiz-Reyes, Mayra; Santamaría, Juana-Deisy; Fetter, Geolar

    2014-01-01

    This work presents two easy ways for preparing nanostructured mesoporous composites by interconnecting and combining SBA-15 with mixed oxides derived from a calcined Mg-Al hydrotalcite. Two different Mg-Al hydrotalcite addition procedures were implemented, either after or during the SBA-15 synthesis (in situ method). The first procedure, i.e., the post-synthesis method, produces a composite material with Mg-Al mixed oxides homogeneously dispersed on the SBA-15 nanoporous surface. The resulting composites present textural properties similar to the SBA-15. On the other hand, with the second procedure (in situ method), Mg and Al mixed oxides occur on the porous composite, which displays a cauliflower morphology. This is an important microporosity contribution and micro and mesoporous surfaces coexist in almost the same proportion. Furthermore, the nanostructured mesoporous composites present an extraordinary water vapor sorption capacity. Such composites might be utilized as as acid-base catalysts, adsorbents, sensors or storage nanomaterials.

  17. Microstructural development in Al/MgAl2O4 in situ metal matrix composite using value-added silica sources

    PubMed Central

    Madathil Sreekumar, Vadakke; Marimuthu Pillai, Raman; Chandrasekhara Pai, Bellampettu; Chakraborty, Madhusudhan

    2008-01-01

    Al/MgAl2O4 in situ metal matrix composites have been synthesized using value-added silica sources (microsilica and rice husk ash) containing ∼97% SiO2 in Al-5 wt.% Mg alloy. The thermodynamics and kinetics of MgAl2O4 formation are discussed in detail. The MgO and MgAl2O4 phases were found to dominate in microsilica (MS) and rice husk ash (RHA) value-added composites, respectively, during the initial stage of holding the composites at 750 °C. A transition phase between MgO and MgAl2O4 was detected by the scanning electron microscopy and energy-dispersive spectroscopy (SEM–EDS) analysis of the particles extracted from the composite using 25% NaOH solution. This confirms that MgO is gradually transformed to MgAl2O4 by the reaction 3SiO2(s)+2MgO(s)+4Al(l)→2MgAl2O4(s)+3Si(l). The stoichiometry of MgAl2O4, n, computed by a new methodology is between 0.79 and 1.18. The reaction between the silica sources and the molten metal stopped after 55% of the silica source was consumed. A gradual increase in mean MgAl2O4 crystallite size, D, from 24 to 36 nm was observed in the samples held for 10 h. PMID:27877941

  18. Microstructural development in Al/MgAl2O4in situ metal matrix composite using value-added silica sources.

    PubMed

    Madathil Sreekumar, Vadakke; Marimuthu Pillai, Raman; Chandrasekhara Pai, Bellampettu; Chakraborty, Madhusudhan

    2008-01-01

    Al/MgAl2O4in situ metal matrix composites have been synthesized using value-added silica sources (microsilica and rice husk ash) containing ∼97% SiO2 in Al-5 wt.% Mg alloy. The thermodynamics and kinetics of MgAl2O4 formation are discussed in detail. The MgO and MgAl2O4 phases were found to dominate in microsilica (MS) and rice husk ash (RHA) value-added composites, respectively, during the initial stage of holding the composites at 750 °C. A transition phase between MgO and MgAl2O4 was detected by the scanning electron microscopy and energy-dispersive spectroscopy (SEM-EDS) analysis of the particles extracted from the composite using 25% NaOH solution. This confirms that MgO is gradually transformed to MgAl2O4 by the reaction 3SiO2(s)+2MgO(s)+4Al(l)→2MgAl2O4(s)+3Si(l). The stoichiometry of MgAl2O4, n, computed by a new methodology is between 0.79 and 1.18. The reaction between the silica sources and the molten metal stopped after 55% of the silica source was consumed. A gradual increase in mean MgAl2O4 crystallite size, D, from 24 to 36 nm was observed in the samples held for 10 h.

  19. Synthesis of Pt/K2CO3/MgAlOx–reduced graphene oxide hybrids as promising NOx storage–reduction catalysts with superior catalytic performance

    PubMed Central

    Mei, Xueyi; Yan, Qinghua; Lu, Peng; Wang, Junya; Cui, Yuhan; Nie, Yu; Umar, Ahmad; Wang, Qiang

    2017-01-01

    Pt/K2CO3/MgAlOx–reduced graphene oxide (Pt/K/MgAlOx–rGO) hybrids were synthesized, characterized and tested as a promising NOx storage and reduction (NSR) catalyst. Mg–Al layered double hydroxides (LDHs) were grown on rGO via in situ hydrothermal crystallization. The structure and morphology of samples were thoroughly characterized using various techniques. Isothermal NOx adsorption tests indicated that MgAlOx–rGO hybrid exhibited better NOx trapping performance than MgAlOx, from 0.44 to 0.61 mmol · g−1, which can be attributed to the enhanced particle dispersion and stabilization. In addition, a series of MgAlOx–rGO loaded with 2 wt% Pt and different loadings (5, 10, 15, and 20 wt%) of K2CO3 (denoted as Pt/K/MgAlOx–rGO) were obtained by sequential impregnation. The influence of 5% H2O on the NOx storage capacity of MgAlOx–rGO loaded with 2 wt% Pt and 10% K2CO3 (2Pt/10 K/MgAlOx–rGO) catalyst was also evaluated. In all, the 2Pt/10 K/MgAlOx–rGO catalyst not only exhibited high thermal stability and NOx storage capacity of 1.12 mmol · g−1, but also possessed excellent H2O resistance and lean–rich cycling performance, with an overall 78.4% of NOx removal. This work provided a new scheme for the preparation of highly dispersed MgAlOx–rGO hybrid based NSR catalysts. PMID:28205630

  20. Synthesis of Pt/K2CO3/MgAlOx–reduced graphene oxide hybrids as promising NOx storage–reduction catalysts with superior catalytic performance

    NASA Astrophysics Data System (ADS)

    Mei, Xueyi; Yan, Qinghua; Lu, Peng; Wang, Junya; Cui, Yuhan; Nie, Yu; Umar, Ahmad; Wang, Qiang

    2017-02-01

    Pt/K2CO3/MgAlOx–reduced graphene oxide (Pt/K/MgAlOx–rGO) hybrids were synthesized, characterized and tested as a promising NOx storage and reduction (NSR) catalyst. Mg–Al layered double hydroxides (LDHs) were grown on rGO via in situ hydrothermal crystallization. The structure and morphology of samples were thoroughly characterized using various techniques. Isothermal NOx adsorption tests indicated that MgAlOx–rGO hybrid exhibited better NOx trapping performance than MgAlOx, from 0.44 to 0.61 mmol · g‑1, which can be attributed to the enhanced particle dispersion and stabilization. In addition, a series of MgAlOx–rGO loaded with 2 wt% Pt and different loadings (5, 10, 15, and 20 wt%) of K2CO3 (denoted as Pt/K/MgAlOx–rGO) were obtained by sequential impregnation. The influence of 5% H2O on the NOx storage capacity of MgAlOx–rGO loaded with 2 wt% Pt and 10% K2CO3 (2Pt/10 K/MgAlOx–rGO) catalyst was also evaluated. In all, the 2Pt/10 K/MgAlOx–rGO catalyst not only exhibited high thermal stability and NOx storage capacity of 1.12 mmol · g‑1, but also possessed excellent H2O resistance and lean–rich cycling performance, with an overall 78.4% of NOx removal. This work provided a new scheme for the preparation of highly dispersed MgAlOx–rGO hybrid based NSR catalysts.

  1. Microstructure and electrical properties of MgAl[sub 2]O[sub 4] thin films for humidity sensing

    SciTech Connect

    Gusmano, G.; Montesperelli, G.; Traversa, E. . Dept. di Scienze e Tecnologie Chimiche); Mattogno, G. . Inst. di Teroria e Struttura Electronica)

    1993-03-01

    Active elements for humidity sensors based upon MgAl[sub 2]O[sub 4] thin films or sintered pellets were investigated. Thin films were deposited on Si/SiO[sub 2] substrates by radiofrequency (rf) sputtering. Sintered MgAl[sub 2]O[sub 4] pellets were prepared by traditional ceramic processing. Scanning electron microscopy (SEM) analysis showed that the thin films were rather dense and homogeneous, made up of clustered particles of about 20-30 nm, while the pellets showed a wide pore-size distribution. X-ray photoelectron spectroscopy (XPS) demonstrated that the thin films have a stoichiometry close to that of MgAl[sub 2]O[sub 4]. Sintered MgAl[sub 2]O[sub 4] is crystalline, while it is disordered in thin-film form. The presence of two different components of the Al 2p peaks was correlated with the structural difference between pellets and thin films. The relationship between good film-substrate adhesive properties and the chemical composition at the interface was studied. The electrical properties of the sensing elements were studied at 40C in environments at different relative humidity (RH) values between 2% and 95%, using ac impedance spectroscopy. MgAl[sub 2]O[sub 4] thin films showed interesting characteristics in terms of their use in humidity-measurement devices. Resistance versus RH sensitivity values showed variations as high as 4 orders of magnitude in the RH range tested for thin films, and 5 orders of magnitude for pellets. The differences in the electrical behavior of MgAl[sub 2]O[sub 4] pellets and thin films were correlated with their different microstructures.

  2. Calcium and Calcium-Base Alloys

    DTIC Science & Technology

    1949-01-01

    alloys have •been made in electrical contacts. Little is known of’ the high - calcium alloys,» The aluminum-calcium diagram from Hansen^1) is shown in...list is still incom- plete« No use has been suggested for high calcium -aluminum alloys, ..•Arsenic-pal’c-iüm- Alloys •K.. Calcium arsenide, OajAsg...hot CaCUy, by X-ray determination of the structure. The probability of finding a useful high - calcium alloy in this system is based-on-the-validity

  3. Intercalation and structural aspects of macroRAFT agents into MgAl layered double hydroxides

    PubMed Central

    Kostadinova, Dessislava; Cenacchi Pereira, Ana; Lansalot, Muriel; D’Agosto, Franck; Bourgeat-Lami, Elodie; Leroux, Fabrice; Taviot-Guého, Christine; Cadars, Sylvian

    2016-01-01

    Increasing attention has been devoted to the design of layered double hydroxide (LDH)-based hybrid materials. In this work, we demonstrate the intercalation by anion exchange process of poly(acrylic acid) (PAA) and three different hydrophilic random copolymers of acrylic acid (AA) and n-butyl acrylate (BA) with molar masses ranging from 2000 to 4200 g mol−1 synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization, into LDH containing magnesium(II) and aluminium(III) intralayer cations and nitrates as counterions (MgAl-NO3 LDH). At basic pH, the copolymer chains (macroRAFT agents) carry negative charges which allowed the establishment of electrostatic interactions with the LDH interlayer and their intercalation. The resulting hybrid macroRAFT/LDH materials displayed an expanded interlamellar domain compared to pristine MgAl-NO3 LDH from 1.36 nm to 2.33 nm. Depending on the nature of the units involved into the macroRAFT copolymer (only AA or AA and BA), the intercalation led to monolayer or bilayer arrangements within the interlayer space. The macroRAFT intercalation and the molecular structure of the hybrid phases were further characterized by Fourier transform infrared (FTIR) and solid-state 13C, 1H and 27Al nuclear magnetic resonance (NMR) spectroscopies to get a better description of the local structure. PMID:28144548

  4. Development of Lightweight Titanium Base Alloys

    DTIC Science & Technology

    1989-04-15

    program on Development of Lightweight Titanium Base Alloys was to develop new titanium alloys with 10% lower density, 50% higher elastic modulus, and...program. permitted the cvaluation of a low-dc-isity. dislicrsion-strengthcnicd 02 + y titanium aluminide , which has excellent high temperature strength...713e alloy has significantly higher strength than the titanium aluminides . The limited data for ’i-34AI-4Be show it to be very strong above 7(X)°C

  5. A Study of Magnesium-Base Metallic Systems and Development of Principles for Creation of Corrosion-Resistant Magnesium Alloys

    NASA Astrophysics Data System (ADS)

    Mukhina, I. Yu.

    2014-11-01

    The effect of 26 alloying elements on the corrosion resistance of high-purity magnesium in a 0.5-n solution of sodium chloride and in a humid atmosphere (0.005 n) is studied. The Mg - Li, Mg - Ag, Mg - Zn, Mg - Cu, Mg - Gd, Mg - Al, Mg - Zr, Mg - Mn and other binary systems, which present interest as a base for commercial or perspective castable magnesium alloys, are studied. The characteristics of corrosion resistance of the binary alloys are analyzed in accordance with the group and period of the Mendeleev's periodic law. The roles of the electrochemical and volume factors and of the factor of the valence of the dissolved element are determined.

  6. Enhanced high temperature performance of MgAl2O4-supported Pt-BaO lean NOx trap catalysts

    SciTech Connect

    Kwak, Ja Hun; Kim, Do Heui; Szanyi, Janos; Cho, Sung June; Peden, Charles HF

    2012-03-05

    The structural and chemical characteristics of Pt/BaO lean-NO{sub x} trap (LNT) catalysts supported on {gamma}-Al{sub 2}O{sub 3} and MgAl{sub 2}O{sub 4} are compared in this study. The Pt-BaO/MgAl{sub 2}O{sub 4} sample shows relatively low NO{sub x} uptake at temperatures below 300 C, and the temperature of maximum NO{sub x} uptake (T{sub max}) is shifted to 350 C in comparison to that of Pt-BaO/Al{sub 2}O{sub 3} (T{sub max} {approx}250 C). More importantly, the NO{sub x} uptake over the MgAl{sub 2}O{sub 4}-supported catalyst at 350 C is twice that of the alumina-based one. The shift toward the higher temperature NO{sub x} uptake is explained by the larger interfacial area between Pt and BaO, due to smaller Pt clusters as evidenced by TEM and Pt L3 EXAFS. In situ TR-XRD results demonstrate that the formation of a BaAl{sub 2}O{sub 4} phase in the BaO/MgAl{sub 2}O{sub 4} LNT catalyst occurs at a temperature about 100 C higher than on BaO/Al{sub 2}O{sub 3}, which may also represent a beneficial attribute of the BaO/MgAl{sub 2}O{sub 4} LNT with respect to catalyst stability.

  7. Magnesium-based biodegradable alloys: Degradation, application, and alloying elements

    PubMed Central

    Pogorielov, Maksym; Husak, Eugenia; Solodivnik, Alexandr; Zhdanov, Sergii

    2017-01-01

    In recent years, the paradigm about the metal with improved corrosion resistance for application in surgery and orthopedy was broken. The new class of biodegradable metal emerges as an alternative for biomedical implants. These metals corrode gradually with an appropriate host response and release of corrosion products. And it is absolutely necessary to use essential metals metabolized by hosting organism with local and general nontoxic effect. Magnesium serves this aim best; it plays the essential role in body metabolism and should be completely excreted within a few days after degradation. This review summarizes data from Mg discovery and its first experimental and clinical application of modern concept of Mg alloy development. We focused on biodegradable metal application in general surgery and orthopedic practice and showed the advantages and disadvantages Mg alloys offer. We focused on methods of in vitro and in vivo investigation of degradable Mg alloys and correlation between these methods. Based on the observed data, a better way for new alloy pre-clinical investigation is suggested. This review analyzes possible alloying elements that improve corrosion rate, mechanical properties, and gives the appropriate host response. PMID:28932493

  8. Magnesium-based biodegradable alloys: Degradation, application, and alloying elements.

    PubMed

    Pogorielov, Maksym; Husak, Eugenia; Solodivnik, Alexandr; Zhdanov, Sergii

    2017-03-01

    In recent years, the paradigm about the metal with improved corrosion resistance for application in surgery and orthopedy was broken. The new class of biodegradable metal emerges as an alternative for biomedical implants. These metals corrode gradually with an appropriate host response and release of corrosion products. And it is absolutely necessary to use essential metals metabolized by hosting organism with local and general nontoxic effect. Magnesium serves this aim best; it plays the essential role in body metabolism and should be completely excreted within a few days after degradation. This review summarizes data from Mg discovery and its first experimental and clinical application of modern concept of Mg alloy development. We focused on biodegradable metal application in general surgery and orthopedic practice and showed the advantages and disadvantages Mg alloys offer. We focused on methods of in vitro and in vivo investigation of degradable Mg alloys and correlation between these methods. Based on the observed data, a better way for new alloy pre-clinical investigation is suggested. This review analyzes possible alloying elements that improve corrosion rate, mechanical properties, and gives the appropriate host response.

  9. Mg/Al double-metal hydroxide regeneration of anion exchange resin by electric field intensification.

    PubMed

    Wang, Ying; Li, Zhun; Li, Yansheng; Liu, Zhigang

    2017-03-01

    Fouled anion exchange resins were regenerated by electric field intensification of Mg/Al double-metal hydroxides. Regenerative experiments were performed with varying voltages (10-30 V) and dosages of Mg/Al hydroxides (0.045-0.135 mol and 0.015-0.045 mol, respectively) for 1-5 h. Optimal results were obtained under the following regenerative conditions: 20 V, 4 h, and 0.09/0.03 mol of Mg/Al hydroxides. The maximum regenerative capacity of resins was increased to 41.07%. The regenerative mechanism was presented by Fourier-transform infrared spectrum of resins and Mg/Al hydroxides, and the regenerative degree was analyzed with respect to conductivity, pH value, and electric current. Mg/Al hydroxides were also recycled after the regeneration. This method was proven to be cost-effective and environmentally friendly.

  10. Simultaneous removal of Cl- and SO4 2- from seawater using Mg-Al oxide: kinetics and equilibrium studies

    NASA Astrophysics Data System (ADS)

    Kameda, Tomohito; Oba, Jumpei; Yoshioka, Toshiaki

    2017-03-01

    Mg-Al oxide, obtained by the thermal decomposition of a CO3 2--intercalated Mg-Al layered double hydroxide (CO3·Mg-Al LDH), simultaneously absorbed Cl- and SO4 2- from seawater and generated a Mg-Al LDH intercalated with Cl- and SO4 2-. The Mg-Al oxide with a molar ratio Mg/Al = 4 was more superior than the oxide with Mg/Al = 2 for Cl- removal, whereas a reverse phenomenon was observed for SO4 2- removal. The removal of Cl- and SO4 2- by the Mg-Al oxide with Mg/Al = 4 could be represented by first-order and pseudo second-order reactions, respectively. The removal of both Cl- and SO4 2- by the Mg-Al oxide with Mg/Al = 2 could be represented by a pseudo second-order reaction. The removal of both Cl- and SO4 2- by the Mg-Al oxides with Mg/Al = 4 and 2 was proceeded under chemical reaction control. The adsorption isotherms for Cl- and SO4 2- adsorbed by the Mg-Al oxides could be expressed by Langmuir-type adsorption. These reactions were derived from monolayer adsorption, indicating the intercalation of Cl- and SO4 2- in the interlayer space of Mg-Al LDH. The uptake of Cl- and SO4 2- from seawater by Mg-Al oxide was proceeded spontaneously.

  11. Iron-based amorphous alloys and methods of synthesizing iron-based amorphous alloys

    DOEpatents

    Saw, Cheng Kiong; Bauer, William A.; Choi, Jor-Shan; Day, Dan; Farmer, Joseph C.

    2016-05-03

    A method according to one embodiment includes combining an amorphous iron-based alloy and at least one metal selected from a group consisting of molybdenum, chromium, tungsten, boron, gadolinium, nickel phosphorous, yttrium, and alloys thereof to form a mixture, wherein the at least one metal is present in the mixture from about 5 atomic percent (at %) to about 55 at %; and ball milling the mixture at least until an amorphous alloy of the iron-based alloy and the at least one metal is formed. Several amorphous iron-based metal alloys are also presented, including corrosion-resistant amorphous iron-based metal alloys and radiation-shielding amorphous iron-based metal alloys.

  12. TL and OSL studies of carbon doped magnesium aluminate (MgAl2O4:C)

    NASA Astrophysics Data System (ADS)

    Raj, Sanu S.; Mishra, D. R.; Soni, Anuj; Grover, V.; Polymeris, G. S.; Muthe, K. P.; Jha, S. K.; Tyagi, A. K.

    2016-10-01

    The MgAl2O4:C has been synthesized by using two different methods by electron gun and vacuum assisted melting of MgAl2O4 in presence of graphite. The MgAl2O4:C phosphor thus developed by these two different methods have similar types of the TL/OSL defects with multiple overlapping TL glow peaks from 100 °C to 400 °C. The Computerized Curve De-convolution Analysis (CCDA) has been used to measure TL parameters such as thermal trap depth, frequency factor and order of kinetic associated with charge transfer process in TL phenomenon. The investigated TL/OSL results show that these two methods of incorporating carbon in MgAl2O4 have generated closely resemble the defects of similar types in MgAl2O4:C lattice. However, the MgAl2O4:C synthesized by electron gun shows relatively larger concentration of the TL/OSL defects as compared to MgAl2O4:C synthesized using vacuum assisted melting method. The photo-ionization cross-section (PIC) associated with fastest OSL component of MgAl2O4: C is found to be ∼ 0.5 times than that of fastest OSL component of commercially available dosimetric grade α-Al2O3:C. The MgAl2O4:C thus developed shows good dynamic OSL dose linearity from few mGy to 1 Gy. This work reveals that MgAl2O4:C could be developed as potential tissue equivalent OSL / TL material.

  13. 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.

  14. P- T- X controls on Ca and Na distribution between Mg-Al tourmaline and fluid

    NASA Astrophysics Data System (ADS)

    Berryman, Eleanor J.; Wunder, Bernd; Rhede, Dieter; Schettler, Georg; Franz, Gerhard; Heinrich, Wilhelm

    2016-04-01

    Ca-Na partitioning between tourmaline and a coexisting fluid is investigated in the system CaO-Na2O-B2O3-Al2O3-MgO-SiO2-H2O-Cl between 0.2-4.0 GPa and 500-700 °C. The synthesis experiments produced a mineral assemblage of tourmaline, coesite/quartz, and in some cases additional phases, typically comprising <1 wt% of the solid product. The synthesized tourmalines are solid solutions of dravite [NaMg3Al6Si6O18(BO3)3(OH)3(OH)], "oxy-uvite" (i.e. "Ca-Mg-O root name") [CaMg3Al6Si6O18(BO3)3(OH)3O], and magnesio-foitite [☐(Mg2Al)Al6Si6O18(BO3)3(OH)3(OH)]. Starting materials comprised a fluid of constant ionic strength (2.00 m) and an oxide mixture with a constant Mg/Al ratio. As a result, the number of vacancies at the X site and the Mg/Al ratio of tourmaline crystals synthesized at the same temperature vary only slightly. The major solid solution is Ca-Na exchange at the X site via the exchange vector X Ca W O[ X Na W (OH)]-1, with the exchange vector X (Ca☐)[ X Na2]-1 serving as a secondary Ca-incorporation mechanism. Tourmaline's X-site composition reflects the fluid composition, whereby the Ca (or Na) concentration in the fluid corresponds with the Ca (or Na) content in tourmaline at each pressure and temperature. At 0.2 GPa, 700 °C, Ca preferentially partitions into tourmaline, producing the most Ca-rich tourmaline crystals synthesized here. At pressures >1.0 GPa, Ca partitions preferentially into the fluid, resulting in Na-dominant tourmaline compositions. Temperature has a secondary effect on Ca-Na partitioning, with higher temperatures correlating with increased Ca incorporation in tourmaline. Based on the experimental findings, tourmaline is expected to have Ca-rich compositions when it forms in low pressure, high-temperature Ca-rich rocks, consistent with the current record of tourmaline occurrence. The bulk Mg/Al ratio and the pH of the tourmaline-forming system may also affect Ca incorporation in tourmaline, but remain to be investigated experimentally.

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

    NASA Astrophysics Data System (ADS)

    Schonfeld, E.

    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.

  16. 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.

  17. Synthesis and adsorption properties of hierarchical Fe3O4@MgAl-LDH magnetic microspheres

    NASA Astrophysics Data System (ADS)

    Wu, Xiaoge; Li, Bo; Wen, Xiaogang

    2017-04-01

    In this study, Fe3O4 microspheres were prepared by a hydrothermal method, and then the synthesized Fe3O4 microspheres were used as template to prepare Fe3O4@MgAl-LDH composite microspheres by a coprecipitation process. Morphology, composition, and crystal structure of synthesized nanomaterials were characterized by X-ray powder diffractometry, scanning electron microscopy, and Fourier transform infrared spectroscopy technologies. The composite hierarchical microspheres are composed of inner Fe3O4 core and outer MgAl-LDH-nanoflake layer, and the average thickness of MgAl-LDH-nanoflake is about 70 nm. The adsorption property of the products toward congo red was also measured using UV-vis spectrometer. The result demonstrated that the Fe3O4@MgAl-LDH composite adsorbent could remove 99.8% congo red in 30 min, and the maximum adsorption capacity is about 404.6 mg/g, while congo red removal rate of pure MgAl-LDH and Fe3O4 are only 86.3 and 53.1% in 40 min, respectively, and their adsorption capacity are 345.72 and 220.56 mg/g, respectively. It indicates the composite Fe3O4@ MgAl-LDH nanomaterials have better adsorption performance than pure Fe3O4 and MgAl-LDH nanomaterials. In addition, the magnetic nanocomposites could be separated easily, and it demonstrated good cycle performance.

  18. [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.

  19. Indentation Size Effect (ISE) of Transparent AION and MgAl2O4

    DTIC Science & Technology

    2006-07-01

    Indentation Size Effect (ISE) of Transparent AlON and MgAl2O4 by Parimal J. Patel, Jeffrey J. Swab, Mark Staley, and George D. Quinn ARL...3852 July 2006 Indentation Size Effect (ISE) of Transparent AlON and MgAl2O4 Parimal J. Patel and Jeffrey J. Swab Weapons and Materials...CONTRACT NUMBER 5b. GRANT NUMBER 4. TITLE AND SUBTITLE Indentation Size Effect (ISE) of Transparent AlON and MgAl2O4 5c. PROGRAM ELEMENT NUMBER 5d

  20. Hot Corrosion of Cobalt-Base Alloys

    DTIC Science & Technology

    1975-06-01

    Cast Alloys : NASA VIA, B-1900, 713C and 738X", Report NASA TN D-7682, Lewis Research Center, Cleveland, Ohio, August 1974. 36. Giggins, C.S. and...resistance of cobalt-base and nickel-base alloys . The contract was accomplished under the technical direction of Dr. H. C. Graham of the Aerospace Research...Interpretation of Results 3. SODIUM SULFATE INDUCED HOT CORROSION OF Co-25Al AND Co-35Cr ALLOYS a. Introduction b. Experimental Co-25Al c. Experimental

  1. Noncontact atomic force microscopy study of the spinel MgAl(2)O(4)(111) surface.

    PubMed

    Rasmussen, Morten K; Meinander, Kristoffer; Besenbacher, Flemming; Lauritsen, Jeppe V

    2012-01-01

    Based on high-resolution noncontact atomic force microscopy (NC-AFM) experiments we reveal a detailed structural model of the polar (111) surface of the insulating ternary metal oxide, MgAl(2)O(4) (spinel). NC-AFM images reveal a 6√3×6√3R30° superstructure on the surface consisting of patches with the original oxygen-terminated MgAl(2)O(4)(111) surface interrupted by oxygen-deficient areas. These observations are in accordance with previous theoretical studies, which predict that the polarity of the surface can be compensated by removal of a certain fraction of oxygen atoms. However, instead of isolated O vacancies, it is observed that O is removed in a distinct pattern of line vacancies reflected by the underlying lattice structure. Consequently, by the creation of triangular patches in a 6√3×6√3R30° superstructure, the polar-stabilization requirements are met.

  2. 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

  3. 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).

  4. 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.

  5. Bias voltage effects on tunneling magnetoresistance in Fe/MgAl2O4/Fe (001 ) junctions: Comparative study with Fe/MgO/Fe(001) junctions

    NASA Astrophysics Data System (ADS)

    Masuda, Keisuke; Miura, Yoshio

    2017-08-01

    We investigate bias voltage effects on the spin-dependent transport properties of Fe/MgAl 2O 4 /Fe(001) magnetic tunneling junctions (MTJs) by comparing them with those of Fe/MgO/Fe(001) MTJs. By means of the nonequilibrium Green's function method and the density functional theory, we calculate bias voltage dependencies of magnetoresistance (MR) ratios in both the MTJs. We find that in both the MTJs, the MR ratio decreases as the bias voltage increases and finally vanishes at a critical bias voltage Vc. We also find that the critical bias voltage Vc of the MgAl 2O 4 -based MTJ is clearly larger than that of the MgO-based MTJ. Since the in-plane lattice constant of the Fe/MgAl 2O 4 /Fe(001) supercell is twice that of the Fe/MgO/Fe(001) one, the Fe electrodes in the MgAl 2O 4 -based MTJs have an identical band structure to that obtained by folding the Fe band structure of the MgO-based MTJs in the Brillouin zone of the in-plane wave vector. We show that such a difference in the Fe band structure is the origin of the difference in the critical bias voltage Vc between the MgAl 2O 4 - and MgO-based MTJs.

  6. Corrosion of nickel-base alloys

    SciTech Connect

    Scarberry, R.C.

    1985-01-01

    The volume consists of three tutorial lectures and 18 contributed papers. The three tutorial lectures provide state-of-the-art background on the physical metallurgy of nickel-base alloys as it relates to corrosion. Also featured are the mechanisms and applications of these alloys and an insight into the corrosion testing techniques. The three tutorial lecture papers will help acquaint newcomers to this family of alloys with a thorough overview. The contributed papers are categorized into four major topics: general corrosion, stress corrosion cracking, fatigue and localized corrosion. Each topic is key-noted by one invited lecture followed by several contributed papers. The papers in the general corrosion section are wide ranging and cover the aspects of material selection, development of galvanic series in corrosive environments, corrosion resistance characteristics, hydrogen permeation and hydrogen embrittlement of nickel and some nickel-base alloys.

  7. Transient oxidation of multiphase Ni-Cr base alloys

    SciTech Connect

    Baran, G.; Meraner, M.; Farrell, P.

    1988-06-01

    Four commercially available Ni-Cr-based alloys used with porcelain enamels were studied. Major alloying elements were Al, Be, Si, B, Nb, and Mo. All alloys were multiphase. During heat treatments simulating enameling conditions, phase changes occurred in most alloys and were detected using hardness testing, differential thermal analysis (DTA), and microscopy. Oxidation of these alloys at 1000/degrees/C for 10 min produced an oxide layer consisting principally of chromium oxide, but the oxide morphology varied with each alloy depending on the alloy microstructure. Controlling alloy microstructure while keeping the overall composition unchanged may be a means of preventing wrinkled poorly adherent scales from forming.

  8. Role of Grain Boundaries in the Mechanism of Plasma Hydrogenation of Nanocrystalline MgAl Films

    SciTech Connect

    Milcius, Darius; Pranevicius, Liudas; Templier, Claude; Bobrovaite, Birute; Barnackas, Irmantas

    2006-05-24

    Nanocrystalline aluminum hydrides (alanates) are potential hydrogen storage materials for PEM fuel cell applications. One of candidates is magnesium alanate, Mg(AlH4)2, which contains 9.3 wt. % of hydrogen. In the present work, the effects of Ti catalyst in improving the kinetics of hydrogen uptake and release are investigated. The 2-5 {mu}m thick MgAl films have been hydrogenated employing plasma immersion ion implantation technique as a function of Ti-content. Nanocrystalline MgAl films were prepared by magnetron sputter deposition in vacuum. Titanium atoms were incorporated simultaneously into the growing film. Morphological and structural properties were studied by scanning electron and atomic force microcopies and X-ray diffraction technique. It is shown that the microstructure of the hydrided/dehydrided MgAl film is highly defected and demonstrates dispersed/amorphous cluster-like structure. Ti atoms in MgAl film kinetically enhance the dehydrogenation of magnesium alanate film. For Ti-doped MgAl film the dehydrogenation process becomes about 1.5 times shorter and the dehydrogenation temperature about 50 K less than for Ti-undoped film for the temperature rise rate equal to 18 K-min-1. It is shown when hydrogenated MgAl film is exposed to air a compact amorphous Al2O3 layer with typically 3-5 nm thickness grows on the surface. Thin native oxide acts as a permeation barrier for hydrogen. It has been found that the major part of hydrogen effuses at {approx}630 K and the effusion process is controlled by the migration of hydrogen through the surface oxide layer.

  9. Friction behavior of Mg-Al-CO3 layered double hydroxide prepared by magnesite

    NASA Astrophysics Data System (ADS)

    Wang, Xiaobo; Bai, Zhimin; Zhao, Dong; Zhao, Fuyan

    2013-07-01

    In this paper, Mg-Al-CO3 LDH was prepared by magnesite under chemical precipitation and hydrothermal methods. In order to improve the dispersion of LDH in base oil, the as-prepared sample was modified with sodium laurate. The obtained material (GMAC-LDH) was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry and thermo gravimetric analyzer (DSC-TGA) and scanning electron microscope (SEM). The results show that the modified LDH has platelet morphology with a near hexagon shape. In addition, the tribological properties of GMAC-LDH were evaluated by four-ball friction tester and gear tester. As a lubricant, GMAC-LDH possesses an excellent property on reducing friction and wear of friction pair. The results of friction tests indicated that the friction coefficient, diameter of wear scar and power consumption of the oil with GMAC-LDH was reduced by 11.0%, 8.5% and 2.1% as compared with that of base oil.

  10. Simultaneous removal of SO2 and NO2 using a Mg-Al oxide slurry treatment.

    PubMed

    Kameda, Tomohito; Kodama, Aki; Yoshioka, Toshiaki

    2013-11-01

    SO2 and NO2 were simultaneously removed from a mixed gas using a Mg-Al oxide slurry treatment. Both adsorption to the oxide material itself and dissolution of the gases in the aqueous slurry contributed to the removal. A comparison was made between removal of the two gases separately and the simultaneous process. The removal of SO2 using both the simultaneous and individual process was similar; however, the removal of NO2 was lower for the simultaneous process. For the individual treatments, SO2 and NO2 were separately dissolved in the Mg-Al oxide slurry to produce SO3(2-), NO2(-), and NO3(-), which were subsequently removed by the Mg-Al oxide. However, when the simultaneous process was employed, the dissolved gases were seen to have a significant effect on each other. It was speculated that the production of NO2(-) was increased by the reduction of NO2 by SO3(2-). On increasing the quantity of the Mg-Al oxide, or on raising the temperature of the system, the removal of SO2 increased, with a concurrent decrease in NO2 removal. The increase in removal of SO3(2-) was speculated to hinder the conversion of NO2 to NO2(-), therefore decreasing the removal of the nitrogen species. The results demonstrate that the Mg-Al oxide slurry was highly effective for simultaneously removing NO2 and SO2 from a mixed gas.

  11. Structural Characterization of Mg/Al hydrotalcite-like Compounds and their Thermal Stability

    NASA Astrophysics Data System (ADS)

    Zhang, Shuhua; Yang, Siyuan; Wang, Cheng; Liu, Weijun; Gu, Xiaodan; Gan, Wenjun; Xue, Xiaoyu

    2014-03-01

    Hydrotalcite-like compounds, repersented by the formula [M1-x 2 + Mx3+ (OH)2]Xx/n n - . nH2O (M2+ = Ni2+, Mg2+, Cu2+,etc; M3+ = Al3+, Fe3+, etc; Xn- = CO32- , NO3-,etc) possess the brucite-like layers [Mg(OH)2] with positive charge and anionic compounds in the interlayer to form neutral materials. Catalytic effects to decompose NOx from automobile exhaust were highly related with the difference of M2+ and thermal stability because the catylists locate are about 200 ~ 500°. In this paper, Mg-Al-Cu and Mg-Al-Ni hydrotalcite-like compounds were characterized by XRD and FT-IR spectra and the thermal stability were analyzed by TGA and DTA. Even though they both have the typical diffraction peaks of hydrotalcites, but their interlayer spaces are different. Some weak chemical bonds were observed to be formed in Mg-Al-Ni hydrotalcites by FT-IR. Mg-Al-Ni hydrotalcite-like compound degraded at lower temperature, by contrast, Mg-Al-Cu hydrotalcite has the better structural stablilty and thermal stability.

  12. Nickel-base alloys for severe environments

    SciTech Connect

    Wilson, R.K.; Flower, H.L.; Hack, G.A.J.; Isobe, S.

    1996-03-01

    Inconel alloys MA754 and MA758 are nickel-base, oxide dispersion-strengthened superalloys made by mechanical alloying. The simple nickel-chromium matrix, when combined with the strengthening effect of the yttrium oxide dispersoid during mechanical alloys, provides excellent creep properties, resistance to thermal fatigue, and surface stability suitable for operation without protective coatings. Gas turbine engine components are primary applications for alloy MA754, but this aerospace alloy has been applied in many other products that operate in severe conditions, and alloy MA758 was developed specifically for aggressive, elevated temperature industrial environments. Billets for large bar and plate are typically consolidated by hot isostatic pressing (HIP), because this technology allows production of forms suitable for a variety of industrial components. Material consolidated by HIP and conventionally worked by extrusion and hot rolling generally exhibits properties that are more isotropic than those of material consolidated by extrusion. However, the degree of anisotropy depends strongly on the specific processing of the consolidated billet. This article describes production of new mill shapes from HIP billets, and reviews current and potential applications such as skid rails for high-temperature walking-beam furnaces, heat treating furnace parts, equipment for handling molten glass, and furnace tubes.

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

    SciTech Connect

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

    2011-01-01

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

  14. An electrochemical investigation of mechanical alloying of MgNi-based hydrogen storage alloys

    NASA Astrophysics Data System (ADS)

    Jiang, Jian-Jun; Gasik, Michael

    The electrochemical properties of amorphous MgNi-based hydrogen storage alloys synthesized by mechanical alloying (MA) were evaluated. The results show that these amorphous Mg 50Ni 50 alloys exhibit a higher discharge capacity and relatively good rate capacity at a suitable grinding time while their cycle life is very poor. In order to improve the cycle life, the surface of the amorphous Mg 50Ni 50 alloy was coated with Ti, Al and Zr in Spex 8000 mill/mixer and the coating effects were further investigated. Based on experimental results, two kinds of MgNi-based amorphous alloys are designed by substituting part of Mg in MgNi-based alloys by suitable elements. These alloys are then composed of four components. Thus, the cycle life of electrodes consisting of these quaternary amorphous alloys is greatly improved.

  15. Removal of perchlorate in water by calcined MgAl-CO3 layered double hydroxides.

    PubMed

    Yang, Yiqiong; Gao, Naiyun; Deng, Yang; Yu, Guoping

    2013-04-01

    Perchlorate is widely known as an inorganic endocrine disruptor. In this study, MgAl-CO3 layered double hydroxides with different Mg/Al molar ratios were prepared using a coprecipitation method and followed by a calcination process at a temperature range of 300 to 700 degrees C. Results showed that the best synthesis conditions were a calcination temperature of 550 degrees C and Mg/Al molar ratio of 3. Further, the adsorbent and its adsorption product were characterized by x-ray diffraction, Fourier transform-infrared spectroscopy, and thermogravimetric-differential thermal analysis. The layered double hydroxides structures in the adsorbent were lost during calcination at 550 degrees C but were reconstructed subsequent to adsorption of perchlorate, indicating that the "memory effect" appeared to play an important role in perchlorate adsorption. The perchlorate adsorption pattern was best described by the pseudo-second-order kinetics model, while the Freundlich isotherms appropriately explained perchlorate adsorption data.

  16. Thermal Behavior of Phosphate Intercalated Mg/Al-LAYERED Double Hydroxides

    NASA Astrophysics Data System (ADS)

    Shimamura, Akihiro; Kurashina, Masashi; Kanezaki, Eiji

    The thermal behavior of Mg and Al layered double hydroxide with interlayer hydrogen phosphate (abb. as Mg/Al-HPO4-LDH) is investigated below 1273 K by means of XRD, TG-DTA, SEM and FT-IR. The basal spacing of Mg/Al-HPO4-LDH decreases with increasing heating temperature stepwise in two stages; from 1.07 nm at 293 K to 0.85 nm at 333 K in the first stage and to 0.73 nm between 373 K and 443 K in the second one. The LDH becomes amorphous above 443 K until Mg3 (PO4)2, MgO and MgAl2O4 (spinel) appear at 1273 K. SEM images of the LDH show plate-like crystallites both before and after heating at 473 K.

  17. 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.

  18. Chemical stability and Ce doping of LiMgAlF6 neutron scintillator

    DOE PAGES

    Du, M. H.

    2014-11-13

    We perform density functional calculations to investigate LiMgAlF6 as a potential neutron scintillator material. The calculations of enthalpy of formation and phase diagram show that single-phase LiMgAlF6 can be grown but it should be more difficult than growing LiCaAlF6 and LiSrAlF6. Moreover, the formation energy calculations for substitutional Ce show that the concentration of Ce on the Al site is negligible but a high concentration (>1 at.%) of Ce on the Mg site is attainable provided that the Fermi level is more than 5 eV lower than the conduction band minimum. Acceptor doping should promote Ce incorporation in LiMgAlF6.

  19. Sonochemical preparation of high surface area MgAl2O4 spinel.

    PubMed

    Troia, A; Pavese, M; Geobaldo, F

    2009-01-01

    High surface area MgAl(2)O(4) has been synthesised by a sonochemical method. Two kinds of precursors were used, alkoxides and nitrates/acetates and in both cases nanostructured MgAl(2)O(4) was obtained. The effect of the addition of a surfactant during the sonication, cetyl trimethyl ammonium bromide, was also investigated. In the case of alkoxides precursors the as-made product is a mixture of hydroxides of aluminium and magnesium, while with nitrates/acetates a gel is obtained after sonication, containing the metal hydroxides and ammonium nitrate. Heating at 500 degrees C transforms the as-made products into MgAl(2)O(4) spinel phase. The surface area is up to 267 m(2)/g after treatment at 500 degrees C and 138 m(2)/g at 800 degrees C.

  20. 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.

  1. Occurrence of wagnerite in Mg-Al granulites of Sonapahar, Meghalaya

    NASA Astrophysics Data System (ADS)

    Dwivedi, S. B.; Theunuo, K.

    2017-06-01

    We report for the first time the occurrence of rare phosphate wagnerite as a stable phase from the Mg-Al granulites of Sonapahar. The wagnerite bearing assemblages consist of the spinel, phlogopite, brucite and corundum. The wagnerite appears in the Mg-Al granulites due to the break-down of spinel and fluorapatite. The mineral chemistry of the phases has been discussed from the EPMA data, which reveals that the fluorine content of the wagnerite is relatively low due to the exchange of F to coexisting phases. The major oxide analysis of the rocks show the low content of Ca, which is the requisite for the occurrences of wagnerite.

  2. Cetyltrimethyl ammonium bromide-Mg/Al hydrotalcite for removal phenol in water

    NASA Astrophysics Data System (ADS)

    Kurniawati, Puji; Wiyantoko, Bayu; Purbaningtias, Tri Esti; Muzdalifah

    2017-03-01

    Hydrotalcite materials was synthesized by using Cetyltrimethyl Ammonium Bromide (CTAB) and Mg/Al layered double hydroxide with ratio molar 3:1. Synthesis of CTAB-Mg/Al hydrotalcite was carried out using ex situ co-precipitation method at pH 10±0.5. Removal of phenol was optimum at medium pH 6 and it had optimum contact time in 300 min. It followed pseudo second order with adsorption rate constant was 1.15.10-4 mM-1.min-1. The maximum adsorption capacities obtained from the Langmuir model was 35.71 mg.g-1 at room temperature.

  3. Mass spectrometric study of the evaporation of MgAl2O4 spinel

    NASA Astrophysics Data System (ADS)

    Shornikov, S. I.

    2017-01-01

    The evaporation of MgAl2O4 spinel is studied via high-temperature Knudsen effusion mass spectrometry in the temperature range of 1850-2250 K. In the gas phase, molecular components typical of the simple oxides in the spinel and traces of gaseous complex oxide MgAlO are identified above the samples. The resulting values of the partial vapor pressures of the molecular components contained in the gas phase over the spinel are compared with those corresponding to simple oxides for the first time.

  4. Defects on the Surface of Ti-Doped MgAl2O4 Nanophosphor.

    PubMed

    Lim, Jaehyuk; Kim, Yongseon; Kim, Sungdae; Kim, Youngwoon; Kang, Shinhoo

    2017-09-19

    Ti-doped nano MgAl2O4 for white emission was synthesized by combustion method. Extrinsic Schottky defects, Al vacancies and Ti(4+) dopant in Al sites, which are considered to be responsible for bluish-white emission, were observed by STEM on the surface of Ti-doped nano MgAl2O4 powder. The stabilities of the Schottky defect associates, (TiAl(·)-VAl''')'', were demonstrated by DFT calculation. The emission behavior was interpreted with these results.

  5. Testing LaMgAl11O19 crystal for X-ray spectroscopy

    SciTech Connect

    Chen, H; Beiersdorfer, P; Baronova, E; Kalashnikova, I; Stepanenko, M

    2004-03-31

    We investigated the properties of the rare earth crystal LaMgAl{sub 11}O{sub 19} and its application to soft X-ray spectroscopy. Its relative reflectivity and half width rocking curve were measured to up to the reflection order of 28. In addition, a comparative measurement of the iron L-shell soft X-ray line emission was made on the EBIT-I Livermore electron beam ion trap by fielding the LaMgAl{sub 11}O{sub 19} crystal side by side with a rubidium hydrogen phthalate crystal in a flat crystal spectrometer. From these measurements, reflectivity and spectral resolving power were determined.

  6. Welding and brazing of nickel and nickel-base alloys

    NASA Technical Reports Server (NTRS)

    Mortland, J. E.; Evans, R. M.; Monroe, R. E.

    1972-01-01

    The joining of four types of nickel-base materials is described: (1) high-nickel, nonheat-treatable alloys, (2) solid-solution-hardening nickel-base alloys, (3) precipitation-hardening nickel-base alloys, and (4) dispersion-hardening nickel-base alloys. The high-nickel and solid-solution-hardening alloys are widely used in chemical containers and piping. These materials have excellent resistance to corrosion and oxidation, and retain useful strength at elevated temperatures. The precipitation-hardening alloys have good properties at elevated temperature. They are important in many aerospace applications. Dispersion-hardening nickel also is used for elevated-temperature service.

  7. Rapid solidification of Nb-base alloys

    NASA Technical Reports Server (NTRS)

    Gokhale, A. B.; Javed, K. R.; Abbaschian, G. J.; Lewis, R. E.

    1988-01-01

    New Nb-base alloys are of interest for aerospace structural applications at high temperatures, viz, 800 to 1650 C. Fundamental information regarding the effects of rapid solidification in achieving greatly refined microstructures, extended solid solubility, suppression of embrittling equilibrium phases, and formation of new phases is desired in a number of Nb-X alloys. The microstructures and selected properties of Nb-Si and other Nb-base alloys are presented for materials both rapidly quenched from the equilibrium liquidus and rapidly solidified following deep supercooling. Electromagnetic levitation was used to achieve melting and supercooling in a containerless inert gas environment. A variety of solidification conditions were employed including splatting or drop casting of supercooled samples. The morphology and composition of phases formed are discussed in terms of both solidification history and bulk composition.

  8. Irradiation creep of vanadium-base alloys

    SciTech Connect

    Tsai, H.; Billone, M.C.; Strain, R.V.; Smith, D.L.; Matsui, H.

    1998-03-01

    A study of irradiation creep in vanadium-base alloys is underway with experiments in the Advanced Test Reactor (ATR) and the High Flux Isotope Reactor (HFIR) in the United States. Test specimens are thin-wall sealed tubes with internal pressure loading. The results from the initial ATR irradiation at low temperature (200--300 C) to a neutron damage level of 4.7 dpa show creep rates ranging from {approx}0 to 1.2 {times} 10{sup {minus}5}/dpa/MPa for a 500-kg heat of V-4Cr-4Ti alloy. These rates were generally lower than reported from a previous experiment in BR-10. Because both the attained neutron damage levels and the creep strains were low in the present study, however, these creep rates should be regarded as only preliminary. Substantially more testing is required before a data base on irradiation creep of vanadium alloys can be developed and used with confidence.

  9. Oxygen diffusion in vanadium-based alloys

    SciTech Connect

    de Avillez, R.R.

    1981-01-01

    The experimental study of transport and equilibrium properties of oxygen in vanadium-based alloys was made by EMF measurements on solid electrolytic cells over the temperature range of 873 to 1423/sup 0/K. The oxygen diffusion in vanadium was not significantly modified by small additions of Ti, Cr, Ni, Nb and Ta. The increase in the activation energy for oxygen diffusion in the V-based alloys containing Cr, Ni, Nb and Ta probably reflects the effect of these substitutional solutes on the activity coefficient of oxygen. The oxygen activity was increased by the addition of 1 at % of Cr, Ni and Nb, and decreased by the addition of Ti and Ta. However, the effects in the alloys containing Nb and Ta are very small.

  10. 21 CFR 872.3710 - Base metal alloy.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Base metal alloy. 872.3710 Section 872.3710 Food... DEVICES DENTAL DEVICES Prosthetic Devices § 872.3710 Base metal alloy. (a) Identification. A base metal alloy is a device composed primarily of base metals, such as nickel, chromium, or cobalt, that...

  11. 21 CFR 872.3710 - Base metal alloy.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Base metal alloy. 872.3710 Section 872.3710 Food... DEVICES DENTAL DEVICES Prosthetic Devices § 872.3710 Base metal alloy. (a) Identification. A base metal alloy is a device composed primarily of base metals, such as nickel, chromium, or cobalt, that...

  12. 21 CFR 872.3710 - Base metal alloy.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Base metal alloy. 872.3710 Section 872.3710 Food... DEVICES DENTAL DEVICES Prosthetic Devices § 872.3710 Base metal alloy. (a) Identification. A base metal alloy is a device composed primarily of base metals, such as nickel, chromium, or cobalt, that...

  13. 21 CFR 872.3710 - Base metal alloy.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Base metal alloy. 872.3710 Section 872.3710 Food... DEVICES DENTAL DEVICES Prosthetic Devices § 872.3710 Base metal alloy. (a) Identification. A base metal alloy is a device composed primarily of base metals, such as nickel, chromium, or cobalt, that...

  14. 21 CFR 872.3710 - Base metal alloy.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Base metal alloy. 872.3710 Section 872.3710 Food... DEVICES DENTAL DEVICES Prosthetic Devices § 872.3710 Base metal alloy. (a) Identification. A base metal alloy is a device composed primarily of base metals, such as nickel, chromium, or cobalt, that...

  15. Use of Mg-Al oxide for boron removal from an aqueous solution in rotation: Kinetics and equilibrium studies.

    PubMed

    Kameda, Tomohito; Oba, Jumpei; Yoshioka, Toshiaki

    2016-01-01

    Mg-Al oxide prepared through the thermal treatment of [Formula: see text] intercalated Mg-Al layered double hydroxides (CO3·Mg-Al LDH) was found to remove boron (B) from an aqueous solution. B was removed by the rehydration of Mg-Al oxide accompanied by combination with [Formula: see text] . When using twice the stoichiometric quantity of Mg-Al oxide for Mg/Al = 4, the residual concentration of B dropped from 100 to 2.8 mg/L in 480 min, and for Mg/Al = 2, it decreased from 100 to 2.5 mg/L in 240 min. In both cases, the residual concentration of B was highlighted to be lower than the current Japanese effluent standards (10 mg/L). The removal of B can be explained by way of pseudo-first-order reaction kinetics. The apparent activation energy of 63.5 kJ mol(-1), calculated from the Arrhenius plot indicating that a chemical reaction dominates the removal of B by Mg-Al oxide (Mg/Al = 2). The adsorption of B acts upon a Langmuir-type phenomena. The maximum adsorption (qm) and equilibrium adsorption constants (KL) were 7.4 mmol g(-1) and 1.9 × 10(3), respectively, for Mg-Al oxide (Mg/Al = 2). [Formula: see text] in B(OH)4·Mg-Al LDH produced by the removal of B was observed to undergo anion exchange with [Formula: see text] in solution. Following regeneration, the Mg-Al oxide maintained the ability to remove B from an aqueous solution. This study has clarified the possibility of recycling Mg-Al oxide for B removal.

  16. Three-Ply Al/Mg/Al Clad Sheets Fabricated by Twin-Roll Casting and Post-treatments (Homogenization, Warm Rolling, and Annealing)

    NASA Astrophysics Data System (ADS)

    Park, Jaeyeong; Song, Hyejin; Kim, Jung-Su; Sohn, Seok Su; Lee, Sunghak

    2017-01-01

    When thin Al alloy sheets are clad on to twin-roll-cast Mg alloy melt, inherent drawbacks of Mg alloys such as poor formability, corrosion resistance, and surface quality can be effectively complemented. In this study, three-ply Al/Mg/Al clad sheets were fabricated by twin-roll casting and post-treatments. Brittle interfacial layers composed of γ (Mg17Al12) and β (Mg2Al3) phases were inevitably formed, but their proper thickening during the post-treatments led to improvement of interfacial bonding and resultant tensile properties. In particular, warm rolling was an effective way to modify interfacial microstructures and tensile properties by minimizing deformation inhomogeneity and stress concentration.

  17. 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

  18. Defects and metastable structures of MgAl{sub 2}O{sub 4}

    SciTech Connect

    Chen, S.P.; Yan, M.; Grimes, R.W.; Vyas, S.; Gale, J.D.

    1995-07-01

    This paper presents calculated properties of normal and inverse spinel structures of MgAl{sub 2}O{sub 4} and of point defects in the spinel structure. These results provide information for further study of possible metastable states. Calculated properties of ``amorphous`` structure are also presented. Atomistic simulations show that in MgAl{sub 2}O{sub 4} spinel structure, the exchange of an Mg{sup 2+} ion with an Al{sup 3+} ion has the lowest energy increase, 0. 92eV/atom. The Schottky defect increases the energy by 3.71 eV/atom. Frenkel defects are difficult to form, increasing the energy at least 4.59eV/atom for the Mg{sup 2+} Frenkel defect. Proposed rock salt structure of MgAl{sub 2}O{sub 4} has smaller volume and larger Young modulus, and the amorphosu state has larger volume and smaller Young modulus than the MgAl{sub 2}O{sub 4} spinel.

  19. Synthesis and afterglow properties of MgAl2O4:Eu2+, Dy3+ nanopowders.

    PubMed

    Xu, Xuhui; Wang, Yuhua; Gong, Yu; Li, Yanqin

    2011-11-01

    The MgAl2O4:Eu2+, Dy3+ nanophosphors with different particle sizes have been synthesized through a simple and inexpensive precipitate approach followed by a post-annealing process. The structure and morphology of the phosphor are characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). According to XRD and TEM results, the particle size of MgAl2O4:Eu2+, Dy3+ could be controlled via changing the ratio of MgSO4/Al2O3, and the obtained samples possess regular morphology. The afterglow properties of MgAl2O4:Eu2+, Dy3+ nanophosphors as a function of particle sizes are investigated by afterglow decay curves. Compared with the bulk phosphor, the nanophosphors exhibit longer afterglow time and higher initial afterglow intensity. In nanophosphors, there exist numerous defects on their surfaces due to the large surface to volume ratio, which generally act as luminescent killers, while some of which, however, can probably act as traps beneficial for the generation of afterglow. In the nanosized MgAl2O4:Eu2+, Dy3+ phosphor, the thermoluminescence results indeed indicate the existence of more traps which are introduced due to the large surface to volume ratio of nanoparticles and that the high temperature sintering process contributes to the longer afterglow in the nanophosphors.

  20. Strain relaxation and order-disorder phase transition in irradiated MgAl2O4.

    PubMed

    Kossoy, Anna

    2014-01-07

    MgAl2O4 spinel is widely studied in many fields of material science because of its variety of interesting properties and potential applications. The influence of cation disorder on the physical properties of MgAl2O4 makes understanding of the effects related to this disorder particularly important. It is known that, upon ion irradiation at low temperature, MgAl2O4 undergoes an order-disorder phase transition followed by amorphization. This paper reports a combined high resolution X-ray diffraction and transmission electron microscopy study elucidating the linkage between this phase transition and irradiation-induced elastic strain. Irradiations were carried out on [110] and [111]-oriented single crystals of MgAl2O4 at T = 77 K with 600 keV Xe ions over a wide range of doses. The data suggests that the beginning of the order-disorder phase transition coincides with the beginning of strain relaxation. This result indicates that the volume of the new phase is slightly smaller than that of the unirradiated spinel. The dose at which the phase transformation occurs is found to be dependent on the crystal orientation, which can be attributed to both elastic and crystallographic properties.

  1. Columnar-Structured Mg-Al-Spinel Thermal Barrier Coatings (TBCs) by Suspension Plasma Spraying (SPS)

    NASA Astrophysics Data System (ADS)

    Schlegel, N.; Ebert, S.; Mauer, G.; Vaßen, R.

    2015-01-01

    The suspension plasma spraying (SPS) process has been developed to permit the feeding of sub-micrometer-sized powder into the plasma plume. In contrast to electron beam-physical vapor deposition and plasma spray-physical vapor deposition, SPS enables the cost-efficient deposition of columnar-structured coatings. Due to their strain tolerance, these coatings play an important role in the field of thermal barrier coatings (TBCs). In addition to the cost-efficient process, attention was turned to the TBC material. Nowadays, yttria partially stabilized zirconia (YSZ) is used as standard TBC material. However, its long-term application at temperatures higher than 1200 °C is problematic. At these high temperatures, phase transitions and sintering effects lead to the degradation of the TBC system. To overcome those deficits of YSZ, Mg-Al-spinel was chosen as TBC material. Even though it has a lower melting point (~2135 °C) and a higher thermal conductivity (~2.5 W/m/K) than YSZ, Mg-Al-spinel provides phase stability at high temperatures in contrast to YSZ. The Mg-Al-spinel deposition by SPS resulted in columnar-structured coatings, which have been tested for their thermal cycling lifetime. Furthermore, the influence of substrate cooling during the spraying process on thermal cycling behavior, phase composition, and stoichiometry of the Mg-Al-spinel has been investigated.

  2. Progress in ODS Alloys: A Synopsis of a 2010 Workshop on Fe- Based ODS Alloys

    SciTech Connect

    Kad, Bimal; Dryepondt, Sebastien N; Jones, Andy R.; Vito, Cedro III; Tatlock, Gordon J; Pint, Bruce A; Tortorelli, Peter F; Rawls, Patricia A.

    2012-01-01

    In Fall 2010, a workshop on the role and future of Fe-based Oxide Dispersion Strengthened (ODS) alloys gathered together ODS alloy suppliers, potential industrial end-users, and technical experts in relevant areas. Presentations and discussions focused on the current state of development of these alloys, their availability from commercial suppliers, past major evaluations of ODS alloy components in fossil and nuclear energy applications, and the technical and economic issues attendant to commercial use of ODS alloys. Significant progress has been achieved in joining ODS alloys, with creep resistant joints successfully made by inertia welding, friction stir welding and plasma-assisted pulse diffusion bonding, and in improving models for the prediction of lifetime components. New powder and alloy fabrication methods to lower cost or improve endproduct properties were also described. The final open discussion centered on challenges and pathways for further development and large-scale use of ODS alloys.

  3. The Gaia-ESO Survey. Mg-Al anti-correlation in iDR4 globular clusters

    NASA Astrophysics Data System (ADS)

    Pancino, E.; Romano, D.; Tang, B.; Tautvaišienė, G.; Casey, A. R.; Gruyters, P.; Geisler, D.; San Roman, I.; Randich, S.; Alfaro, E. J.; Bragaglia, A.; Flaccomio, E.; Korn, A. J.; Recio-Blanco, A.; Smiljanic, R.; Carraro, G.; Bayo, A.; Costado, M. T.; Damiani, F.; Jofré, P.; Lardo, C.; de Laverny, P.; Monaco, L.; Morbidelli, L.; Sbordone, L.; Sousa, S. G.; Villanova, S.

    2017-05-01

    We use Gaia-ESO (GES) Survey iDR4 data to explore the Mg-Al anti-correlation in globular clusters that were observed as calibrators, as a demonstration of the quality of Gaia-ESO Survey data and analysis. The results compare well with the available literature, within 0.1 dex or less, after a small (compared to the internal spreads) offset between the UVES and GIRAFFE data of 0.10-0.15 dex was taken into account. In particular, for the first time we present data for NGC 5927, which is one of the most metal-rich globular clusters studied in the literature so far with [ Fe / H ] = - 0.39 ± 0.04 dex; this cluster was included to connect with the open cluster regime in the Gaia-ESO Survey internal calibration. The extent and shape of the Mg-Al anti-correlation provide strong constraints on the multiple population phenomenon in globular clusters. In particular, we studied the dependency of the Mg-Al anti-correlation extension with metallicity, present-day mass,and age of the clusters, using GES data in combination with a large set of homogenized literature measurements.We find a dependency with both metallicity and mass, which is evident when fitting for the two parameters simultaneously, but we do not find significant dependency with age. We confirm that the Mg-Al anti-correlation is not seen in all clusters, but disappears for the less massive or most metal-rich clusters. We also use our data set to see whether a normal anti-correlation would explain the low [Mg/α] observed in some extragalactic globular clusters, but find that none of the clusters in our sample can reproduce it; a more extreme chemical composition, such as that of NGC 2419, would be required. We conclude that GES iDR4 data already meet the requirements set by the main survey goals and can be used to study globular clusters in detail, even if the analysis procedures were not specifically designed for them. Based on data products from observations made with ESO Telescopes at the La Silla Paranal

  4. THERMOSTATICS AND KINETICS OF TRANSFORMATIONS IN PU-BASED ALLOYS

    SciTech Connect

    Turchi, P; Kaufman, L; Liu, Z

    2006-06-30

    CALPHAD assessment of the thermodynamic properties of a series of Pu-based alloys is briefly presented together with some results on the kinetics of phase formation and transformations in Pu-Ga alloys.

  5. Vanadium-base alloys for fusion reactor applications

    SciTech Connect

    Smith, D.L.; Loomis, B.A.; Diercks, D.R.

    1984-10-01

    Vanadium-base alloys offer potentially significant advantages over other candidate alloys as a structural material for fusion reactor first wall/blanket applications. Although the data base is more limited than that for the other leading candidate structural materials, viz., austenitic and ferritic steels, vanadium-base alloys exhibit several properties that make them particularly attractive for the fusion reactor environment. This paper presents a review of the structural material requirements, a summary of the materials data base for selected vanadium-base alloys, and a comparison of projected performance characteristics compared to other candidate alloys. Also, critical research and development (R and D) needs are defined.

  6. Mechanically alloyed Ni-base alloys for heat-resistant applications

    SciTech Connect

    Wilson, R.K.; Fischer, J.J.

    1995-12-31

    INCONEL alloys MA 754 and MA 758 are nickel-base oxide dispersion-strengthened (ODS) alloys made by mechanical alloying (MA). Commercial use of Ma Ni-base alloys to date has been predominantly in aerospace applications of alloy MA 754 as turbine engine vanes. Both alloys are suitable for industrial heat treating components and other heat resistant alloy applications. Field trials and commercial experience in such applications of MA alloys are being gained while high temperature property characterization and new product form development continue. Hot isostatic pressing (HIP) is the standard consolidation method for billets from which large bar and plate are produced for industrial applications of MA. This paper describes production of standard mill shapes from HIP billets, and it presents information on current and potential uses of MA alloys in applications such as: skid rails for use in high temperature walking beam furnaces, heat treating furnace components, components for handling molten glass, and furnace tubes. The paper includes comparison of the properties obtained in alloy MA 754 (20% Cr) and alloy MA 758 (30% Cr).

  7. Effect of monobutylether ethylene glycol on Mg/Al layered double hydroxide: a physicochemical and conductivity study

    NASA Astrophysics Data System (ADS)

    Paulo, Maria Joao; de Matos, Bruno Ribeiro; Ntais, Spyridon; Fonseca, Fabio Coral; Tavares, Ana C.

    2013-02-01

    Mg-Al hydrotalcite-like compounds with OH- ions intercalated in the gallery and modified with monobutylether ethylene glycol ( mbeeg) were prepared from Mg6Al2(CO3)(OH)16·4H2O by the reconstruction method. The effect of the ethylene glycol, a moderate surfactant, on the textural properties and on the vapor water sorption of the layered double hydroxides was investigated by transmission electron microscopy and nitrogen and water sorption techniques. The ion conductivity of the samples was measured at 98 % RH up to 180 °C. The compounds are formed by nanoplatelets with a lateral size inferior to 20 nm. The addition of the ethylene glycol was found to increase the specific surface area, total pore volume, and water sorption capacity of the Mg-Al layered double hydroxide. However, it also decreased the average pore diameter, and the ion conductivity of the ethylene glycol modified layered double hydroxide was lower than expected based on the samples' specific surface area and water content.

  8. Noncontact atomic force microscopy study of the spinel MgAl2O4(111) surface

    PubMed Central

    Rasmussen, Morten K; Meinander, Kristoffer; Besenbacher, Flemming

    2012-01-01

    Summary Based on high-resolution noncontact atomic force microscopy (NC-AFM) experiments we reveal a detailed structural model of the polar (111) surface of the insulating ternary metal oxide, MgAl2O4 (spinel). NC-AFM images reveal a 6√3×6√3R30° superstructure on the surface consisting of patches with the original oxygen-terminated MgAl2O4(111) surface interrupted by oxygen-deficient areas. These observations are in accordance with previous theoretical studies, which predict that the polarity of the surface can be compensated by removal of a certain fraction of oxygen atoms. However, instead of isolated O vacancies, it is observed that O is removed in a distinct pattern of line vacancies reflected by the underlying lattice structure. Consequently, by the creation of triangular patches in a 6√3×6√3R30° superstructure, the polar-stabilization requirements are met. PMID:22496991

  9. 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.

  10. New treatment method for boron in aqueous solutions using Mg-Al layered double hydroxide: Kinetics and equilibrium studies.

    PubMed

    Kameda, Tomohito; Oba, Jumpei; Yoshioka, Toshiaki

    2015-08-15

    Mg-Al layered double hydroxides (LDHs) intercalated with NO3(-) (NO3 · Mg - Al LDHs) and with Cl(-) (Cl · Mg - Al LDHs) were found to take up boron from aqueous solutions. Boron was removed by anion exchange of B(OH)4(-) in solution with NO3(-) and Cl(-) intercalated in the interlayer of the LDH. Using three times the stoichiometric quantity of NO3 · Mg-Al LDH, the residual concentration of B decreased from 100 to 1.9 mg L(-1) in 120 min. Using five times the stoichiometric quantity of Cl · Mg - Al LDH, the residual concentration of B decreased from 100 to 5.6 mg L(-1) in 120 min. It must be emphasized that, in both cases, the residual concentration of B was less than the effluent standards in Japan (10 mg L(-1)). The rate-determining step of B removal by the NO3 · Mg - Al and Cl · Mg - Al LDHs was found to be chemical adsorption involving anion exchange of B(OH)4(-) with intercalated NO3(-) and Cl(-). The removal of B was well described by a pseudo second-order kinetic equation. The adsorption of B by NO3 · Mg - Al LDH and Cl · Mg - Al LDH followed a Langmuir-type adsorption. The values of the maximum adsorption and the equilibrium adsorption constant were 3.6 mmol g(-1) and 1.7, respectively, for NO3 · Mg - Al LDH, and 3.8 mmol g(-1) and 0.7, respectively, for Cl · Mg-Al LDH. The B(OH)4(-) in B(OH)4 · Mg - Al LDH produced by removal of B was found to undergo anion exchange with NO3(-) and Cl(-) in solution. The NO3 · Mg - Al and Cl · Mg - Al LDHs obtained after this regeneration treatment were able to remove B from aqueous solutions, indicating the possibility of recycling NO3 · Mg - Al and Cl · Mg - Al LDHs for B removal.

  11. Theoretical Investigation of the Structural, Elastic, and Thermodynamic Properties of MgAl2O4 Spinel under High Pressure

    NASA Astrophysics Data System (ADS)

    Mao, Xiao-Chun; Liu, Ke; Hou, Bao-Sen; Tan, Jiao; Zhou, Xiao-Lin

    2016-11-01

    The structural and elastic properties of MgAl2O4 spinel under high pressure are investigated through the first-principles calculations. The lattice parameters and elastic constants are in good agreement with the available experimental and theoretical results. The polycrystalline elastic moduli of MgAl2O4 spinel are calculated using the Voigt-Reuss-Hill approximation. By the elastic stability criteria, the MgAl2O4 spinel is mechanically stable within 80 GPa. MgAl2O4 possesses ductile nature, and the ductility is enhanced with the increase of pressure. The sound velocities over a wide range of pressures are also obtained. Furthermore, the elastic anisotropies of MgAl2O4 are investigated via the various anisotropic indexes and the 3D surface constructions. It is found that MgAl2O4 is isotropic for bulk modulus, while is anisotropic for shear modulus and Young's modulus, and the elastic anisotropy of MgAl2O4 increases due to the applying pressure. Besides, the directions with smaller values of shear modulus for MgAl2O4 will deform preferentially under high hydrostatic pressure. Through the quasi-harmonic Debye model, we also investigated the thermodynamic properties of MgAl2O4 spinel.

  12. 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.

  13. 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.

  14. [NOx storage and decomposition behavior of Cu-Mg-Al catalyst].

    PubMed

    Kang, Shou-fang; Li, Jun-hua; Fu, Li-xin; Hao, Zheng-ping

    2007-05-01

    Cu-Mg-Al hydrotalcite mixed oxide was prepared by co-precipitation. The mixed oxide and its procurer were characterized by XRD. NO, storage performance and decomposition of the stored NO, over the catalyst were investigated by NO, storage experiment at constant temperature, temperature programmed desorption (TPD) and temperature programmed surface reaction (TPSR), respectively. The results indicate that Cu-Mg-Al hydrotalcite mixed oxide has a good performance of NO, storage. The formed nitrate can be decomposed to gaseous NOx rapidly in the investigated temperature range of 160-360 degrees C, and a small amount of gaseous NO, can be reduced by C3 H6 with increasing the concentration of C3 H6 in the inlet gas.

  15. Direct observation of grafting interlayer phosphate in Mg/Al layered double hydroxides

    SciTech Connect

    Shimamura, Akihiro; Kanezaki, Eiji; Jones, Mark I.; Metson, James B.

    2012-02-15

    The grafting of interlayer phosphate in synthetic Mg/Al layered double hydroxides with interlayer hydrogen phosphate (LDH-HPO{sub 4}) has been studied by XRD, TG/DTA, FT-IR, XPS and XANES. The basal spacing of crystalline LDH-HPO{sub 4} decreases in two stages with increasing temperature, from 1.06 nm to 0.82 nm at 333 K in the first transition, and to 0.722 nm at 453 K in the second. The first stage occurs due to the loss of interlayer water and rearrangement of the interlayer HPO{sub 4}{sup 2-}. In the second transition, the interlayer phosphate is grafted to the layer by the formation of direct bonding to metal cations in the layer, accompanied by a change in polytype of the crystalline structure. The grafted phosphate becomes immobilized and cannot be removed by anion-exchange with 1-octanesulfonate. The LDH is amorphous at 743 K but decomposes to Mg{sub 3}(PO{sub 4}){sub 2}, AlPO{sub 4}, MgO and MgAl{sub 2}O{sub 4} after heated to 1273 K. - Graphical abstract: The cross section of the synthetic Mg, Al layered double hydroxides in Phase 1, with interlayer hydrogen phosphate Phase 2, and with grafted phosphate, Phase 3. Highlights: Black-Right-Pointing-Pointer The grafting of hydrogen phosphate intercalated Mg/Al-LDH has been studied. Black-Right-Pointing-Pointer The basal spacing of crystalline LDH-HPO{sub 4} decreases in two stages with increasing temperature. Black-Right-Pointing-Pointer The first decrease is due to loss of interlayer water, the second is attributed to phosphate grafting. Black-Right-Pointing-Pointer The grafted interlayer phosphate becomes immobilized and cannot be removed by anion-exchange.

  16. Composition driven monolayer to bilayer transformation in a surfactant intercalated Mg-Al layered double hydroxide.

    PubMed

    Naik, Vikrant V; Chalasani, Rajesh; Vasudevan, S

    2011-03-15

    The structure and organization of dodecyl sulfate (DDS) surfactant chains intercalated in an Mg-Al layered double hydroxide (LDH), Mg(1-x)Alx(OH)2, with differing Al/Mg ratios has been investigated. The Mg-Al LDHs can be prepared over a range of compositions with x varying from 0.167 to 0.37 and therefore provides a simple system to study how the organization of the alkyl chains of the intercalated DDS anions change with packing density; the Al/Mg ratio or x providing a convenient handle to do so. Powder X-ray diffraction measurements showed that at high packing densities (x ≥ 0.3) the alkyl chains of the intercalated dodecyl sulfate ions are anchored on opposing LDH sheets and arranged as bilayers with an interlayer spacing of ∼27 Å. At lower packing densities (x < 0.2) the surfactant chains form a monolayer with the alkyl chains oriented flat in the galleries with an interlayer spacing of ∼8 Å. For the in between compositions, 0.2 ≤ x < 0.3, the material is biphasic. MD simulations were performed to understand how the anchoring density of the intercalated surfactant chains in the Mg-Al LDH-DDS affects the organization of the chains and the interlayer spacing. The simulations are able to reproduce the composition driven monolayer to bilayer transformation in the arrangement of the intercalated surfactant chains and in addition provide insights into the factors that decide the arrangement of the surfactant chains in the two situations. In the bilayer arrangement, it is the dispersive van der Waals interactions between chains in opposing layers of the anchored bilayer that is responsible for the cohesive energy of the solid whereas at lower packing densities, where a monolayer arrangement is favored, Coulomb interactions between the positively charged Mg-Al LDH sheets and the negatively charged headgroup of the DDS anion dominate.

  17. Advanced alloy design technique: High temperature cobalt base superalloy

    NASA Technical Reports Server (NTRS)

    Dreshfield, R. L.; Freche, J. C.; Sandrock, G. D.

    1972-01-01

    Advanced alloy design technique was developed for treating alloys that will have extended life in service at high temperature and intermediate temperatures. Process stabilizes microstructure of the alloy by designing it so that compound identified with embrittlement is eliminated or minimized. Design process is being used to develop both nickel and cobalt-base superalloys.

  18. Characterization of two ceramic-base-metal alloys.

    PubMed

    Huget, E F; Vlica, J M; Wall, R M

    1978-12-01

    Compositions, microstructures, properties, and heat treatment characteristics of two ceramic-base-metal alloys were studied. The materials displayed significant compositional and structural differences. Both alloys were strengthened by precipitation hardening. Strength and rigidity of the nickel-chromium alloys suggest their potential usefulness in fixed prosthodontic procedures.

  19. Unique mechanical properties of nanostructured transparent MgAl2O4 ceramics.

    PubMed

    Zhang, Jie; Lu, Tiecheng; Chang, Xianghui; Wei, Nian; Qi, Jianqi

    2013-06-01

    Nanoindentation tests were performed on nanostructured transparent magnesium aluminate (MgAl2O4) ceramics to determine their mechanical properties. These tests were carried out on samples at different applied loads ranging from 300 to 9,000 μN. The elastic recovery for nanostructured transparent MgAl2O4 ceramics at different applied loads was derived from the force-depth data. The results reveal a remarkable enhancement in plastic deformation as the applied load increases from 300 to 9,000 μN. After the nanoindetation tests, scanning probe microscope images show no cracking in nanostructured transparent MgAl2O4 ceramics, which confirms the absence of any cracks and fractures around the indentation. Interestingly, the flow of the material along the edges of indent impressions is clearly presented, which is attributed to the dislocation introduced. High-resolution transmission electron microscopy observation indicates the presence of dislocations along the grain boundary, suggesting that the generation and interaction of dislocations play an important role in the plastic deformation of nanostructured transparent ceramics. Finally, the experimentally measured hardness and Young's modulus, as derived from the load-displacement data, are as high as 31.7 and 314 GPa, respectively.

  20. First-principles calculations on Mg/Al4C3 interfaces

    NASA Astrophysics Data System (ADS)

    Li, K.; Sun, Z. G.; Wang, F.; Zhou, N. G.; Hu, X. W.

    2013-04-01

    In order to explore the interfacial structure of Mg/Al4C3 interface and clarify the heterogeneous nucleation potential of Al4C3 particles in Mg melt. The atomic structure, bonding, and interfacial energy of Mg/Al4C3 interfaces were studied by first-principles calculations to analyze the sequence of Mg atoms onto the surface of Al4C3 (0 0 0 1) slab. Surface energy calculations show that the outmost layer of Al4C3 free surface having a preference of C atom termination. And polar covalent/ionic mixed bonds are formed across interface during the combination of Mg atoms with C-terminated Al4C3 surface. The calculated interfacial energy of Mg/Al4C3 interface is much smaller than that between α-Mg and magnesium melts, proving the excellent nucleation potency of Al4C3 particles for α-Mg grains from interfacial atomic structure and atomic bonding energy considerations.

  1. Adsorption of methyl orange from aqueous solutions by calcined ZnMgAl hydrotalcite

    NASA Astrophysics Data System (ADS)

    Yuan, Dong; Zhou, Liangqin; Fu, Dayou

    2017-02-01

    The calcined ZnMgAl hydrotalcite was used for degration of methyl orange (MO). The adsorbent was characterized by XRD, SEM, and FT-IR. The results reveal that the ZnMgAl layered structures were disappeared after calcining for 5 h at 500 °C, then were recovered to layer hydrotalcite structure after adsorbing MO anions. The several important affecting factors of adsorption behavior, including the initial pH value of solution, adsorbent dosage, and the initial concentration of solution, were also discussed. The adsorption kinetic processes were fitted with the equations of pseudo-first-order, pseudo-second-order, and intraparticle diffusion, respectively, in which the pseudo-second-order equation fitting results was the better. The equilibrium isotherm of MO was described by both Langmuir and Freundlich model, but better complys with the Langmuir model ( R 2 > 0.98). The possible adsorption mechanism has been presumed. The adsorption experiments indicated that the ZnMgAl hydrotalcite had good adsorption ability to methyl orange in wastewater.

  2. Czochralski growth and characterization of MgAl2O4 single crystals

    NASA Astrophysics Data System (ADS)

    Bajor, Andrzej L.; Chmielewski, Marcin; Diduszko, Ryszard; Kisielewski, Jaroslaw; Lukasiewicz, Tadeusz; Orlinski, Krzysztof; Romaniec, Magdalena; Szyrski, Wlodzimierz

    2014-09-01

    MgAl2O4 (MALO) single crystals were pulled by the Czochralski method in [111] direction. The crystals were doped with Co (0.06-0.6 at% (charge compositions)), because Co2+ ions in tetrahedral positions exhibit non-linear optical properties, and, currently, Co:MALO seems to be the best saturable absorber in the eye-safe region (ca. 1.5 μm). By XRD powder technique a stoichiometric MALO was evidenced without admixtures of higher order spinels (MgAl4O7 and MgAl6O10). Also no excessive residual stresses have been discovered by different optical methods, and irrespective of the doping level we did not face any problem of cracking when cutting the crystals into wafers and other structures. In this work we have concentrated our efforts on investigation of thermal properties of MALO. Due to the 2nd order phase transition ca. 650 °C they seem to be of crucial importance in future thermal bonding of this material to the lasing host (Yb,Er-glass) expected just about this temperature.

  3. Unique mechanical properties of nanostructured transparent MgAl2O4 ceramics

    PubMed Central

    2013-01-01

    Nanoindentation tests were performed on nanostructured transparent magnesium aluminate (MgAl2O4) ceramics to determine their mechanical properties. These tests were carried out on samples at different applied loads ranging from 300 to 9,000 μN. The elastic recovery for nanostructured transparent MgAl2O4 ceramics at different applied loads was derived from the force-depth data. The results reveal a remarkable enhancement in plastic deformation as the applied load increases from 300 to 9,000 μN. After the nanoindetation tests, scanning probe microscope images show no cracking in nanostructured transparent MgAl2O4 ceramics, which confirms the absence of any cracks and fractures around the indentation. Interestingly, the flow of the material along the edges of indent impressions is clearly presented, which is attributed to the dislocation introduced. High-resolution transmission electron microscopy observation indicates the presence of dislocations along the grain boundary, suggesting that the generation and interaction of dislocations play an important role in the plastic deformation of nanostructured transparent ceramics. Finally, the experimentally measured hardness and Young’s modulus, as derived from the load–displacement data, are as high as 31.7 and 314 GPa, respectively. PMID:23724845

  4. New Developments of Ti-Based Alloys for Biomedical Applications

    PubMed Central

    Li, Yuhua; Yang, Chao; Zhao, Haidong; Qu, Shengguan; Li, Xiaoqiang; Li, Yuanyuan

    2014-01-01

    Ti-based alloys are finding ever-increasing applications in biomaterials due to their excellent mechanical, physical and biological performance. Nowdays, low modulus β-type Ti-based alloys are still being developed. Meanwhile, porous Ti-based alloys are being developed as an alternative orthopedic implant material, as they can provide good biological fixation through bone tissue ingrowth into the porous network. This paper focuses on recent developments of biomedical Ti-based alloys. It can be divided into four main sections. The first section focuses on the fundamental requirements titanium biomaterial should fulfill and its market and application prospects. This section is followed by discussing basic phases, alloying elements and mechanical properties of low modulus β-type Ti-based alloys. Thermal treatment, grain size, texture and properties in Ti-based alloys and their limitations are dicussed in the third section. Finally, the fourth section reviews the influence of microstructural configurations on mechanical properties of porous Ti-based alloys and all known methods for fabricating porous Ti-based alloys. This section also reviews prospects and challenges of porous Ti-based alloys, emphasizing their current status, future opportunities and obstacles for expanded applications. Overall, efforts have been made to reveal the latest scenario of bulk and porous Ti-based materials for biomedical applications. PMID:28788539

  5. Removal of HCl, SO₂, and NO by treatment of acid gas with Mg-Al oxide slurry.

    PubMed

    Kameda, Tomohito; Uchiyama, Naoya; Yoshioka, Toshiaki

    2011-01-01

    Although effective treatment of acid gases such as HCl, SO(x), and NO(x) is essential for preventing air pollution, current methods pose other environmental problems such as CaCl₂ leaching, reduced landfill lifetimes, and solid waste production. Here we show that acid gases can be treated simply with a Mg-Al oxide slurry. The contribution of Mg-Al oxide to HCl and SO₂ removal increased as a function of the quantity and temperature of Mg-Al oxide. HCl was removed by the reconstruction of Mg-Al layered double hydroxide (Mg-Al LDH) intercalated with Cl⁻ dissociated from HCl in the slurry. SO₂ was oxidized into SO₃ by oxygen in the air flow, dissolved in an aqueous solution, and removed by the reconstruction of Mg-Al LDH intercalated with dissociated SO₄²⁻. Although less pronounced because of surface adsorption, NO was nonetheless removed by Mg-Al oxide. Our results suggest that simultaneous removal of HCl, SO₂, and NO using a Mg-Al oxide slurry may be possible without the concomitant problems of conventional treatment methods. Copyright © 2010 Elsevier Ltd. All rights reserved.

  6. Use of Raman spectroscopy to assess the efficiency of MgAl mixed oxides in removing cyanide from aqueous solutions

    NASA Astrophysics Data System (ADS)

    Cosano, Daniel; Esquinas, Carlos; Jiménez-Sanchidrián, César; Ruiz, José Rafael

    2016-02-01

    Calcining magnesium/aluminium layered double hydroxides (Mg/Al LDHs) at 450 °C provides excellent sorbents for removing cyanide from aqueous solutions. The process is based on the "memory effect" of LDHs; thus, rehydrating a calcined LDH in an aqueous solution restores its initial structure. The process, which conforms to a first-order kinetics, was examined by Raman spectroscopy. The metal ratio of the LDH was found to have a crucial influence on the adsorption capacity of the resulting mixed oxide. In this work, Raman spectroscopy was for the first time use to monitor the adsorption process. Based on the results, this technique is an effective, expeditious choice for the intended purpose and affords in situ monitoring of the adsorption process. The target solids were characterized by using various instrumental techniques including X-ray diffraction spectroscopy, which confirmed the layered structure of the LDHs and the periclase-like structure of the mixed oxides obtained by calcination.

  7. DISPERSION STRENGTHENED NICKEL-BASE ALLOYS.

    DTIC Science & Technology

    The swaged cone of extruded Nichrome-thoria alloys prepared by the thermal decomposition of thorium nitrate onto alloy powder indicated descreased... swaging of these dispersion-strengthened Nichrome alloys was dependent on the presence of a mild steel jacket on the alloy rod as a result of the canned...extrusion practice. Efforts to cold swage the alloy materials without this jacket were unsuccessful. (Author)

  8. Synthesis of MgAl2O4 spinel nanoparticles using a mixture of bayerite and magnesium sulfate

    NASA Astrophysics Data System (ADS)

    Su, Xinghua; Du, Xuelian; Li, Suqiang; Li, Jiangong

    2010-06-01

    This article reports a novel method to prepare MgAl2O4 spinel nanoparticles. By calcining a powder mixture of bayerite and magnesium sulfate at 800 °C and washing with water, single-phase MgAl2O4 spinel nanoparticles were prepared. The powder mixture and the calcined products were characterized by differential thermal and thermogravimetric analysis (DSC-TG), X-ray diffraction (XRD), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) nitrogen-gas adsorption method. The obtained MgAl2O4 spinel nanoparticles have an average particle size of 12 nm, a narrow size distribution, and weak agglomeration. The specific surface area of the MgAl2O4 spinel powder is 110 m2/g. The formation of MgAl2O4 spinel is attributed to a solid-state reaction between γ-Al2O3 and MgSO4.

  9. X-ray Diffraction Analysis on Post Treatment of Ca-Mg-Al-Layered Double Hydroxide Slurry

    NASA Astrophysics Data System (ADS)

    Heraldy, E.; Nugrahaningtyas, K. D.; Heriyanto

    2017-02-01

    This research objectives to study post treatment on Ca-Mg-Al-Layered Double Hydroxide (Ca-Mg-Al-LDH) slurry which was prepared from brine water by cooling treatment. The cooling rate was varied from 1 to 3 °C/min by using stirring and without stirring, and the cooling time was done at 0, 30 minutes and 24 hours. The quantitative X-ray diffraction (QXRD) was employed on Ca-Mg-Al-LDH using Le Bail refinement method. The refinement results found another Mg-Al-LDH and Ca-Al-LDH phases, such as Mg(OH)2, Al(OH)3 and CaCO3. The highest phase composition on material Ca-Mg-Al-LDH using Le Bail refinement was showed by Al(OH)3.

  10. MgAl2O4 spinel refractory as containment liner for high-temperature alkali salt containing environments

    DOEpatents

    Peascoe-Meisner, Roberta A [Knoxville, TN; Keiser, James R [Oak Ridge, TN; Hemric, James G [Knoxville, TN; Hubbard, Camden R [Oak Ridge, TN; Gorog, J Peter [Kent, WA; Gupta, Amul [Jamestown, NY

    2008-10-21

    A method includes containing a high-temperature alkali salt containing environment using a refractory containment liner containing MgAl.sub.2O.sub.4 spinel. A method, includes forming a refractory brick containing MgAl.sub.2O.sub.4 spinel having an exterior chill zone defined by substantially columnar crystallization and an interior zone defined by substantially equiaxed crystallization; and removing at least a portion of the exterior chill zone from the refractory brick containing MgAl.sub.2O.sub.4 spinel by scalping the refractory brick containing MgAl.sub.2O.sub.4 spinel to define at least one outer surface having an area of substantially equiaxed crystallization. A product of manufacture includes a refractory brick containing MgAl.sub.2O.sub.4 spinel including an interior zone defined by substantially equiaxed crystallization; and at least one outer surface having an area of substantially equiaxed crystallization.

  11. Structural and spectroscopic properties of Li+ co-doped MgAl2O4: Eu3+ nanophosphors

    NASA Astrophysics Data System (ADS)

    Faizan, Mohd.; Ahmad, Shabbir

    2016-05-01

    The red light emitting highly-luminescent Li+ co-doped magnesium aluminates (MgAl2O4: Eu3+) nanophosphors were synthesized by combustion synthesis method. The phosphors were characterized by XRD, FTIR, UV-visible and photoluminescence (PL) spectroscopy. The crystal structure and phase of the phosphors were investigated using XRD. The band gap of pure, Eu3+ doped and Li+ codoped MgAl2O4 phosphor were obtained from the DR spectra using the K-M function F(R∞). The photoluminescence spectra of MgAl2O4:Eu3+ and Li+ codoped MgAl2O4:Eu3+ phosphors were described by well known 5D0-7Fj transitions (J=0, 1, 2, 3, 4). The emission intensity of MgAl2O4:Eu3+ phosphor is enhanced with Li+ codoping.

  12. Grain Refinement of Permanent Mold Cast Copper Base Alloys

    SciTech Connect

    M.Sadayappan; J.P.Thomson; M.Elboujdaini; G.Ping Gu; M. Sahoo

    2005-04-01

    Grain refinement is a well established process for many cast and wrought alloys. The mechanical properties of various alloys could be enhanced by reducing the grain size. Refinement is also known to improve casting characteristics such as fluidity and hot tearing. Grain refinement of copper-base alloys is not widely used, especially in sand casting process. However, in permanent mold casting of copper alloys it is now common to use grain refinement to counteract the problem of severe hot tearing which also improves the pressure tightness of plumbing components. The mechanism of grain refinement in copper-base alloys is not well understood. The issues to be studied include the effect of minor alloy additions on the microstructure, their interaction with the grain refiner, effect of cooling rate, and loss of grain refinement (fading). In this investigation, efforts were made to explore and understand grain refinement of copper alloys, especially in permanent mold casting conditions.

  13. Cast Fe-base cylinder/regenerator housing alloy

    NASA Technical Reports Server (NTRS)

    Larson, F.; Kindlimann, L.

    1980-01-01

    The development of an iron-base alloy that can meet the requirements of automotive Stirling engine cylinders and regenerator housings is described. Alloy requirements are as follows: a cast alloy, stress for 5000-hr rupture life of 200 MPa (29 ksi) at 775 C (1427 F), oxidation/corrosion resistance comparable to that of N-155, compatibility with hydrogen, and an alloy cost less than or equal to that of 19-9DL. The preliminary screening and evaluation of ten alloys are described.

  14. Crystal Chemistry of MgAl2O4 Spinel Solid Solution

    NASA Astrophysics Data System (ADS)

    Yoshiasa, Akira; Maekawa, Hidemi; Sugiyama, Kazumasa

    Considerable efforts have been devoted to the structural studies of spinel group minerals or type compounds because of their importance as constituents of the Earth’s crust and mantle. Despite their simple structures, many spinel type compounds exhibit complex disordering phenomena involving the mixing of cation on two sites, which have important consequences for both thermodynamic and physical properties. The cation distributions and the structural variation in MgAl2-xGaxO4 solid-solution have been clarified using 27Al MAS NMR measurements and single crystal X-ray diffraction. The determined local distance in the solid solution corresponds with the bond distance expected from the effective ionic radii except Al-O distance in the tetrahedral site. We have revealed that the Al-O distance in the tetrahedral site in spinel solid solution is about 0.15 Å longer than the expected value. Boron is the same group element as Al and Ga and its ionic radius is considerably small. Single crystals of MgAl2-xBxO4 spinel were synthesized under high pressure and high temperature. The maximum content of boron was about x = 0.13 at 1273 K and 11 GPa. The smallest B ion occupies the octahedral site in top priority in the spinel solid solution of the Mg-Al-B systems. The B3+ ions can replace considerably bigger Al3+ ion under pressure. These spinel solid-solutions are largely disordered crystals. Only the positional shifts of oxygen ion have been relaxing the disorder in the solid solution.

  15. A hybrid Mg-Al layered double hydroxide/graphene nanostructure obtained via hydrothermal synthesis

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaodong; Cao, Jian-Ping; Zhao, Jun; Hu, Guo-Hua; Dang, Zhi-Min

    2014-06-01

    A hybrid Mg-Al layered double hydroxide/graphene (LDH-GR) material nanostructure has been fabricated by employing the hydrothermal treatment at 140 °C for 10 h. Graphene oxide is simultaneously reduced to graphene during the hydrothermal treatment. The LDH and LDH-GR have high degree of crystallinity and assembled layer structure, which is attributed to electrostatic interaction mechanism. The obtained hybrid nanostructure materials can be used as flame retardant or conductor of electricity and heat due to the combination of different properties arising from graphene and LDH.

  16. Thermodynamic properties of spinel MgAl2O4: A mass spectrometric study

    NASA Astrophysics Data System (ADS)

    Shornikov, S. I.

    2017-02-01

    The activities of oxides in stoichiometric spinel MgAl2O4 in the temperature range 1851-2298 K were determined from the data obtained by the Knudsen effusion mass spectrometry. The resulting Gibbs energies of spinel formation from simple oxides, the enthalpies and entropies of spinel formation from simple oxides (-12.02 ± 1.14 kJ/mol and 5.03 ± 0.56 J/(mol K), respectively), and the spinel melting enthalpy (55.81 ± 4.62 kJ/mol) satisfactorily agree with the available thermodynamic data.

  17. Kinetic Research on Catalytic Degradation of Rhodamine B with Cobalt Phthalocyanine Supported Mg-Al Hydrotalcite.

    PubMed

    Xu, Minhong; Cao, Yongyong; Ma, Xinyue

    2016-01-01

    Rhodamine B dye wastewater was degraded using cobalt phthalocyanine supported Mg-Al hydrotal- cite and H₂O₂. The effects of H₂O₂, temperature and concentration of Rhodamine B on the reaction kinetics were studied. The results indicate that the degradation process conforms to the equation of first order kinetics. The fastest rate constant k observed was 66.2 x 10⁻⁴/min⁻¹ at 62.5 °C, and the correlation coefficient R2 was 0.99733.

  18. Li-substituted MgAl2O4 barriers for spin-dependent coherent tunneling

    NASA Astrophysics Data System (ADS)

    Scheike, Thomas; Sukegawa, Hiroaki; Mitani, Seiji

    2016-11-01

    Epitaxial magnetic tunnel junctions (MTJs) with a Li-substituted spinel MgAl2O4 barrier were prepared by sputtering and plasma oxidation of an Mg/LiAl bilayer. The formed MTJ with Fe(001) electrodes showed a relatively large tunnel magnetoresistance (TMR) ratio of 120% (174%) at room temperature (3 K) and two local minima in the tunneling conductance spectra (parallel magnetization), revealing the occurrence of the coherent tunneling effect through the Li-substituted spinel barrier. The results are likely to pave the way for a variety of quaternary spinel oxide barriers in which structural and transport properties of MTJs can be engineered in the coherent tunneling regime.

  19. 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).

  20. Casting Accuracy of Base-Metal Alloys,

    DTIC Science & Technology

    1981-06-22

    Journal of Prosthodontic Dentistry I.I. SUPPLEMENTARY NOTES ".KL... prosthodontics ; however, the inabilitv to fabricate consistently well fitting fixed prostheses from base-metal alloysS- 7 limit tihe routine use of these...q4- 0 A sm 0 cm CAb F -rr-- I............ 0< Loa,,.’..’ . .- . ... CI w~ cc~ 0 00 (0 Iq on 0 D 0M 0J 004 0 0a .~ .D ....... L .......... (%l) AovdlDov LDNIISV2D 0 Jic r,4wC 0JLL 0 0000 0 co to (%l) ADv /nflDDv cDNIiSVD

  1. Toughening mechanisms in Mg/Al macrocomposites: texture and interfacial mechanical interlocking

    NASA Astrophysics Data System (ADS)

    Paramsothy, M.; Hassan, S. F.; Srikanth, N.; Gupta, M.

    2008-09-01

    In this study, two types of new bimetal magnesium/aluminium (Mg/Al) macrocomposites with millimetre-scale Al core reinforcement were fabricated using casting coupled with hot coextrusion. The first macrocomposite was fabricated with an unthreaded Al core while the second one had a threaded Al core. Microstructural characterization revealed Mg texture change and interdiffusion of Mg and Al into each other across the interface in an unbalanced manner. Stress at the bimetal interface was attributed to solid solution formation, thermal expansion mismatch, unbalanced Kirkendall strain, lattice misfit strain and strain localization effects. Results revealed that the presence of the Al core leads to a decrease in strength but an increase in failure strain and toughness (work of fracture) of Mg. The threaded Al core reduced 0.2%YS and UTS of Mg by 17% and 15%, respectively, and enhanced the failure strain and toughness of Mg by 102% and 73%, respectively. This was 1.4 and 1.6 times less the reduction, and about 6 and 7 times more the increment, when compared with the corresponding changes of 0.2%YS, UTS, failure strain and toughness of the unthreaded macrocomposite, respectively. The toughening mechanisms in bimetal Mg/Al macrocomposites are investigated in this paper.

  2. Nanoscale analysis of surface oxides on ZnMgAl hot-dip-coated steel sheets.

    PubMed

    Arndt, M; Duchoslav, J; Itani, H; Hesser, G; Riener, C K; Angeli, G; Preis, K; Stifter, D; Hingerl, K

    2012-05-01

    In this work, the first few nanometres of the surface of ZnMgAl hot-dip-galvanised steel sheets were analysed by scanning Auger electron spectroscopy, angle-resolved X-ray photoelectron spectroscopy and atomic force microscopy. Although the ZnMgAl coating itself is exhibiting a complex micro-structure composed of several different phases, it is shown that the topmost surface is covered by a smooth, homogeneous oxide layer consisting of a mixture of magnesium oxide and aluminium oxide, exhibiting a higher amount of magnesium than aluminium and a total film thickness of 4.5 to 5 nm. Especially by the combined analytical approach of surface-sensitive methods, it is directly demonstrated for the first time that within surface imprints--created by industrial skin rolling of the steel sheet which ensures a smooth surface appearance as well as reduced yield-point phenomenon--the original, smooth oxide layer is partly removed and that a layer of native oxides, exactly corresponding to the chemical structure of the underlying metal phases, is formed.

  3. Mg-Al layered double hydroxide intercalated with porphyrin anions: molecular simulations and experiments.

    PubMed

    Kovár, Petr; Pospísil, Miroslav; Káfunková, Eva; Lang, Kamil; Kovanda, Frantisek

    2010-02-01

    Molecular modeling in combination with powder X-ray diffraction (XRD) provided new information on the organization of the interlayer space of Mg-Al layered double hydroxide (LDH) containing intercalated porphyrin anions [5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS)]. Anion-exchange and rehydration procedures were used for the preparation of TPPS-containing LDH with an Mg/Al molar ratio of 2. Molecular modeling was carried out in the Cerius(2) and Materials Studio modeling environment. Three types of models were created in order to simulate the experimental XRD patterns of LDH intercalates with a TPPS loading of 70-80% with respect to the theoretical anion exchange capacity (AEC). The models represent single-phase systems with a 100% TPPS loading in the interlayer space (Type 1) and models represent the coexistence of two phases corresponding to the total exchange from 75 to 92% (Type 2). To cover other possible arrangements, models with the coexistence of both TPPS and NO(3)(-) anions in the same interlayer space were calculated (Type 3). The models are described and compared with experimental data. In all cases, guest TPPS anions are tilted with respect to the hydroxide layers, and are horizontally shifted to each other by up to one-half of the TPPS diameter. According to the energy characteristics and simulated XRD, the most probable arrangement is of Type 2, where some layers are saturated with TPPS anions and others are filled with original NO(3)(-) anions.

  4. Metastability in the MgAl2O4-Al2O3 System

    DOE PAGES

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

    2014-07-22

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

  5. Preparation of SiC–MgAl2O4–Y3Al5O12-MWCNTs nanocomposites by spark plasma sintering

    NASA Astrophysics Data System (ADS)

    Zharikov, E. V.; Kapustin, V. V.; Faikov, P. P.; Popova, N. A.; Barmin, A. A.; Ivanov, A. V.; Rizakhanov, R. N.

    2017-02-01

    Fabrication a composite materials based on silicon carbide (SiC) reinforced with multi-walled carbon nanotubes (MWCNTs) with addition of magnesium alumina spinel MgAl2O4, and yttrium aluminum garnet Y3Al5O12 by spark plasma sintering are presented. Two series of composites differing by the particle size of starting SiC were prepared. Mechanical characteristics of composites including microhardness, fracture toughness and flexural strength are determined.

  6. Castability optimization of palladium based alloys.

    PubMed

    Cohen, S M; Kakar, A; Vaidyanathan, T K; Viswanadhan, T

    1996-08-01

    Poor or inconsistent castability often necessitates costly laboratory remakes of cast restorations. This study investigated the effects of burnout temperature and alloy investment compatibility on the castability of selected alloys. In part A nine alloy investment combinations were compared. In part B two alloy-investment combinations at four burnout temperatures were evaluated. Differences in investment, alloy, and/or burnout temperature significantly affected castability. Castability with a poorer casting investment improved with a hotter propane/oxygen fuel source compared with natural (city) gas/oxygen.

  7. Studies of the optical and EPR data and the defect structure for the trigonal Cr3+ center in LaMgAl11O19 crystal

    NASA Astrophysics Data System (ADS)

    Yang, Li-Rong; Liu, Chang; Mei, Yang; Zheng, Wen-Chen

    2017-04-01

    The complete diagonalization (of energy matrix) method based on the two-spin-orbit-parameter model (which takes into account of the contributions from both the spin-orbit parameter of dn ions in the traditional crystal field theory and that of ligand ions via covalence effect) is adopted to calculate uniformly the optical and EPR data of the trigonal Cr3+ center in LaMgAl11O19 crystal. The calculated results demonstrate that the observed nine optical and EPR data (six optical bands and three spin-Hamiltonian parameters g//, g⊥ and D) can be explained reasonably, which proves the effectiveness and practicality of the method in the unified calculations of optical and EPR data for crystals doped with d3 ions. The defect structure of Cr3+ center in LaMgAl11O19 crystal due to the size mismatch is also estimated.

  8. Cast iron-base alloy for cylinder/regenerator housing

    NASA Technical Reports Server (NTRS)

    Witter, Stewart L.; Simmons, Harold E.; Woulds, Michael J.

    1985-01-01

    NASACC-1 is a castable iron-base alloy designed to replace the costly and strategic cobalt-base X-40 alloy used in the automotive Stirling engine cylinder/generator housing. Over 40 alloy compositions were evaluated using investment cast test bars for stress-rupture testing. Also, hydrogen compatibility and oxygen corrosion resistance tests were used to determine the optimal alloy. NASACC-1 alloy was characterized using elevated and room temperature tensile, creep-rupture, low cycle fatigue, heat capacity, specific heat, and thermal expansion testing. Furthermore, phase analysis was performed on samples with several heat treated conditions. The properties are very encouraging. NASACC-1 alloy shows stress-rupture and low cycle fatigue properties equivalent to X-40. The oxidation resistance surpassed the program goal while maintaining acceptable resistance to hydrogen exposure. The welding, brazing, and casting characteristics are excellent. Finally, the cost of NASACC-1 is significantly lower than that of X-40.

  9. Correlation of dark mantle deposits with high Mg/Al ratios. [from orbital X-ray fluorescence experiment on moon

    NASA Technical Reports Server (NTRS)

    Schonfeld, E.; Bielefeld, M. J.

    1978-01-01

    The Mg/Al concentration ratios from the orbital fluorescence X-ray experiment were used to characterize dark mantle deposits on the moon. The areas studied included the regions of Sulpicius Gallus, Taurus-Littrow, Hadley Rille, Mare Crisium (craters Picard and Pierce), and NE Mare Fecunditatis. In all these cases these deposits exhibit high Mg/Al ratios which suggest the presence of orange, black, and green pyroclastic glasses. The highest concentration of glasses was inferred in the Sulpicius Gallus Formation at about 35%. The depth of the initial pyroclastic deposits was estimated at 3 to 4 meters. Central Mare Serenitatis exhibits high Mg/Al values but does not possess dark mantle deposits. Orbital Al and Mg/Al data for this region is similar to the very low titanium mare basalts.

  10. Scaling of anomalous Hall effect in Ta/CoFeB/MgAl2O4/Ta multilayers

    NASA Astrophysics Data System (ADS)

    Wu, Yong; Zhang, Qimeng; Meng, Kangkang; Chen, Jikun; Xu, Xiaoguang; Miao, Jun; Jiang, Yong

    2017-06-01

    The anomalous Hall effect (AHE) is studied in Ta/CoFeB/MgAl2O4/Ta multilayers with different thicknesses of MgAl2O4 (t), which causes in-plane magnetic anisotropy (IMA) for t = 1.0 nm and perpendicular magnetic anisotropy (PMA) for t ≥ 1.2 nm. Conventional scaling was demonstrated to be not inadequate in our case. The origin of the AHE in Ta/CoFeB/MgAl2O4/Ta multilayers is mainly an extrinsic mechanism. The contribution of skew scattering (SS) is unneglectable, and both the SS and side jump are enhanced when the magnetic anisotropy changes from IMA to PMA, indicating that the oxidation at the interface of CoFeB/MgAl2O4 has a dominant influence on the AHE.

  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. The development of nontoxic Ag-based brazing alloys

    SciTech Connect

    Timmins, P.F. )

    1994-09-01

    An experimental investigation wad conducted to produce nontoxic, Cd-free brazing alloys that possessed similar melting ranges and mechanical properties to those alloys within the Ag-Cu-Zn-Cd system. The investigation consisted of phase equilibria, Zn equivalence, thermal analysis, extrusion, wire drawing and mechanical testing of alloys based in the Ag-Cu-Zn system. Thermal analysis of these new alloys yielded liquidus temperatures in the range 680 to 775 C (1256--1427 F) and solidus temperatures in the range 625 to 675 C (1157--1247 F). These values compared favorably to the Ag-Cu-Zn-Cd alloys, which have liquidus and solidus temperatures in the ranges of 640 to 710 C (1184--1310 F) and 610 to 620 C (1130--1148 F), respectively, for Ag contents in the 20 to 50 wt-% range. Tensile tests revealed the ultimate tensile strengths of the as-cast Ag-Cu-Zn-Sn alloys to be higher than the toxic Cd-containing alloys of higher Ag content and higher than the ternary Ag-Cu-Zn alloys. For example, the alloy at 35Ag-34Cu-30Zn-1Sn exhibited an as-cast tensile strength of 47.6 kg/mm[sup 2] (67.7 ksi) compared to the alloy at 50Ag-15Cu-16Zn-19Cd with an as-cast tensile strength of 45.7 kg/mm[sup 2] (65 ksi).

  13. Study of solid-solution hardening in binary aluminium-based alloys

    NASA Astrophysics Data System (ADS)

    Draissia, Mohamed; Debili, Mohamed-Yacine

    2005-09-01

    Solid-solution formation in binary aluminium-based alloys is due essentially to the combined effects of the size and valence of solvent and solute atoms, as expected by the four Hume-Rothery rules. The lattice parameter of aluminium in the solid solution of the sputtered Al-Fe films is [Al-a (Å)=4.052-6.6×10-3Y]. The increasing and decreasing evolution of the lattice parameter of copper [Cu-a (Å)=3.612+1.8×10-3Z] and aluminium [Al-a (Å)=4.048-1.6×10-3X] in the sputtered Al-1.8 to 92.5 at. % Cu films is a result of the difference in size between the aluminium and copper atoms. The low solubility of copper in aluminium (<1.8 at % Cu) is due to the valences of solvent and solute atoms in contrast with other sputtered films prepared under similar conditions, such as Al-Mg (20 at. % Mg), Al-Ti (27 at. % Ti), Al-Cr (5at. % Cr) and Al-Fe (5.5 at. % Fe) where the solubility is due to the difference in size.

  14. [Mg/Al layered double hydroxides prepared by microwave-assisted co-precipitation method for the removal of bromate].

    PubMed

    Zhong, Qiong; Li, Huan

    2014-04-01

    In this paper, Mg/Al layered double hydroxides (Mg/Al LDHs) were prepared by the microwave-assisted co-precipitation method and the conventional co-precipitation method. The samples were labeled as Mg/Al LDHs-MW and Mg/Al LDHs-H, respectively. Mg/Al LDHs were characterized by X-ray diffractometer (XRD), Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR). The results showed that the application of microwave in the preparation process promoted the formation of smaller pore diameter and higher crystallinity particles. The pore size and particle size of Mg/Al LDHs-MW were 41.13 nm and 427.08 nm, respectively. Batch experiments were investigated to evaluate the effect of dosage, initial pH and regeneration frequencies for bromate removal. The conclusion showed that the process of bromate removal on Mg/Al LDHs could be described by the pseudo-second kinetic model. The Langmuir isotherm well described the experimental data, and the Mg/Al LDHs-MW has a stronger adsorption capacity while the maximum adsorption capacity (q(0)) of Mg/Al LDHs-MW for bromate was 321.26 microg x g(-1) which was larger than the q(0) (288.74 microg x g(-1)) of Mg/Al LDHs-H. For the continuous fixed-bed column, model simulations using the Thomas model showed that the experimental data obtained at three different columns packed with Mg/Al LDHs-MW were able to predict breakthrough curves. Simulating the maximum adsorption capacity of adsorption column for bromate removal was 288.81 microg x g(-1). When the bed depth was 10 cm, inlet concentration was 800 microg x L(-1) and flow rate was 4.0 mL x min, the correlation coefficient of model was 0.92, indicating that the experimental data was described well by the Thomas model.

  15. 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.

  16. Up-conversion and Photoluminescence in Er3+ Single Crystal MgAl-spinel

    NASA Astrophysics Data System (ADS)

    Mironova-Ulmane, N.; Sarakovskis, A.; Skvortsova, V.

    Traditional and up-conversion luminescence of MgAl2O4 single crystal doped with erbium ions obtained by the Verneuil method has been investigated. The time resolved spectral measurements of the green and red up-conversion luminescence bands show that a build-up part is present in the up-conversion luminescence kinetics. This means that energy transfer process is involved in the creation of the luminescence. Considering rather small concentration of Er3+ in the material (0.12 mass %), the expected up-conversion mechanism should be excited state absorption since the average distance between erbium ions is high. The above-mentioned considerations suggest that clustering of the activator ions is present in the material, which is supported by SEM analysis.

  17. Helium irradiation effects in single crystals of MgAl 2O 4

    NASA Astrophysics Data System (ADS)

    Neeft, E. A. C.; Schram, R. P. C.; van Veen, A.; Labohm, F.; Fedorov, A. V.

    2000-05-01

    Magnesium aluminate spinel, (MgAl2O4), is a promising material as a uranium free matrix for the transmutation of americium. Fission products and α-particles are produced during the transmutation. The impact of α-particles is simulated by 30 keV 3He ion implantations at room temperature (RT) with the doses 6.2, 16, 20 and 53×1015 cm-2. In another set of experiments a single crystal MgAl2O4 (1 0 0) sample is irradiated with α-particles (4.5 MeV) from a 241Am source at RT to a dose of 1.3×1012 cm-2. Helium release from the implanted samples was studied by thermal desorption spectrometry (TDS). The numerical analysis of the experimental thermal desorption results of α-implanted samples to a very low helium concentration (0.0288 appm in the irradiation zone of 12.4 μm) show that helium release is dominated by helium interstitial diffusion with an activation energy of 1.8 eV. In the case of high dose implantation to 1.74 at.% in the implantation zone approximately of 100 nm, helium is released from He-vacancy clusters with the activation energy of 2.35 eV. The evolution of the helium concentration profile in the temperature range from RT to 1483 K is monitored by neutron depth profiling (NDP). It confirms that the release of helium is governed by dissociation from vacancy clusters.

  18. Fabrication of hierarchical core-shell polydopamine@MgAl-LDHs composites for the efficient enrichment of radionuclides

    NASA Astrophysics Data System (ADS)

    Zhu, Kairuo; Lu, Songhua; Gao, Yang; Zhang, Rui; Tan, Xiaoli; Chen, Changlun

    2017-02-01

    Novel hierarchical core/shell structured polydopamine@MgAl-layered double hydroxides (PDA@MgAl-LDHs) composites involving MgAl-layered double hydroxide shells and PDA cores were fabricated thought one-pot coprecipitation assembly and methodically characterized by X-ray diffraction, Fourier transformed infrared spectroscopy, scanning/transmission electron microscopy, selected area electron diffraction, elemental mapping, thermogravimetric analysis and X-ray photoelectron spectroscopy technologies. U(VI) and Eu(III) sorption experiments showed that the PDA@MgAl-LDHs exhibited higher sorption ability with a maximum sorption capacity of 142.86 and 76.02 mg/g at 298 K and pH 4.5, respectively. More importantly, according to XPS analyses, U(VI) and Eu(III) were sorbed on PDA@MgAl-LDHs via oxygen-containing functional groups, and the chemical affinity of U(VI) by oxygen-containing functional groups is higher than that of Eu(III). These observations show great expectations in the enrichment of radionuclides from aquatic environments by PDA@MgAl-LDHs.

  19. Fabrication and spectroscopic properties of Co:MgAl2O4 transparent ceramics by the HIP post-treatment

    NASA Astrophysics Data System (ADS)

    Luo, Wei; Ma, Peng; Xie, Tengfei; Dai, Jiawei; Pan, Yubai; Kou, Huamin; Li, Jiang

    2017-07-01

    Cobalt-doped magnesium aluminate spinel (Co:MgAl2O4) is one of the most important saturable absorbers for the passive Q-switching of solid-state lasers operating at eye-safe wavelength of 1.5 μm. In this work, highly transparent Co:MgAl2O4 ceramics were fabricated by vacuum sintering combined with hot isostatic pressing (HIP) post-treatment, using the mixture of the commercial spinel and the lab-made Co:MgAl2O4 powder as the raw materials. The densification mechanism of Co:MgAl2O4 transparent ceramics was discussed. The microstructure and optical properties of the samples were investigated. The ground state absorption cross section (σGSA) was calculated from the fitted curve of the absorption coefficient spectrum. The results show that Co:MgAl2O4 ceramics fabricated by vacuum sintering at 1500 °C for 5 h and then HIP post-treatment at 1650 °C for 3 h perform good transparency, whose in-line transmittance exceeds 80% at 2500 nm. Moreover, the ground state absorption cross section of 0.02 at.% Co:MgAl2O4 ceramics is calculated to be 3.35 × 10-19 cm2 at the wavelength of 1540 nm, which is promising for the application to the passive Q-switching of solid-state laser operating in the near infrared region (NIR).

  20. Synthesis and energy transfer studies of LaMgAl{sub 11}O{sub 19}:Cr{sup 3+}, Nd{sup 3+} phosphors

    SciTech Connect

    Zhu, Jicheng; Xia, Zhiguo; Liu, Quanlin

    2016-02-15

    Highlights: • Cr{sup 3+}/Nd{sup 3+} co-doped LaMgAl{sub 11}O{sub 19} phosphors were synthesized. • The energy transfer mechanism is ascribed to the dipole–quadrupole interaction. • The materials can convert the UV–vis light into near-infrared emission. - Abstract: Cr{sup 3+}/Nd{sup 3+} co-activated LaMgAl{sub 11}O{sub 19} phosphors have been synthesized by high temperature solid-state method. In the LaMgAl{sub 11}O{sub 19}:Cr{sup 3+}/Nd{sup 3+} system, Cr{sup 3+} can absorb the UV–vis photons (350–650 nm), and then energy transfer takes place between Cr{sup 3+} and Nd{sup 3+}, and finally the samples give near infrared emission originated from Nd{sup 3+}. Energy transfer from Cr{sup 3+} to Nd{sup 3+} is discussed via the variations of the lifetime values of Cr{sup 3+}, and the mechanism has been ascribed to the dipole–quadrupole interaction. The absorption of Cr{sup 3+} in the visible region and the following energy transfer from Cr{sup 3+} to Nd{sup 3+} indicated that the material can potentially serve as spectral convertors to improve the photovoltaic conversion efficiency of silicon-based solar cell.

  1. Incorporation of transition metals into Mg-Al layered double hydroxides: Coprecipitation of cations vs. their pre-complexation with an anionic chelator

    SciTech Connect

    Tsyganok, Andrey; Sayari, Abdelhamid . E-mail: Abdel.Sayari@science.uottawa.ca

    2006-06-15

    A comparative study on two different methods for preparing Mg-Al layered double hydroxides (LDH) containing various divalent transition metals M (M=Co, Ni, Cu) has been carried out. The first (conventional) method involved coprecipitation of divalent metals M(II) with Mg(II) and Al(III) cations using carbonate under basic conditions. The second approach was based on the ability of transition metals to form stable anionic chelates with edta{sup 4-} (edta{sup 4-}=ethylenediaminetetraacetate) that were synthesized and further introduced into LDH by coprecipitation with Mg and Al. The synthesized LDHs were characterized by X-ray diffraction (XRD) and X-ray fluorescence (XRF) methods, thermogravimetry with mass-selective detection of decomposition products (TG-MSD), Fourier transform infrared (FTIR) and Raman spectroscopy techniques. The results obtained were discussed in terms of efficiency of transition metal incorporation into the LDH structure, thermal stability of materials and the ability of metal chelates to intercalate the interlayer space of Mg-Al LDH. Vibrational spectroscopy studies confirmed that the integrity of the metal chelates was preserved upon incorporation into the LDH. - Graphical abstract: Two ways for introducing transition metals M(II) into Mg-Al layered double hydroxides (MY{sup 2-} denotes the edta chelate of transition metal M(II)).0.

  2. Charge compensation assisted enhanced photoluminescence derived from Li-codoped MgAl2O4:Eu3+ nanophosphors for solid state lighting applications.

    PubMed

    Saha, Subhajit; Das, Swati; Ghorai, Uttam Kumar; Mazumder, Nilesh; Gupta, Bipin Kumar; Chattopadhyay, Kalyan Kumar

    2013-09-28

    Highly-luminescent nanophosphors have a decisive role in solid-state lighting (SSL) as well as in field emission display (FED) applications due to their potential use in fabrication of nanophosphor based FED and solid state display devices. Herein, the red emitting highly-luminescent Eu(3+)-Li(+) co-doped magnesium aluminate (MgAl2O4) nanophosphors were synthesized by a customized sol-gel route with an average particle size of 18 nm, which can be easily scaled up in a large quantity. The resulting nanophosphor exhibits hypersensitive red emission, peaking at 615 nm upon 394 nm excitation. Furthermore, comparative photoluminescence (PL) studies have been carried out for Eu(3+) doped and Eu(3+) doped-Li(+) co-doped magnesium aluminate (Li(+) co-doped MgAl2O4:Eu(3+)) nanophosphors, which indicated that Li(+) co-doping significantly improves luminescence intensity along with good crystallinity. Moreover, the charge compensation by addition of Li(+) co-activator in MgAl2O4:Eu(3+) lattice led to the two fold enhancement of PL intensity. The obtained results suggest that this nanophosphor could be an ultimate choice for next generation advanced luminescent nanomaterials for solid state lighting and portable FED devices.

  3. On the cytocompatibility of biodegradable Fe-based alloys.

    PubMed

    Schinhammer, Michael; Gerber, Isabel; Hänzi, Anja C; Uggowitzer, Peter J

    2013-03-01

    Biodegradable iron-based alloys are potential candidates for application as temporary implant material. This study summarizes the design strategy applied in the development of biodegradable Fe-Mn-C-Pd alloys and describes the key factors which make them suitable for medical applications. The study's in vitro cytotoxicity tests using human umbilical vein endothelial cells revealed acceptable cytocompatibility based on the alloys' eluates. An analysis of the eluates revealed that Fe is predominantly bound in insoluble degradation products, whereas a considerable amount of Mn is in solution. The investigation's results are discussed using dose-response curves for the main alloying elements Fe and Mn. They show that it is mainly Mn which limits the cytocompatibility of the alloys. The study also supplies a summary of the alloying elements' influence on metabolic processes. The results and discussion presented are considered important and instructive for future alloy development. The Fe-based alloys developed show an advantageous combination of microstructural, mechanical and biological properties, which makes them interesting as degradable implant material.

  4. Catalytic pyrolysis of natural algae over Mg-Al layered double oxides/ZSM-5 (MgAl-LDO/ZSM-5) for producing bio-oil with low nitrogen content.

    PubMed

    Gao, Lijing; Sun, Jiahui; Xu, Wei; Xiao, Guomin

    2017-02-01

    Cyanobacteria were catalytically pyrolyzed over Mg-Al layered double oxide/ZSM-5 composites (MgAl-LDO/ZSM-5) to produce bio-oil. MgAl-LDO/ZSM-5 with a Mg/Al molar ratio of four was proved to be the best catalyst. Under the optima condition that the final temperature was 823K, heating rate was 10K/min and catalyst/algae mass ratio was 0.75, a maximum yield of liquid (41.1%) was achieved at 823K with a heating rate of 10K/min and a catalyst/algae mass ratio of 0.75, which was much higher than the one obtained without catalyst. The element analysis results proved that this bio-oil had much lower O/C molar ratio and higher HHV. The GC-MS results showed that the bio-oil had less nitrogenous compounds. MgAl4-LDO/ZSM-5 was proved to be an applicable and effective catalyst to obtain bio-oil from catalytic pyrolysis of water-blooming algae.

  5. Tantalum modified ferritic iron base alloys

    NASA Technical Reports Server (NTRS)

    Oldrieve, R. E.; Blankenship, C. P. (Inventor)

    1977-01-01

    Strong ferritic alloys of the Fe-CR-Al type containing 0.4% to 2% tantalum were developed. These alloys have improved fabricability without sacrificing high temperature strength and oxidation resistance in the 800 C (1475 F) to 1040 C (1900 F) range.

  6. MgAl- Layered Double Hydroxide Nanoparticles for controlled release of Salicylate.

    PubMed

    Mondal, Soumini; Dasgupta, Sudip; Maji, Kanchan

    2016-11-01

    Layered double hydroxides (LDHs), have been known for many decades as catalyst and ceramic precursors, traps for anionic pollutants, and additives for polymers. Recently, their successful synthesis on the nanometer scale opened up a whole new field for their application in nanomedicine. Here we report the efficacy of Mg1-xAlx (NO3)x (OH)2 LDH nanoparticles as a carrier and for controlled release of one of the non-steroidal anti-inflammatory drugs (NSAID), sodium salicylate. Mg1-xAlx (NO3)x (OH)2.nH2O nanoparticles were synthesized using co-precipitation method from an aqueous solution of Mg(NO3)2.6H2O and Al(NO3)3.9H2O. Salicylate was intercalated in the interlayer space of Mg-Al LDH after suspending nanoparticles in 0.0025(M) HNO3 and 0.75 (M) NaNO3 solution and using anion exchange method under N2 atmosphere. The shift in the basal planes like (003) and (006) to lower 2θ value in the XRD plot of intercalated sample confirmed the increase in basal spacing in LDH because of intercalation of salicylate into the interlayer space of LDH. FTIR spectroscopy of SA-LDH nano hybrid revealed a red shift in the frequency band of carboxylate group in salicylate indicating an electrostatic interaction between cationic LDH sheet and anionic drug. Differential thermal analysis of LDH-SA nanohybrid indicated higher thermal stability of salicylate in the intercalated form into LDH as compared to its free state. DLS studies showed a particle size distribution between 30-60 nm for pristine LDH whereas salicylate intercalated LDH exhibited a particle size distribution between 40-80nm which is ideal for its efficacy as a superior carrier for drugs and biomolecules. The cumulative release kinetic of salicylate from MgAl-LDH-SA hybrids in phosphate buffer saline (PBS) at pH7.4 showed a sustained release of salicylate up to 72h that closely resembled first order release kinetics through a combination of drug diffusion and dissolution of LDH under physiological conditions. Also the

  7. Surface modification of nickel based alloys for improved oxidation resistance

    SciTech Connect

    Jablonski, Paul D.; Alman, David E.

    2005-02-01

    The present research is aimed at the evaluation of a surface modification treatment to enhance the high temperature stability of nickel-base superalloys. A low Coefficient Thermal Expansion (CTE ~12.5x10-6/°C) alloy based on the composition (in weight %) of Ni-22Mo-12.5Cr was produced by Vacuum Induction Melting and Vacuum Arc Melting and reduced to sheet by conventional thermal-mechanical processing. A surface treatment was devised to enhance the oxidation resistance of the alloys at high temperature. Oxidation tests (in dry and wet air; treated and untreated) were conducted 800°C to evaluate the oxidation resistance of the alloys. The results were compared to the behavior of Haynes 230 (Ni-22Cr) in the treated and untreated conditions. The treatment was not very effective for Haynes 230, as this alloy had similar oxidation behavior in both the treated and untreated conditions. However, the treatment had a significant effect on the behavior of the low CTE alloy. At 800°C, the untreated Ni-12.5Cr alloy was 5 times less oxidation resistant than Haynes 230. However, in the treated condition, the Ni-12.5Cr alloy had comparable oxidation resistance to the Haynes 230 alloy.

  8. Cu/MgAl(2)O(4) as bifunctional catalyst for aldol condensation of 5-hydroxymethylfurfural and selective transfer hydrogenation.

    PubMed

    Pupovac, Kristina; Palkovits, Regina

    2013-11-01

    Copper supported on mesoporous magnesium aluminate has been prepared as noble-metal-free solid catalyst for aldol condensation of 5-hydroxymethylfurfural with acetone, followed by hydrogenation of the aldol condensation products. The investigated mesoporous spinels possess high activity as solid-base catalysts. Magnesium aluminate exhibits superior activity compared to zinc and cobalt-based aluminates, reaching full conversion and up to 81 % yield of the 1:1 aldol product. The high activity can be correlated to a higher concentration of basic surface sites on magnesium aluminate. Applying continuous regeneration, the catalysts can be recycled without loss of activity. Focusing on the subsequent hydrogenation of aldol condensation products, Cu/MgAl2 O4 allows a selective hydrogenation and CO bond cleavage, delivering 3-hydroxybutyl-5-methylfuran as the main product with up to 84 % selectivity avoiding ring saturation. Analysis of the hydrogenation activity reveals that the reaction proceeds in the following order: CC>CO>CO cleavage>ring hydrogenation. Comparable activity and selectivity can be also achieved utilizing 2-propanol as solvent in the transfer hydrogenation, providing the possibility for partial recycling of acetone and optimization of the hydrogen management.

  9. Stable platinum nanoparticles on specific MgAl2O4 spinel facets at high temperatures in oxidizing atmospheres.

    PubMed

    Li, Wei-Zhen; Kovarik, Libor; Mei, Donghai; Liu, Jun; Wang, Yong; Peden, Charles H F

    2013-01-01

    The development of thermally stable, nanometer-sized precious metal-based catalysts remains a daunting challenge. Such materials, especially those based on the use of costly platinum metal, are essential and, to date, non-replaceable for a large number of industrially important catalytic processes. Here we report a well-defined cuboctahedral MgAl2O4 spinel support material that is capable of stabilizing platinum particles in the range of 1-3 nm on its relatively abundant {111} facets during extremely severe aging at 800 °C in air for 1 week. The aged catalysts retain platinum dispersions of 15.9% with catalytic activities for methanol oxidation being ~80% of that of fresh ones, whereas a conventional Pt/γ-Al2O3 catalyst is severely sintered and nearly inactive. We reveal the origin of the markedly superior ability of spinel {111} facets, resulting from strong interactions between spinel surface oxygens and epitaxial platinum {111} facets, inspiring the rational design of anti-sintering supported platinum group catalysts.

  10. Composition-Dependent Reaction Pathways and Hydrogen Storage Properties of LiBH₄/Mg(AlH₄)₂ Composites.

    PubMed

    Pang, Yuepeng; Liu, Yongfeng; Zhang, Xin; Li, Qian; Gao, Mingxia; Pan, Hongge

    2015-11-01

    Herein, an initial attempt to understand the relationships between hydrogen storage properties, reaction pathways, and material compositions in LiBH4-x Mg(AlH4)2 composites is demonstrated. The hydrogen storage properties and the reaction pathways for hydrogen release from LiBH4-x Mg(AlH4)2 composites with x=1/6, 1/4, and 1/2 were systematically investigated. All of the composites exhibit a four-step dehydrogenation event upon heating, but the pathways for hydrogen desorption/absorption are varied with decreasing LiBH4/Mg(AlH4)2 molar ratios. Thermodynamic and kinetic investigations reveal that different x values lead to different enthalpy changes for the third and fourth dehydrogenation steps and varied apparent activation energies for the first, second, and third dehydrogenation steps. Thermodynamic and kinetic destabilization caused by the presence of Mg(AlH4)2 is likely to be responsible for the different hydrogen desorption/absorption performances of the LiBH4-x Mg(AlH4)2 composites.

  11. Stabilization of MgAl2O4 spinel surfaces via doping

    NASA Astrophysics Data System (ADS)

    Hasan, Md. M.; Dholabhai, Pratik P.; Castro, Ricardo H. R.; Uberuaga, Blas P.

    2016-07-01

    Surface structure of complex oxides plays a vital role in processes such as sintering, thin film growth, and catalysis, as well as being a critical factor determining the stability of nanoparticles. Here, we report atomistic calculations of the low-index stoichiometric magnesium aluminate spinel (MgAl2O4) surfaces, each with two different chemical terminations. High temperature annealing was used to explore the potential energy landscape and provide more stable surface structures. We find that the lowest energy surface is {100} while the highest energy surface is {111}. The surfaces were subsequently doped with three trivalent dopants (Y3+, Gd3+, La3+) and one tetravalent dopant (Zr4+) and both the surface segregation energies of the dopants and surface energies of the doped surface were determined. All of the dopants reduce the surface energy of spinel, though this reduction in energy depends on both the size and valence of the dopant. Dopants with larger ionic radius tend to segregate to the surface more strongly and reduce the surface energy to a greater extent. Furthermore, the ionic valence of the dopants seems to have a stronger influence on the segregation than does ionic size. For both undoped and doped spinel, the predicted crystal shape is dominated by {100} surfaces, but the relative fraction of the various surfaces changes with doping due to the unequal changes in energy, which has implications on equilibrium nanoparticle shapes and therefore on applications sensitive to surface properties.

  12. Growth and optical properties of Co,Nd:LaMgAl11O19

    NASA Astrophysics Data System (ADS)

    Xu, Peng; Xia, Changtai; Di, Juqing; Xu, Xiaodong; Sai, Qinglin; Wang, Lulu

    2012-12-01

    Nd,Co:LaMgAl11O19 (abbreviated as Co,Nd:LMA) was grown using the Czochralski method. The structure, polarized absorption spectrum, fluorescence spectrum, and fluorescence decay time were analyzed. The as-grown crystal had very wide absorption bands at 794 nm, which can be pumped by GaAs laser diode without temperature stabilization. Two strong emission bands were present at 1056 nm and 1082 nm with full-width at half-maximum (FWHM) of 6 and 8 nm, respectively. The large FWHM is due to the inhomogeneity of the Nd ion sites. The lifetimes of the 4F3/2 manifold of Co,Nd:LMA at room temperature monitored at 905 nm, 1056 nm, and 1344 nm were 292, 288, and 350 μs, respectively, which was caused by the different contribution of the three different sites with D3h and C2v symmetry. The absorption band of Co is from 1.3 μm to 1.6 μm, and Co,Nd:LMA still has a strong emission around the 1.38 μm, indicating that the Co,Nd:LMA can be applied as a potential self-Q-switched material operating at 1.3 μm.

  13. Quantum-mechanical simulation of MgAl2O4 under high pressure

    NASA Astrophysics Data System (ADS)

    Gracia, L.; Beltrán, A.; Andrés, J.; Franco, R.; Recio, J. M.

    2002-12-01

    The equations of state and phase diagrams of the cubic spinel and two high-pressure polymorphs of MgAl2O4 have been investigated up to 65 GPa using density functional theory, the space-filling polyhedral partition of the unit cell, and the static approximation. Energy-volume curves have been obtained for the spinel phase, the recently observed calcium ferrite-type and calcium titanite-type phases, and the MgO+α-Al2O3 mixture. Zero-pressure unit lengths and compressibilities are well described by the theoretical model, that predicts static bulk moduli about 215 GPa for all the high-pressure forms. Computed equations of state are also in good agreement with the most recent experimental data for all compounds and polymorphs considered. We do not find a continuous pressure-induced phase sequence but the static simulations predict that the oxide mixture, the ferrite phase, and the titanite phase become more stable than the spinel form at 15, 35, and 62 GPa, respectively. A microscopic analysis in terms of polyhedral and bond compressibilities leads to identify the ionic displacements accompanying the phase transformations and to an appealing interpretation of the spinel response to compression.

  14. Stabilization of MgAl2O4 spinel surfaces via doping

    DOE PAGES

    Hasan, Md. M.; Dholabhai, Pratik P.; Castro, Ricardo H. R.; ...

    2016-02-06

    Here, the surface structure of complex oxides plays a vital role in processes such as sintering, thin film growth, and catalysis, as well as being a critical factor determining the stability of nanoparticles. We report atomistic calculations of the low-index stoichiometric magnesium aluminate spinel (MgAl2O4) surfaces, each with two different chemical terminations. High temperature annealing was used to explore the potential energy landscape and provide more stable surface structures. We find that the lowest energy surface is {100} while the highest energy surface is {111}. The surfaces were subsequently doped with three trivalent dopants (Y3+, Gd3+, La3+) and one tetravalentmore » dopant (Zr4+) and both the surface segregation energies of the dopants and surface energies of the doped surface were determined. All of the dopants reduce the surface energy of spinel, though this reduction in energy depends on both the size and valence of the dopant. Dopants with larger ionic radius tend to segregate to the surface more strongly and reduce the surface energy to a greater extent. Furthermore, the ionic valence of the dopants seems to have a stronger influence on the segregation than does ionic size. For both undoped and doped spinel, the predicted crystal shape is dominated by {100} surfaces, but the relative fraction of the various surfaces changes with doping due to the unequal changes in energy, which has implications on equilibrium nanoparticle shapes and therefore on applications sensitive to surface properties.« less

  15. Anisotropic dislocation loop nucleation in ion-irradiated MgAl sub 2 O sub 4

    SciTech Connect

    Zinkle, S.J.

    1991-01-01

    Polycrystalline disks of stoichiometric magnesium aluminate spinel (MgAl{sub 2}O{sub 4}) were irradiated with 2 MeV Al{sup +} ions at 650{degrees}C and subsequently analyzed in cross-section using transmission electron microscopy (TEM). Interstitial dislocation loops were observed on 110 and 11 habit planes. The population of loops on both sets of habit planes was strongly dependent on their orientation with respect to the ion beam direction. The density of loops with habit plane normals nearly perpendicular to the ion beam direction much higher than loops with habit plane normals nearly parallel to the ion beam direction. On the other hand, the loop size was nearly independent of habit plane orientation. This anisotropic loop nucleation does not occur in ion-irradiated metals such as copper. An additional anomaly associated with ion-irradiated spinel is that the loops on 111 planes were partially unfaulted with a Burgers vector of b = a/4<110>. Previous neutron irradiation studies have never reported unfaulted loops in stoichiometric spinel. Possible cause of the unusual response of spinel to ion irradiation are discussed. 12 refs., 14 figs.

  16. Mg, Al, Si, Ca, Ti, Fe, and Ni abundance for a sample of solar analogues

    NASA Astrophysics Data System (ADS)

    López-Valdivia, Ricardo; Bertone, Emanuele; Chávez, Miguel

    2017-05-01

    We report on the determination of chemical abundances of 38 solar analogues, including 11 objects previously identified as super-metal-rich stars. We have measured the equivalent widths for 34 lines of 7 different chemical elements (Mg, Al, Si, Ca, Ti, Fe and Ni) in high-resolution (R ˜ 80 000) spectroscopic images, obtained at the Observatorio Astrofísico Guillermo Haro (Sonora, Mexico), with the Cananea High-resolution Spectrograph. We derived chemical abundances using atlas12 model atmospheres and the Fortran code moog. We confirmed the super-metallicity status of six solar analogues. Within our sample, BD+60 600 is the most metal rich star ([Fe/H] = +0.35 dex), while for HD 166991, we obtained the lowest iron abundance ([Fe/H] = -0.53 dex). We also computed the so-called [Ref] index for 25 of our solar analogues, and we found that BD+60 600 ([Ref] = +0.42) and BD+28 3198 ([Ref] = +0.34) are good targets for exoplanet search.

  17. Pressure-induced Co2+ photoluminescence quenching in MgAl2O4

    NASA Astrophysics Data System (ADS)

    Nataf, Lucie; Rodríguez, Fernando; Valiente, Rafael

    2012-09-01

    This work investigates the electronic structure and photoluminescence (PL) of Co2+-doped MgAl2O4 and their pressure dependence by time-resolved spectroscopy. The variations of the visible absorption band and its associated emission at 663 nm (τ = 130 ns at ambient conditions) with pressure/temperature can be explained on the basis of a configurational energy model. It provides an interpretation for both the electronic structure and the excited-state phenomena yielding photoluminescence emission and the subsequent quenching. We show that there is an excited-state crossover (ESCO) [4T1(P)↔2E(G)] at ambient pressure, which is responsible for the evolution of the emission spectrum from a broadband emission between 300 K and 100 K to a narrow-line emission at lower temperatures. Contrary to expectations from the Tanabe-Sugano diagram, instead of enhancing ESCO phenomena, pressure reduces PL and even suppresses it (PL quenching) above 6 GPa. We explain such variations in terms of pressure-induced nonradiative relaxation to lower excited states: 2E(G)→4T1(F). The variation of PL intensity and its associated lifetime with pressure supports the proposed interpretation.

  18. Mg, Al, Si, Ca, Ti, Fe, and Ni abundance for a sample of solar analogues

    NASA Astrophysics Data System (ADS)

    López-Valdivia, Ricardo; Bertone, Emanuele; Chávez, Miguel

    2017-01-01

    We report on the determination of chemical abundances of 38 solar analogues, including 11 objects previously identified as super metal-rich stars. We have measured the equivalent widths for 34 lines of 7 different chemical elements (Mg, Al, Si, Ca, Ti, Fe, and Ni) in high-resolution (R ˜ 80 000) spectroscopic images, obtained at the Observatorio Astrofísico Guillermo Haro (Sonora, Mexico), with the Cananea High-resolution Spectrograph. We derived chemical abundances using ATLAS12 model atmospheres and the Fortran code MOOG. We confirmed the super metallicity status of 6 solar analogues. Within our sample, BD+60 600 is the most metal-rich star ([Fe/H]=+0.35 dex), while for HD 166991 we obtained the lowest iron abundance ([Fe/H]=-0.53 dex). We also computed the so-called [Ref] index for 25 of our solar analogues, and we found, that BD+60 600 ([Ref]=+0.42) and BD+28 3198 ([Ref]=+0.34) are good targets for exoplanet search.

  19. Rapidly Solidified Oxidation Resistant Niobium Base Alloys

    DTIC Science & Technology

    1992-03-01

    111 Figure 4.33 Cross sectional optical micrographs of Alloy 2 ( Nb-29Ti- 25Cr - 15Mo) after cyclic oxidation at 800’C for 140h. The alloy...179 Figure 5.46 Optical micrographs of specimens for heat treatment 2 following creep for 100 h at a) 650...and slower strain rate on the second attempt, but a useful forging was still not obtained. The composition of Alloy 2 is 31 Nb-29Ti-15Mo- 25Cr . This

  20. Ab initio modeling of decomposition in iron based alloys

    NASA Astrophysics Data System (ADS)

    Gorbatov, O. I.; Gornostyrev, Yu. N.; Korzhavyi, P. A.; Ruban, A. V.

    2016-12-01

    This paper reviews recent progress in the field of ab initio based simulations of structure and properties of Fe-based alloys. We focus on thermodynamics of these alloys, their decomposition kinetics, and microstructure formation taking into account disorder of magnetic moments with temperature. We review modern theoretical tools which allow a consistent description of the electronic structure and energetics of random alloys with local magnetic moments that become totally or partially disordered when temperature increases. This approach gives a basis for an accurate finite-temperature description of alloys by calculating all the relevant contributions to the Gibbs energy from first-principles, including a configurational part as well as terms due to electronic, vibrational, and magnetic excitations. Applications of these theoretical approaches to the calculations of thermodynamics parameters at elevated temperatures (solution energies and effective interatomic interactions) are discussed including atomistic modeling of decomposition/clustering in Fe-based alloys. It provides a solid basis for understanding experimental data and for developing new steels for modern applications. The precipitation in Fe-Cu based alloys, the decomposition in Fe-Cr, and the short-range order formation in iron alloys with s-p elements are considered as examples.

  1. Evaluation of soldered connectors of two base metal ceramic alloys.

    PubMed

    Lima Verde, M A; Stein, R S

    1994-04-01

    Soldered connectors for two base metal ceramic alloys (nickel-chromium and cobalt-chromium) were compared by use of four different techniques: (1) infrared preceramic soldering, (2) gas and oxygen preceramic soldering, (3) porcelain furnace postsoldering under vacuum, and (4) porcelain furnace postsoldering without vacuum. A control group was established with solid cast specimens of each alloy. No statistically significant difference was noted between infrared and torch preceramic soldering techniques for either of the two alloys. However, the joints postsoldered under vacuum were significantly superior to postsoldered connectors without vacuum (p < 0.0001). No significant differences were observed among techniques 1, 2, and 3, although the three groups were substantially superior to technique 4 for both alloys (p = 0.05). The control group for both alloys was appreciably stronger than the soldered groups (p < 0.0001), and the nickel-chromium samples within the control group were significantly stronger than the Co-Cr samples.

  2. Cr{sub 2}Nb-based alloy development

    SciTech Connect

    Liu, C.T.; Tortorelli, P.F.; Horton, J.A.

    1996-08-01

    Alloys of Cr-Cr{sub 2}Nb with exceptionally high strength at 1200{degrees}C have been developed. However, these compositions suffer from limited ductility and toughness at room temperature. Despite improvements from processing modifications, as-fabricated defects still limit room temperature mechanical behavior. In contrast, an alloy system with only a small mismatch of the coefficients of thermal expansion of the two phases, Cr-Cr{sub 2}Zr, showed good fabricability. However, these alloys are weaker than Cr-Cr{sub 2}Nb compositions at high temperatures and have poor oxidation resistance. Silicide coatings can provide high-temperature oxidation and sulfidation protection of these alloys. Improvements in room temperature mechanical properties of Laves-phase-strengthened alloys will rely on further development based on increasing the ductility of the matrix phase by impurity control and compositional modifications.

  3. On the influence of plastic deformation on discontinuous precipitation in Mg-Al

    SciTech Connect

    Duly, D.; Audier, M.; Brechet, Y. . Lab. de Thermodynamique et de Physico-Chimie Metallurgique)

    1993-12-15

    The influence of a prestrain on intragranular precipitation is well known: the dislocations created by plastic deformation act as nucleation sites for heterogeneous precipitation. The influence of a similar prestrain on discontinuous precipitation is much less documented. There appears to be no general rule: depending on the systems considered, the kinetics of discontinuous precipitation can either be accelerated or slowed down. Moreover, in certain alloys, discontinuous precipitation is associated with recrystallization phenomena. In this paper, the authors results on the influence of plastic strain at room temperature on discontinuous precipitation in a Mg-8.5 wt% Al alloy. The interesting feature of this alloy is that plastic deformation induces both dislocation glide and twinning.

  4. First-Principles Thermodynamics Study of Spinel MgAl 2 O 4 Surface Stability

    SciTech Connect

    Cai, Qiuxia; Wang, Jian-guo; Wang, Yong; Mei, Donghai

    2016-09-01

    The surface stability of all possible terminations for three low-index (111, 110, 100) structures of the spinel MgAl2O4 has been studied using first-principles based thermodynamic approach. The surface Gibbs free energy results indicate that the 100_AlO2 termination is the most stable surface structure under ultra-high vacuum at T=1100 K regardless of Al-poor or Al-rich environment. With increasing oxygen pressure, the 111_O2(Al) termination becomes the most stable surface in the Al-rich environment. The oxygen vacancy formation is thermodynamically favorable over the 100_AlO2, 111_O2(Al) and the (111) structure with Mg/O connected terminations. On the basis of surface Gibbs free energies for both perfect and defective surface terminations, the 100_AlO2 and 111_O2(Al) are the most dominant surfaces in Al-rich environment under atmospheric condition. This is also consistent with our previously reported experimental observation. This work was supported by a Laboratory Directed Research and Development (LDRD) project of the Pacific Northwest National Laboratory (PNNL). The computing time was granted by the National Energy Research Scientific Computing Center (NERSC). Part of computing time was also granted by a scientific theme user proposal in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL), which is a U.S. Department of Energy national scientific user facility located at PNNL in Richland, Washington.

  5. Electronic structure of normal, inverse, and partially inverse spinels in the MgAl2O4 system

    NASA Astrophysics Data System (ADS)

    Mo, Shang-Di; Ching, W. Y.

    1996-12-01

    The electronic structure of normal, inverse, and partially inverse spinels in the MgAl2O4 system are studied by means of first-principles calculations. For the normal spinel, the calculated ground-state properties are in good agreement with experimental data. A local-density-approximation band gap of 5.80 eV is obtained. For the inverse and partially inverse spinels, in which up to eight Mg atoms in a tetrahedral coordination are interchanged with eight of the 16 Al atoms in octahedral coordination, the atomic positions are relaxed by realistic interatomic pair potentials. Based on the relaxed models, the electronic structure and their dependence on the inversion parameter λ are studied. The total lattice energy increases as λ increases with a change of slope at λ=4/16. It is found that the general features in the density of states (DOS) in these spinels are quite similar with subtle differences in the peak structures between normal and inverse spinels. The smallest band gap of 4.84 eV is found at λ=4/16. The orbital decomposition of the partial DOS of Al and Mg in different coordination environments is fully analyzed. These results are discussed in the context of an order-disorder phenomenon associated with a cation site interchange, and their implications on spectroscopic detections.

  6. Electrochemical performance of magnesium alloy and its application on the sea water battery.

    PubMed

    Zhao, Hongyang; Bian, Pei; Ju, Dongying

    2009-01-01

    The magnesium sea water battery belongs to a kind of reserved battery, which takes the active metal such as magnesium alloy as the anode based on the sea water as the electrolyte. Experiments of magnesium alloy sea water battery were carried out and its electrochemical performance was studied. Thin sheets of Mg-Al-Zn and Mg-Mn series of magnesium alloy were fabricated and used as the anode of magnesium battery. The discharging voltage and current were measured for different composition and thickness of Mg alloy sheet under various surface state, temperature as well as electrolyte. The effect of the temperature, the surface condition and the electrolyte to the electrical current and voltage were investigated. Anodic dissolution and mechanism of activation of Mg alloy anode were discussed based on surface microstructure observation. The feasibility to apply magnesium alloy sheet to highly effective sea water battery was verified.

  7. Preparation of Ni/Pt catalysts supported on spinel (MgAl 2O 4) for methane reforming

    NASA Astrophysics Data System (ADS)

    Foletto, Edson L.; Alves, Ricardo W.; Jahn, Sérgio L.

    MgAl 2O 4 was synthesized through hydrolysis of metallic alkoxides of Mg 2+ and Al 3+. The formed spinel precursor phase was calcined at temperatures between 600 and 1100 °C, for 4 h. The spinel was utilized as a Ni/Pt catalyst support. The Ni/MgAl 2O 4 catalysts (15% Ni, w/w) containing small amounts of Pt were tested for methane steam reforming. The solids were analyzed by X-ray diffraction (XRD), temperature programmed reduction (TPR) with H 2 and catalytic tests. The spinel phase was formed at temperatures above 700 °C. The addition of small amounts of Pt to Ni/MgAl 2O 4 promoted an increase in surface area. This probably caused the considerable increase in methane conversion.

  8. Synthesis and luminescence of hollow spherical Eu3+- or Tb3+ -doped MgAl2O4 phosphors.

    PubMed

    Wang, Jinghui; Ye, Junwei; Lin, Yuan; Chen, Wendan; Ning, Guiling

    2010-01-01

    Eu3+- or Tb3+ -doped MgAl2O4 hollow spheres have been successfully synthesized via facile hydrothermal method by using carbon spheres as template followed by a subsequent heat treatment. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results showed that the hollow microspheres possessed diameters in the range of 1-2.5 microm and shell thickness of 60-80 nm. A possible formation mechanism for hollow spheres was proposed. MgAl2O4:Eu3+ show strong red emission at 619 nm corresponding to the forced electric dipole (5)D0-->(7)F2 transition of Eu3+, and MgAl2O4:Tb3+ exhibit strong green emission at 545 nm corresponding to 5D4-->(7)F5 transition of Tb3+.

  9. Photophysical properties of donor- N-Ary-Product -acceptor azoic chromophores adsorbed and intercalated into Mg--Al--LDH

    SciTech Connect

    Li, Lei; Liu, Pengfei; Zhang, Li; Chen, Dazhou

    2013-02-15

    Ethyl Orange (EO) and 4-aminoazobenzene-4-sulfonic (AS) anions with Donor- N-Ary-Product -Acceptor structure have been intercalated into the layered double hydroxide (LDH), [Mg{sub 0.66} Al{sub 0.34} (OH){sub 2}] (CO{sub 3}){sub 0.17}{center_dot}0.67H{sub 2}O or adsorbed on the external surface of the host by the method of ion-exchange procedures. The photoabsorption and fluorescence properties of the obtained compounds were different from the pure solid phase of EO and AS. It was suggested that the photophysical properties of guests were closely related to the geometry and electrical structure of the guest molecule, which can affect the distribution and orientation of the guests in the layers or on the surface of the host. The host-guest interactions modulate photophysical properties of guest. In addition, the guest having higher molecular dipole moments surface exchanged on Mg--Al--CO{sub 3}--LDH are beneficial to the enhancement of the blue emission than that of intercalation into LDH. - Graphical abstract: Emission spectra of (a) EO (b) EO surface exchanged on Mg--Al--CO{sub 3}--LDH (c) Mg--Al--EO--LDH. Emission spectra of (a) AS (b) Mg--Al--AS--LDH (c) AS surface exchanged on Mg--Al--CO{sub 3}--LDH. The guests having higher molecular dipole moments surface exchanged on Mg--Al--CO{sub 3}--LDH are beneficial to the enhancement of the blue emission than that of intercalation into LDH. Highlights: Black-Right-Pointing-Pointer EO and AS are intercalated into LDHs or adsorbed on the external surface of LDHs. Black-Right-Pointing-Pointer The host-guest interactions modulate photophysical properties of the guest. Black-Right-Pointing-Pointer The guests having higher molecular dipole moments can enhance the blue emission.

  10. Three-dimensional hierarchical flower-like Mg-Al-layered double hydroxides: highly efficient adsorbents for As(v) and Cr(vi) removal

    NASA Astrophysics Data System (ADS)

    Yu, Xin-Yao; Luo, Tao; Jia, Yong; Xu, Ren-Xia; Gao, Chao; Zhang, Yong-Xing; Liu, Jin-Huai; Huang, Xing-Jiu

    2012-05-01

    3D hierarchical flower-like Mg-Al-layered double hydroxides (Mg-Al-LDHs) were synthesized by a simple solvothermal method in a mixed solution of ethylene glycol (EG) and water. The formation mechanism of the flower-like Mg-Al-LDHs was proposed. After calcination, the flower-like morphology could be completely preserved. With relatively high specific surface areas, Mg-Al-LDHs and calcined Mg-Al-LDHs with 3D hierarchical nanostructures were tested for their application in water purification. When tested as adsorbents in As(v) and Cr(vi) removal, the as-prepared calcined Mg-Al-LDHs showed excellent performance, and the adsorption capacities of calcined Mg-Al-LDHs for As(v) and Cr(vi) were better than those of Mg-Al-LDHs. The adsorption isotherms, kinetics and mechanisms for As(v) and Cr(vi) onto calcined Mg-Al-LDHs were also investigated. The high uptake capability of the as-prepared novel 3D hierarchical calcined Mg-Al-LDHs make it a potentially attractive adsorbent in water purification. Also, this facile strategy may be extended to synthesize other LDHs with 3D hierarchical nanostructures, which may find many other applications due to their novel structural features.3D hierarchical flower-like Mg-Al-layered double hydroxides (Mg-Al-LDHs) were synthesized by a simple solvothermal method in a mixed solution of ethylene glycol (EG) and water. The formation mechanism of the flower-like Mg-Al-LDHs was proposed. After calcination, the flower-like morphology could be completely preserved. With relatively high specific surface areas, Mg-Al-LDHs and calcined Mg-Al-LDHs with 3D hierarchical nanostructures were tested for their application in water purification. When tested as adsorbents in As(v) and Cr(vi) removal, the as-prepared calcined Mg-Al-LDHs showed excellent performance, and the adsorption capacities of calcined Mg-Al-LDHs for As(v) and Cr(vi) were better than those of Mg-Al-LDHs. The adsorption isotherms, kinetics and mechanisms for As(v) and Cr(vi) onto calcined

  11. Fabrication and measurement of optical and spectral properties of the transparent Yb:MgAl2O4 ceramics

    NASA Astrophysics Data System (ADS)

    Balabanov, S. S.; Belyaev, A. V.; Gavrishchuk, E. M.; Mukhin, I. B.; Novikova, A. V.; Palashov, O. V.; Permin, D. A.; Snetkov, I. L.

    2017-09-01

    In this paper results concerning the fabrication of transparent (with 0.1% mol Yb3+), translucent (with 0.5% mol Yb3+) and opaque (up to 5% mol Yb3+) Yb3+: MgAl2O4 ceramics by hot pressing are presented. The alkoxotechnology of starting magnesium aluminate spinel nanopowder synthesis with homogeneous distribution of Yb ions is proposed. The structural properties of the prepared powders and ceramics were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and BET method. The optical transmittance, absorption and emission cross sections, and the upper level lifetime of the Yb3+:MgAl2O4 ceramics were measured.

  12. Exploratory Investigation of Advanced-Temperature Nickel-Base Alloys

    NASA Technical Reports Server (NTRS)

    Freche, John C.; Waters, William J.

    1959-01-01

    An investigation was conducted to provide an advanced-temperature nickel-base alloy with properties suitable for aircraft turbine blades as well as for possible space vehicle applications. An entire series of alloys that do not require vacuum melting techniques and that generally provide good stress-rupture and impact properties was evolved. The basic-alloy composition of 79 percent nickel, 8 percent molybdenum, 6 percent chromium, 6 percent aluminum, and 1 percent zirconium was modified by a series of element additions such as carbon, titanium, and boron, with the nickel content adjusted to account for the additives. Stress-rupture, impact, and swage tests were made with all the alloys. The strongest composition (basic alloy plus 1.5 percent titanium plus 0.125 percent carbon) displayed 384- and 574-hour stress-rupture lives at 1800 F and 15,000 psi in the as-cast and homogenized conditions, respectively. All the alloys investigated demonstrated good impact resistance. Several could not be broken in a low-capacity Izod impact tester and, on this basis, all compared favorably with several high-strength high-temperature alloys. Swaging cracks were encountered with all the alloys. In several cases, however, these cracks were slight and could be detected only by zyglo examination. Some of these compositions may become amenable to hot working on further development. On the basis of the properties indicated, it appears that several of the alloys evolved, particularly the 1.5 percent titanium plus 0.125 percent carbon basic-alloy modification, could be used for advanced- temperature turbine blades, as well as for possible space vehicle applications.

  13. Corrosion evaluation of gold-based dental alloys.

    PubMed

    Corso, P P; German, R M; Simmons, H D

    1985-05-01

    Three commercial gold-based dental alloys and three constant-nobility ternary alloys (Au-Ag-Cu) were evaluated for corrosion using a quantitative test battery. Integration of the current density, in a de-aerated solution of 1% NaCl along the approximate potential range found in the mouth (-300 mV to +300 mV vs. SCE), yields a quantitative rank ordering of the test alloys. The results are combined with prior findings on other commercial alloys to demonstrate the interaction of nobility and microstructure. Nobility determines the overall corrosion resistance for gold-based alloys. However, because of mutual insolubility, alloying with copper induces silver segregation, resulting in a higher corrosion rate at a given nobility. Thus, microstructure has an influence on corrosion, but heat treatments are largely ineffective in altering the basic corrosion characteristics. The test techniques, in combination with tarnish evaluations, provide a quantitative battery for alloy evaluation. The results indicate the combinations of nobility, microstructure, and environment most likely to avoid corrosion difficulties.

  14. Microstructures and oxidation behavior of some Molybdenum based alloys

    SciTech Connect

    Ray, Pratik Kumar

    2011-01-01

    The advent of Ni based superalloys revolutionized the high temperature alloy industry. These materials are capable of operating in extremely harsh environments, comprising of temperatures around 1050 C, under oxidative conditions. Demands for increased fuel efficiency, however, has highlighted the need for materials that can be used under oxidative conditions at temperatures in excess of 1200 C. The Ni based superalloys are restricted to lower temperatures due to the presence of a number of low melting phases that melt in the 1250 - 1450 C, resulting in softening of the alloys above 1000 C. Therefore, recent research directions have been skewed towards exploring and developing newer alloy systems. This thesis comprises a part of such an effort. Techniques for rapid thermodynamic assessments were developed and applied to two different systems - Mo-Si alloys with transition metal substitutions (and this forms the first part of the thesis) and Ni-Al alloys with added components for providing high temperature strength and ductility. A hierarchical approach towards alloy design indicated the Mo-Ni-Al system as a prospective candidate for high temperature applications. Investigations on microstructures and oxidation behavior, under both isothermal and cyclic conditions, of these alloys constitute the second part of this thesis. It was seen that refractory metal systems show a marked microstructure dependence of oxidation.

  15. 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.

  16. METHOD FOR ANNEALING AND ROLLING ZIRCONIUM-BASE ALLOYS

    DOEpatents

    Picklesimer, M.L.

    1959-07-14

    A fabrication procedure is presented for alpha-stabilized zirconium-base alloys, and in particular Zircaloy-2. The alloy is initially worked at a temperature outside the alpha-plus-beta range (810 to 970 deg ), held at a temperature above 970 deg C for 30 minutes and cooled rapidly. The alloy is then cold-worked to reduce the size at least 20% and annealed at a temperature from 700 to 810 deg C. This procedure serves both to prevent the formation of stringers and to provide a randomly oriented crystal structure.

  17. Cladding burst behavior of Fe-based alloys under LOCA

    DOE PAGES

    Terrani, Kurt A.; Dryepondt, Sebastien N.; Pint, Bruce A.; ...

    2015-12-17

    Burst behavior of austenitic and ferritic Fe-based alloy tubes has been examined under a simulated large break loss of coolant accident. Specifically, type 304 stainless steel (304SS) and oxidation resistant FeCrAl tubes were studied alongside Zircaloy-2 and Zircaloy-4 that are considered reference fuel cladding materials. Following the burst test, characterization of the cladding materials was carried out to gain insights regarding the integral burst behavior. Given the widespread availability of a comprehensive set of thermo-mechanical data at elevated temperatures for 304SS, a modeling framework was implemented to simulate the various processes that affect burst behavior in this Fe-based alloy. Themore » most important conclusion is that cladding ballooning due to creep is negligible for Fe-based alloys. Thus, unlike Zr-based alloys, cladding cross-sectional area remains largely unchanged up to the point of burst. Furthermore, for a given rod internal pressure, the temperature onset of burst in Fe-based alloys appears to be simply a function of the alloy's ultimate tensile strength, particularly at high rod internal pressures.« less

  18. Cladding burst behavior of Fe-based alloys under LOCA

    SciTech Connect

    Terrani, Kurt A.; Dryepondt, Sebastien N.; Pint, Bruce A.; Massey, Caleb P.

    2015-12-17

    Burst behavior of austenitic and ferritic Fe-based alloy tubes has been examined under a simulated large break loss of coolant accident. Specifically, type 304 stainless steel (304SS) and oxidation resistant FeCrAl tubes were studied alongside Zircaloy-2 and Zircaloy-4 that are considered reference fuel cladding materials. Following the burst test, characterization of the cladding materials was carried out to gain insights regarding the integral burst behavior. Given the widespread availability of a comprehensive set of thermo-mechanical data at elevated temperatures for 304SS, a modeling framework was implemented to simulate the various processes that affect burst behavior in this Fe-based alloy. The most important conclusion is that cladding ballooning due to creep is negligible for Fe-based alloys. Thus, unlike Zr-based alloys, cladding cross-sectional area remains largely unchanged up to the point of burst. Furthermore, for a given rod internal pressure, the temperature onset of burst in Fe-based alloys appears to be simply a function of the alloy's ultimate tensile strength, particularly at high rod internal pressures.

  19. High dose neutron irradiation of MgAl2O4 spinel: effects of post-irradiation thermal annealing on EPR and optical absorption

    SciTech Connect

    Ibarra, A.; Bravo, D.; Lopez, F J.; Garner, Francis A.

    2005-01-01

    Electron paramagnetic resonance (EPR) and optical absorption spectra were measured during thermal annealing for stoichiometric MgAl2O4 spinel that was previously irradiated in FFTF-MOTA at {approx}405 C to {approx}50 dpa. Both F and F+ centres are to persist up to very high temperatures (over 700C), suggesting the operation of an annealing mechanism based on evaporation from extended defects Using x-ray irradiation following the different annealing steps it was shown that the optical absorption band is related to a sharp EPR band at g=2.0005 and that the defect causing these effects is the F+ centre.

  20. Hydrogen transport in nickel-base alloys

    NASA Astrophysics Data System (ADS)

    Turnbull, A.; Ballinger, R. G.; Hwang, I. S.; Morra, M. M.; Psaila-Dombrowski, M.; Gates, R. M.

    1992-12-01

    The electrochemical permeation technique has been used to characterize hydrogen transport and trapping in pure nickel and in alloys 600, X-750, and 718 at a temperature of 80 °C. The “effective diffusivity ” of hydrogen atoms in alloy 600 is reduced by a factor of about 5 compared to pure nickel. This is attributed to both compositional changes and the presence of [(Ti, Nb)C] carbides. Aging of alloy 600, with subsequent M23C6 carbide precipitation, does not significantly influence the measured “effective diffusivity,” which is explained by the dominant effect of preexisting [(Ti, Nb)C] carbides. The “effective diffusivity” of hydrogen atoms in solution-annealed alloy X-750 is reduced by a factor of about 9 compared to that of pure nickel. This is also attributed to compositional changes and [(Ti,Nb)C] carbides. Aging of alloy X-750, which causes precipitation of γ'[Ni3(Al, Ti)], reduces the “effective diffusivity” by an additional factor of 5 or more. Double aging at 885 °C/24 hours, 704 °C/20 hours following hot working yields the greatest reduction in “effective diffusivity.” Analysis of permeation transients using a diffusion- trapping model indicates a binding energy associated with trapping due to the γ phase of be- tween -31 and -37 kJ/mol. The “effective diffusivity” of hydrogen in alloy 718 is about 40 pct greater than for alloy X-750 for the same double and direct aging treatments. The average “effective diffusivities” of the double-aged and direct-aged alloy 718 are comparable, but the permeation transients for the double-aged treatment are significantly steeper. The double-aged treatment with predominantly δ phase (orthorhombic Ni3Nb) yields a binding energy of about -30 kJ/mol. Analysis of the direct aged-treated 718, which contains predominantly γ″ phase (body-centered tetragonal Ni3Nb) gave a binding energy between -23 and -27 kJ/mol. Seg- regation of hydrogen atoms to the γ matrix interface, combined with a

  1. Amorphous phase formation in mechanically alloyed iron-based systems

    NASA Astrophysics Data System (ADS)

    Sharma, Satyajeet

    Bulk metallic glasses have interesting combination of physical, chemical, mechanical, and magnetic properties which make them attractive for a variety of applications. Consequently there has been a lot of interest in understanding the structure and properties of these materials. More varied applications can be sought if one understands the reasons for glass formation and the methods to control them. The glass-forming ability (GFA) of alloys can be substantially increased by a proper selection of alloying elements and the chemical composition of the alloy. High GFA will enable in obtaining large section thickness of amorphous alloys. Ability to produce glassy alloys in larger section thicknesses enables exploitation of these advanced materials for a variety of different applications. The technique of mechanical alloying (MA) is a powerful non-equilibrium processing technique and is known to produce glassy (or amorphous) alloys in several alloy systems. Metallic amorphous alloys have been produced by MA starting from either blended elemental metal powders or pre-alloyed powders. Subsequently, these amorphous alloy powders could be consolidated to full density in the temperature range between the glass transition and crystallization temperatures, where the amorphous phase has a very low viscosity. This Dissertation focuses on identifying the various Fe-based multicomponent alloy systems that can be amorphized using the MA technique, studying the GFA of alloys with emphasis on improving it, and also on analyzing the effect of extended milling time on the constitution of the amorphous alloy powder produced at earlier times. The Dissertation contains seven chapters, where the lead chapter deals with the background, history and introduction to bulk metallic glasses. The following four chapters are the published/to be published work, where the criterion for predicting glass formation, effect of Niobium addition on glass-forming ability (GFA), lattice contraction on

  2. Damping capacity of TiNi-based shape memory alloys

    NASA Astrophysics Data System (ADS)

    Rong, L. J.; Jiang, H. C.; Liu, S. W.; Zhao, X. Q.

    2007-07-01

    Damping capacity is another primary characteristic of shape memory alloys (SMA) besides shape memory effect and superelasticity. Damping behavior of Ti-riched TiNi SMA, porous TiNi SMA and a novel TiNi/AlSi composite have been investigated using dynamic mechanical analyzer (DMA) in this investigation. All these alloys are in martensitic state at room temperature and thus possess the high potential application value. Ti 50.2Ni 49.8 SMA has better damping capacity in pure martensitic state and phase transformation region due to the motion of martensite twin interface. As a kind of promising material for effective dampers and shock absorbing devices, porous TiNi SMA can exhibit higher damping capacity than the dense one due to the existence of the three-dimensioned connecting pore structure. It is found that the internal friction of porous TiNi SMA mainly originates from microplastic deformation and mobility of martensite interface and increases with the increase of the porosity. A novel TiNi/AlSi composite has been developed successfully by infiltrating AlSi alloy into the open pores of porous TiNi alloy with 60% porosity through compression casting. It shows the same phase transformation characteristics as the porous TiNi alloy. The damping capacity of the composite has been increased and the compressive strength has been also promoted remarkably. Suggestions for developing higher damping alloys based on TiNi shape memory alloy are proposed in this paper.

  3. Defect Band Characteristics in Mg-Al and Al-Si High-Pressure Die Castings

    NASA Astrophysics Data System (ADS)

    Gourlay, C. M.; Laukli, H. I.; Dahle, A. K.

    2007-08-01

    Bands of positive macrosegregation and porosity commonly follow the surface contour of components produced by high-pressure die casting (HPDC). In this article, Al alloy AlSi7Mg and Mg alloys AZ91 and AM60 were cast into tensile test bars using cold-chamber (cc) HPDC. Microstructural characterization revealed that externally solidified crystals (ESCs) are not necessary for defect band formation, and that defect bands can form both near to and relatively far from any surface layer of different microstructure. The defect bands were 140 to 240 μm thick. In addition to defect-band-related macrosegregation, the castings also contained inverse segregation and surface segregation. Defect bands are shown to have the characteristics of the dilatant shear bands reported in past rheology studies, indicating that defect bands form due to strain localization in partially solid material during the HPDC process.

  4. Directionally solidified iron-base eutectic alloys

    NASA Technical Reports Server (NTRS)

    Tewari, S. N.

    1976-01-01

    Pseudobinary eutectic alloys with nominal compositions of Fe-25Ta-22Ni-10Cr and Fe-15.5Nb-14.5Ni-6.0Cr were directionally solidified at 0.5 centimeter per hour. Their microstructure consisted of the fcc, iron solid-solution, matrix phase reinforced by about 41-volume-percent, hcp, faceted Fe2Ta fibers and 41-volume-percent, hcp, Fe2Nb lamellae for the tantalum- and niobium-containing alloys, respectively. The microstructural stability under thermal cycling and the temperature dependence of tensile properties were investigated. These alloys showed low elevated-temperature strength and were not considered suitable for application in aircraft-gas-turbine blades although they may have applicability as vane materials.

  5. Fe-based long range ordered alloys

    DOEpatents

    Liu, Chain T; Inouye, Henry; Schaffhauser, Anthony C.

    1980-01-01

    Malleable long range ordered alloys having high critical ordering temperatures exist in the V(Co,Fe).sub.3 and V(Co,Fe,Ni).sub.3 system having the composition comprising by weight 22-23% V, 35-50% Fe, 0-22% Co and 19-40% Ni with an electron density no greater than 8.00. Excellent high temperature properties occur in alloys having compositions comprising by weight 22-23% V, 35-45% Fe, 0-10% Co, 25-35% Ni; 22-23% V, 28-33% Ni and the remainder Fe; and 22-23% V, 19-22% Ni, 19-22% Co and the remainder Fe. The alloys are fabricable by casting, deforming and annealing for sufficient time to provide ordered structure.

  6. Fe-based long range ordered alloys

    DOEpatents

    Liu, C.T.

    Malleable long range ordered alloys with high critical ordering temperatures exist in the V(Co,Fe)/sub 3/ and V(Co,Fe,Ni)/sub 3/ system. The composition comprising by weight 22 to 23% V, 35 to 50% Fe, 0 to 22% Co and 19 to 40% Ni with an electron density no greater than 8.00. Excellent high temperature properties occur in alloys having compositions comprising by weight 22 to 23% V, 35 to 45% Fe, 0 to 10% Co, 25 to 35% Ni; 22 to 23% V, 28 to 33% Ni and the remainder Fe; and 22 to 23% V, 19 to 22% Co and the remainder Fe. The alloys are fabricable by casting, deforming and annealing for sufficient time to provide ordered structure.

  7. Fabrication of tungsten wire reinforced nickel-base alloy composites

    NASA Technical Reports Server (NTRS)

    Brentnall, W. D.; Toth, I. J.

    1974-01-01

    Fabrication methods for tungsten fiber reinforced nickel-base superalloy composites were investigated. Three matrix alloys in pre-alloyed powder or rolled sheet form were evaluated in terms of fabricability into composite monotape and multi-ply forms. The utility of monotapes for fabricating more complex shapes was demonstrated. Preliminary 1093C (2000F) stress rupture tests indicated that efficient utilization of fiber strength was achieved in composites fabricated by diffusion bonding processes. The fabrication of thermal fatigue specimens is also described.

  8. The metallography of a nickel base casting alloy.

    PubMed

    Lewis, A J

    1975-10-01

    Three groups of tensile test pieces were produced using a nickel base partial denture casting alloy and employing induction fusion in each case. The first group was produced fro new metal, the second from metal which had been recast four times, and the third from new overheated metal. Samples of alloy were cut from each group, and together with a piece from an original ingot, were mounted, polished, etched, and examined under a metallurgical microscope.

  9. Enhancement of the hydrogen storage capacity of Mg(AlH4)2 by excess electrons: a DFT study.

    PubMed

    Kang, Sunwoo; Karthikeyan, S; Lee, Jin Yong

    2013-01-28

    The enhancement of hydrogen storage in complexes of magnesium alanate ([Mg(AlH(4))(2)](n)(-) where n = 2, 3) and their anions was investigated using the B3LYP/6-311++G** method. Hydrogen atoms were chemically absorbed on [Mg(AlH(4))(2)](n)(-) (n = 2, 3) with binding energies of -83 to -91.23 kcal mol(-1). It was determined that a maximum of two hydrogen atoms can be absorbed on [Mg(AlH(4))(2)](n)(-) (n = 2, 3) complexes at 10.51 and 10.21 wt%, respectively. Natural bond order analysis revealed that, in the absence of hydrogen, the excess electron population lies predominantly along the sigma bonds between Mg(2+) atoms, while, upon absorption of the hydrogen atoms, the excess electron population lies on the absorbed hydrogen atoms. The vertical detachment energy showed that the excess electron is strongly bound to [Mg(AlH(4))(2)](n)(-) (n = 2, 3) complexes with energies of 78 to 153 kcal mol(-1). It can be seen from the stabilization energy values that the stability of hydrogen-absorbed complexes with excess electrons was significantly enhanced.

  10. Monolithic thermally bonded Er3+, Yb3+:glass/Co2+:MgAl2O4 microchip lasers

    NASA Astrophysics Data System (ADS)

    Mlynczak, Jaroslaw; Belghachem, Nabil

    2015-12-01

    The highest ever reported 10 kW peak power in monolithic thermally bonded Er3+, Yb3+:glass/Co2+:MgAl2O4 microchip laser was achieved. To show the superiority of monolithic microchip lasers over those with external mirrors the laser generation characteristics of the same samples in both cases were compared.

  11. Improved Toughness Alloys Based on Titanium Aluminides

    DTIC Science & Technology

    1989-10-26

    2Sn-4Zr2Mo and creep rupture =to inconel 718). 6C AVIAGIE 20 -- ALLOYS Am VERAGE FOR to 400 O’)ALLOYS 20 x" T, 20kl- I Oft3V 1 46 T1. IF 110 kb 3V O0MQ...I~j 00 00 I 0 0 (A 30 ) C L 0 o ( 0(D D ( - r_ 00 . C-0. -n r- r- Cfr -H - CD 1- LO t Ne4) C) 00U’ L S..)~O 0c% 0~~ o~~r 𔃺 C,4 0 - - . o. I I - LAC. 0

  12. Nanotwins in Nanocrystalline Mg-Al Alloys: An Insight from High-Resolution TEM and Molecular Dynamics Simulation

    DTIC Science & Technology

    2013-09-25

    While such behavior has been observed for fcc and bcc materials, deformation twins are rarely observed in hcp nc Mg [2]. It has been reported that...size to the nanometer scale [3–5]. More explicitly, in hcp metals, dislocations on the non-close-packed pyramidal planes are much harder to be...U C L A )] a t 1 9: 57 0 5 O ct ob er 2 01 3 grained hcp metals when loaded [8–10]. These deformation twins, which provide the dominant

  13. Salt Fog Testing Iron-Based Amorphous Alloys

    SciTech Connect

    Rebak, Raul B.; Aprigliano, Louis F.; Day, S. Daniel; Farmer, Joseph C.

    2007-07-01

    Iron-based amorphous alloys are hard and highly corrosion resistant, which make them desirable for salt water and other applications. These alloys can be produced as powder and can be deposited as coatings on any surface that needs to be protected from the environment. It was of interest to examine the behavior of these amorphous alloys in the standard salt-fog testing ASTM B 117. Three different amorphous coating compositions were deposited on 316L SS coupons and exposed for many cycles of the salt fog test. Other common engineering alloys such as 1018 carbon steel, 316L SS and Hastelloy C-22 were also tested together with the amorphous coatings. Results show that amorphous coatings are resistant to rusting in salt fog. Partial devitrification may be responsible for isolated rust spots in one of the coatings. (authors)

  14. Ductile superconducting copper-base alloys.

    PubMed

    Tsuei, C C

    1973-04-06

    A new class of ductile superconductors has been prepared by casting and appropriate heat treatments. These alloys superconduct between 4 degrees and 18 degrees K and contain at least 90 atom percent copper and a superconducting phase such as Nb(3)Sn or niobium. They can be processed into wires by conventional metallurgical techniques.

  15. Schaeffler-Type Phase Diagram of Ti-Based Alloys

    NASA Astrophysics Data System (ADS)

    Ishida, K.

    2017-07-01

    The α(hcp)/β(bcc) phase equilibria of Ti-based multi-component alloys can be described by a Schaeffler-type diagram, where Al and Mo equivalents (Aleq and Moeq) are used. Aleq is thermodynamically defined by the ratio of partial molar free energy changes transfer of one mole of each α forming element and Al from a dilute solution of α to β phases, while Moeq is also deduced by similar thermodynamic quantities of β forming element and Mo. Aleq and Moeq for 40 alloying elements are estimated from the thermodynamic parameters assessed by Kaufman and Murray. It is shown that three types of Ti alloys, i.e., α and near α, α+β, and β alloys, can be exactly classified using Aleq and Moeq. The Ms and β transus temperatures can also be predicted by Aleq and Moeq. The proposed Aleq and Moeq are very useful for alloy design, heat treatment, and microstructural evolution of Ti-based alloys.

  16. Schaeffler-Type Phase Diagram of Ti-Based Alloys

    NASA Astrophysics Data System (ADS)

    Ishida, K.

    2017-10-01

    The α(hcp)/β(bcc) phase equilibria of Ti-based multi-component alloys can be described by a Schaeffler-type diagram, where Al and Mo equivalents (Aleq and Moeq) are used. Aleq is thermodynamically defined by the ratio of partial molar free energy changes transfer of one mole of each α forming element and Al from a dilute solution of α to β phases, while Moeq is also deduced by similar thermodynamic quantities of β forming element and Mo. Aleq and Moeq for 40 alloying elements are estimated from the thermodynamic parameters assessed by Kaufman and Murray. It is shown that three types of Ti alloys, i.e., α and near α, α+β, and β alloys, can be exactly classified using Aleq and Moeq. The Ms and β transus temperatures can also be predicted by Aleq and Moeq. The proposed Aleq and Moeq are very useful for alloy design, heat treatment, and microstructural evolution of Ti-based alloys.

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

    SciTech Connect

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

    2013-02-15

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

  18. The resistance of selected high strength alloys to embrittlement by a hydrogen environment. [iron and cobalt base alloys

    NASA Technical Reports Server (NTRS)

    Benson, R. B., Jr.

    1974-01-01

    Selected high strength iron base and cobalt base alloys were resistant to degradation of mechanical properties in a one atmosphere hydrogen environment at ambient temperature. These alloys were strengthened initially by cold working which produced strain induced martensite and fcc mechanical twins in an fcc matrix. Heat treatment of the cobalt base alloy after cold working produced carbide precipitates with retention of an hcp epsilon phase which increased the yield strength level. High strength alloys can be produced which have some resistance to degradation of mechanical properties by a hydrogen environment under certain conditions.

  19. Study on hemocompatibility and corrosion behavior of ion implanted TiNi shape memory alloy and Co-based alloys.

    PubMed

    Liang, Chenghao; Huang, Naibao

    2007-10-01

    Biomedical TiNi shape memory alloy and Co-based alloys were ion implanted, and corrosion resistance and hemocompatibility of these had been investigated with electrochemical method, dynamic clotting time, and hemolysis rate tests. The results indicated that the electrochemical stability and anodic polarization behavior of the materials were improved significantly after ion implantation. When TiNi, Co-based alloys were implanted Mo + C and Ti + C, respectively, the corrosion potentials were enhanced more than 200 mV, passive current densities decreased, and passive ranges were broadened. Dynamic clotting time of the ion implanted substances was prolonged and hemolysis rate decreased. All the results pointed out that corrosion resistance and hemocompatibility of the alloys were improved by ion implantation, and effects of dual implantation was better than that of C single implantation. X-ray diffraction analysis of the alloys after dual implantation revealed that TiC, Mo(2)C, Mo(9)Ti(4), and Mo appeared on the surface of TiNi alloy, and CoC(x), Co(3)Ti, TiC, and TiO on the surface of Co-based alloys. These phases dispersing on the alloy surface formed amorphous film, prevented dissolving of alloy elements and improved the corrosion resistance and hemocompatibility of the alloys.

  20. Iron and iron-based alloys for temporary cardiovascular applications.

    PubMed

    Francis, A; Yang, Y; Virtanen, S; Boccaccini, A R

    2015-03-01

    In the last decade, biodegradable metals have emerged as a topic of interest for particular biomedical applications which require high strength to bulk ratio, including for cardiovascular stents. The advantages of biodegradable materials are related to the reduction of long term risks associated with the presence of permanent metal implants, e.g. chronic inflammation and in-stent restenosis. From a structural point of view, the analysis of the literature reveals that iron-based alloys used as temporary biodegradable stents have several advantages over Mg-based alloys in terms of ductility and strength. Efforts on the modification and tunability of iron-based alloys design and compositions have been mainly focused on controlling the degradation rate while retaining the mechanical integrity within a reasonable period. The early pre-clinical results of many iron-based alloys seem promising for future implants developments. This review discusses the available literature focusing mainly on: (i) Fe and Fe-based alloys design and fabrication techniques; (ii) in vitro and in vivo performance; (iii) cytotoxicity and cell viability tests.

  1. Glass-ceramics with Co2+:Mg(Al,Ga)2O4 nanocrystals: novel saturable absorber for compact erbium lasers

    NASA Astrophysics Data System (ADS)

    Loiko, Pavel; Vitkin, Vladimir; Dymshits, Olga; Zhilin, Alexander; Alekseeva, Irina; Skoptsov, Nikolai; Malyarevich, Alexander; Mateos, Xavier; Yumashev, Konstantin

    2017-02-01

    We report on the passive Q-switching of a compact diode-side-pumped Er,Yb:glass laser by a novel saturable absorber (SA) based on transparent glass-ceramics (GC) containing Co2+Mg(Al,Ga)2O4 nanocrystals. To prepare the GC, an initial magnesium aluminosilicate glass doped with Ga2O3 containing 0.1 mol% CoO was synthesized by a conventional melt-quenching technique and heat-treated at 850-950 °C. The X-ray diffraction analysis of the GC confirmed the precipitation of Co2+Mg(Al,Ga)2O4 crystals with spinel structure (6-7 nm in size). Depending on the heat-treatment temperature, the saturation intensity for the GC measured at 1540 nm was in the 0.5...0.7 J/cm2 range and the recovery time was in the 240...335 ns range. Using the SA based on GC prepared by the heat-treatment at 950 °C with an initial transmission of 84.7%, we generated stable Q-switched pulses 1.14 mJ in energy and 7.2 ns in duration. The peak power reached 160 kW, the repetition rate was 1 Hz and the laser wavelength was 1535 nm. The developed GCs are promising for Q-switching of erbium lasers emitting at 1.5-1.7 μm.

  2. Stress Corrosion Cracking and Oxidation Characteristics of Boride-Strengthend Microcrystalline Iron and Nickel Based Alloys.

    DTIC Science & Technology

    1984-10-22

    through subsequent thermomechanical treatments make this class of alloy attractive for many applications. One such relatively new class of alloys based...crystallizing it in the solid state) using controlled thermal or thermomechanical treatments. Preliminary evaluations of the Fe, Ni, and Co-based micrystalline...and iron in alloys 3 and 4). Each of the four microcrystalline alloys was processed in similar ways. Each alloy was induction melted and chill block

  3. The effect of aluminium on the metallography of a nickel base removable partial denture casting alloy.

    PubMed

    Lewis, A J

    1978-12-01

    Three special nickel-chromium alloys were prepared in which the aluminum levels were adjusted both above and below that of a commercial nickel base dental casting alloy. Tensile and metallographic evaluation of representative samples of the alloys were made and the changes in the properties of the alloys are reported.

  4. In situ synthesis of poly(methyl methacrylate)/MgAl layered double hydroxide nanocomposite with high transparency and enhanced thermal properties

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Feng, Li; Qu, Baojun

    2004-04-01

    A novel poly(methyl methacrylate)/MgAl layered double hydroxide (LDH) nanocomposite (PMMA-MgAl NC) with high transparency and enhanced thermal properties was synthesized in situ by adding sodium hydroxide aqueous solution to an emulsion consisting of metal ion aqueous solution, sodium dodecyl sulfate, methyl methacrylate, and benzoyl peroxide, then followed by the thermal initiation polymerization. The basal spacing of PMMA-MgAl NC was 2.72 nm determined by X-ray diffraction measurement. The intercalated MgAl LDH particles of 60-120 nm width and 25-40 nm thickness were well dispersed at molecular level in the PMMA matrix. When the 50% weight loss was selected as a comparison point, the decomposition temperature of PMMA-MgAl NC sample with 30 wt% MgAl LDH (including dodecyl sulfate) was ca. 45 °C higher than that of pure PMMA.

  5. DEVELOPMENT OF PROTECTIVE COATINGS FOR TANTALUM-BASE ALLOYS

    DTIC Science & Technology

    PHASE STUDIES, PHYSICAL PROPERTIES, REFRACTORY MATERIALS, SILICIDES , SILICON COATINGS , SILICON COMPOUNDS, TANTALUM, TENSILE PROPERTIES, TITANIUM COMPOUNDS, TUNGSTEN ALLOYS, VANADIUM ALLOYS, VAPOR PLATING, ZINC COATINGS ....TANTALUM ALLOYS, ALLOYS, ALUMINUM COATINGS , ALUMINUM COMPOUNDS, BORON COMPOUNDS, CERAMIC COATINGS , CHROMIUM COMPOUNDS, COATINGS , FLAME SPRAYING...HAFNIUM ALLOYS, HAFNIUM COMPOUNDS, HARDNESS, HEAT RESISTANT ALLOYS, INTERMETALLIC COMPOUNDS, METAMATHEMATICS, NIOBIUM ALLOYS, OSCILLOGRAPHS, OXIDES

  6. 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

  7. 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.

  8. 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.

  9. Applications of selenium-based alloys for digital radiography

    NASA Astrophysics Data System (ADS)

    L'Ecuyer, J.; Mouton, A.; Legros, A.; Selmani, A.; Currie, J.; Degtorov, S.

    Selenium is presently considered for radiographic applications in medical imaging and non-destructive testing. Conventional detection techniques include scintillators, storage phosphors and direct converters for which selenium-based alloys are ideally suited. Fabrication techniques for detector based on selenium involve large-scale coating operations resulting in the production of amorphous layers several hundred microns thick. The chemistry and structural properties of these layers are instrumental in the performance of the detectors. We will describe the thermodynamic properties of selenium-based alloys and show that the level of dissociation of the alloy during the coating operation is determined by the nature of the vapor species present. High detector performance can only be obtained by minimizing the amount of dissociation and by preventing crystallization of the film.

  10. Preparation of a novel Ni/Co-based alloy gradient coating on surface of the crystallizer copper alloy by laser

    NASA Astrophysics Data System (ADS)

    Chen, Suiyuan; Liang, Jing; Liu, Changsheng; Sun, Kai; Mazumder, Jyoti

    2011-12-01

    A high wear-resistant gradient coating made of Ni/Co-based alloys on the surface of a Cu alloy substrate was synthesized using a YAG laser induced in situ reaction method. The coating consists of three layers: the first is a Ni-based alloy layer, the second and third are Co-based alloy layers. The microhardness increases gradually from 98 HV in the Cu alloy substrate to the highest level of 876 HV in the third layer. The main phase of the Co-based alloy layer is CoCr2(Ni,O)4, coexisting with the Fe13Mo2B5, Cr(Co(Mo, and FeCr0.29Ni0.16C0.06 phases. Wear tests indicate that the gradient coating has good bond strength and wear properties with a wear coefficient of 0.31 (0.50 for the Cu alloy substrate). Also, the wear loss of the coating is only 0.01 g after it has been abraded for 60 min, which is only one fifth of that of the Cu alloy of the crystallizer. Wear tests of the gradient coating reveal good adhesive friction and wear properties when sliding against steel under dry conditions. This novel technique may have good application to make an advanced coating on the surface of the Cu alloy crystallizer in a continuous casting process.

  11. On BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphor degradation mechanism by vacuum-ultraviolet excitation

    SciTech Connect

    Bizarri, G.; Moine, B.

    2005-12-01

    Additional to a correct color and a high efficiency, phosphors for plasma display panels must maintain their light output for thousands of hours. Often the degradation is the restricting factor in using phosphors. In this article, the mechanism of luminance decrease in blue-emitting BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphor during the operation of the PDPs has been studied. It is shown experimentally that the aging process is mainly due to the vacuum-ultraviolet excitation (VUV). It is demonstrated that the degradation mechanism can be accelerated by using a 193 nm laser excitation. Based on excitation, reflectance, thermoluminescence spectra, and aging or annealing processes by laser excitation, the main causes of the degradation are demonstrated. The aging process can be separated in two different processes according to the temperature: a first one, at low temperature, corresponding to the autoionization of luminescent centers (Eu{sup 2+}{yields}Eu{sup 3+}); and a second one, at high temperature, linked to the formation of traps in the phosphor. These traps induce a perturbation of the energy migration in the phosphor. In addition, the relevant parameters of trap formation are highlighted: density of the VUV excitation, temperature, and atmosphere/pressure surrounding the phosphor. A model of BaMgAl{sub 10}O{sub 17}:Eu{sup 2+} phosphor degradation mechanism is proposed.

  12. Anion exchange reaction potentials as approximate estimates of the relative thermodynamic stabilities of Mg/Al layered double hydroxides containing different anions.

    PubMed

    Prasad, Belavalli E; Kamath, P Vishnu; Vijayamohanan, K

    2011-11-15

    Coatings of hydrotalcite-like nitrate-intercalated Mg/Al layered double hydroxides are electrochemically deposited on a Pt electrode by electrogeneration of base by reduction of a mixed metal nitrate aqueous solution. As-prepared coatings are stable to workup and function as rugged electrodes. The voltammetric response generated by anion exchange of intercalated nitrate for dissolved anions from solution under equilibrium conditions is employed to estimate the thermodynamic stabilities of the Mg/Al layered double hydroxides comprising different anions relative to the nitrate-containing phase. Among monovalent anions, the most stable is the fluoride-containing LDH (ΔG° = -48.7 kJ mol(-1)) relative to the nitrate-containing LDH. The stability in aqueous phase decreases as F(-) > Cl(-) > Br(-) > NO(2)(-) > NO(3)(-), whereas, among divalent anions, SO(4)(2-) (ΔG° = -8.7 kJ mol(-1)) > CO(3)(2-) (ΔG° = 14.3 kJ mol(-1)). The results of monovalent ions match well with the Miyata series, whereas the divalent anion series is at variance with the commonly held belief that carbonate-LDHs are more stable than sulfate-LDHs.

  13. Non-contact atomic force microscopy study of hydroxyl groups on the spinel MgAl2O4(100) surface.

    PubMed

    Federici Canova, F; Foster, A S; Rasmussen, M K; Meinander, K; Besenbacher, F; Lauritsen, J V

    2012-08-17

    Atom-resolved non-contact atomic force microscopy (NC-AFM) studies of the magnesium aluminate (MgAl(2)O(4)) surface have revealed that, contrary to expectations, the (100) surface is terminated by an aluminum and oxygen layer. Theoretical studies have suggested that hydrogen plays a strong role in stabilizing this surface through the formation of surface hydroxyl groups, but the previous studies did not discuss in depth the possible H configurations, the diffusion behaviour of hydrogen atoms and how the signature of adsorbed H is reflected in atom-resolved NC-AFM images. In this work, we combine first principles calculations with simulated and experimental NC-AFM images to investigate the role of hydrogen on the MgAl(2)O(4)(100) surface. By means of surface energy calculations based on density functional theory, we show that the presence of hydrogen adsorbed on the surface as hydroxyl groups is strongly predicted by surface stability considerations at all relevant partial pressures of H(2) and O(2). We then address the question of how such adsorbed hydrogen atoms are reflected in simulated NC-AFM images for the most stable surface hydroxyl groups, and compare with experimental atom-resolved NC-AFM data. In the appendices we provide details of the methods used to simulate NC-AFM using first principles methods and a virtual AFM.

  14. Durable pd-based alloy and hydrogen generation membrane thereof

    DOEpatents

    Benn, Raymond C.; Opalka, Susanne M.; Vanderspurt, Thomas Henry

    2010-02-02

    A durable Pd-based alloy is used for a H.sub.2-selective membrane in a hydrogen generator, as in the fuel processor of a fuel cell plant. The Pd-based alloy includes Cu as a binary element, and further includes "X", where "X" comprises at least one metal from group "M" that is BCC and acts to stabilize the .beta. BCC phase for stability during operating temperatures. The metal from group "M" is selected from the group consisting of Fe, Cr, Nb, Ta, V, Mo, and W, with Nb and Ta being most preferred. "X" may further comprise at least one metal from a group "N" that is non-BCC, preferably FCC, that enhances other properties of the membrane, such as ductility. The metal from group "N" is selected from the group consisting of Ag, Au, Re, Ru, Rh, Y, Ce, Ni, Ir, Pt, Co, La and In. The at. % of Pd in the binary Pd--Cu alloy ranges from about 35 at. % to about 55 at. %, and the at. % of "X" in the higher order alloy, based on said binary alloy, is in the range of about 1 at. % to about 15 at. %. The metals are selected according to a novel process.

  15. Several Issues in the Development of Ti-Nb-Based Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Kim, Hee Young; Miyazaki, Shuichi

    2016-12-01

    Ni-free Ti-based shape memory alloys, particularly Ti-Nb-based alloys, have attracted increasing attraction since the early 2000s due to their wide application potentials in biomedical fields. Recently, there has been significant progress in understanding the martensitic transformation behavior of Ti-Nb-based alloys and many novel superelastic alloys have been developed. The superelastic properties of Ti-Nb-based alloys have been remarkably improved through the optimization of alloying elements and microstructure control. In this paper, in order to explore and establish the alloy design strategy, several important issues in the development of Ti-Nb-based shape memory alloys are reviewed. Particularly, the effects of alloying elements on the martensitic transformation temperature and the transformation strain are analyzed. The effects of omega phase and texture on the superelastic properties are also discussed.

  16. Yield Strength of Transparent MgAl2O4 Nano-Ceramic at High Pressure and Temperature.

    PubMed

    Zhang, Jie; Lu, Tiecheng; Chang, Xianghui; Jiang, Shengli; Wei, Nian; Qi, Jianqi

    2010-05-23

    We report here experimental results of yield strength and stress relaxation measurements of transparent MgAl2O4 nano-ceramics at high pressure and temperature. During compression at ambient temperature, the differential strain deduced from peak broadening increased significantly with pressure up to 2 GPa, with no clear indication of strain saturation. However, by then, warming the sample above 400°C under 4 GPa, stress relaxation was obviously observed, and all subsequent plastic deformation cycles are characterized again by peak broadening. Our results reveal a remarkable reduction in yield strength as the sintering temperature increases from 400 to 900°C. The low temperature for the onset of stress relaxation has attracted attention regarding the performance of transparent MgAl2O4 nano-ceramics as an engineering material.

  17. Preparation and spectroscopy characterization of Eu:MgAl2O4 nanopowder prepared by modified Pechini method.

    PubMed

    Wiglusz, R J; Grzyb, T; Lis, S; Strek, W

    2009-10-01

    In the present work, a modified Pechini method was employed to prepare nanostructured MgAl2O4 spinel powders doped with Eu3+ ions. The XRD analyses demonstrated that the powders were single-phase spinel nanopowders with high crystallite dispersion. The average spinel particle size was determined to be approximately 15 nm for calcination at 700 degrees C, and approximately 20 at 1000 degrees C. The emission and excitation spectra measured for the samples calcinated at 700 and 1000 degrees C demonstrated characteristic spectra of Eu3+ ions as well as were measured the emission spectra of Eu2+ ions for the samples calcinated at 700 degrees C. The effect of MgAl2O4 grain sizes on luminescence properties was noticed. To explain these differences a detailed analysis of luminescence spectra by the Judd-Ofelt theory has been performed.

  18. Yield Strength of Transparent MgAl2O4 Nano-Ceramic at High Pressure and Temperature

    PubMed Central

    2010-01-01

    We report here experimental results of yield strength and stress relaxation measurements of transparent MgAl2O4 nano-ceramics at high pressure and temperature. During compression at ambient temperature, the differential strain deduced from peak broadening increased significantly with pressure up to 2 GPa, with no clear indication of strain saturation. However, by then, warming the sample above 400°C under 4 GPa, stress relaxation was obviously observed, and all subsequent plastic deformation cycles are characterized again by peak broadening. Our results reveal a remarkable reduction in yield strength as the sintering temperature increases from 400 to 900°C. The low temperature for the onset of stress relaxation has attracted attention regarding the performance of transparent MgAl2O4 nano-ceramics as an engineering material. PMID:20676198

  19. Effect of calcination temperature on Mg-Al bimetallic oxides as sorbents for the removal of F(-) in aqueous solutions.

    PubMed

    Moriyama, Sayo; Sasaki, Keiko; Hirajima, Tsuyoshi

    2014-01-01

    Bimetallic oxides were synthesized from hydrotalcite using increasing calcination temperatures (873, 1073, 1273 K). These bimetallic oxides were fully characterized and the sorption density of F(-) was investigated. X-ray diffraction patterns for the produced bimetallic oxides showed that MgO was the primary phase within the range of investigated calcination temperatures, but MgO crystallinity increased with calcination temperature and an additional MgAl2O4 phase was formed. In the process of F(-) sorption, the bimetallic oxides were primarily transformed into hydrotalcite with intercalation of F(-). The Higher calcination temperature increased the MgAl2O4 phase, which did not contribute to the immobilization of F(-). These findings show that optimizing the calcination temperature can be used to maximize the sorption density of this material for F(-) removal. Copyright © 2013 Elsevier Ltd. All rights reserved.

  20. Au on MgAl2O4 spinels: The effect of support surface properties in glycerol oxidation

    SciTech Connect

    Villa, Alberto; Gaiassi, Aureliano; Rossetti, Ilenia; Bianchi, Claudia; van Benthem, Klaus; Veith, Gabriel M; Prati, Laura

    2010-01-01

    Here we investigated the properties of Au nanoparticles, prepared via three different techniques and supported on three different MgAl2O4 spinels. The surface composition and area of the spinel plays an important role in determining the selectivity of the catalyst in the selective oxidation of glycerol. it was found that aluminum rich surfaces enhance the C-C bond cleavage reaction for large gold particles which is opposite of what is normally observed for large clusters which typically show no C-C cleavage. We also report that similarly sized AuNPs on the different MgAl2O4 spinels with the same surface Al/Mg ratio, show a similar selectivity; however activity depends on surface area.

  1. Recent developments in TiNi-based shape memory alloys

    NASA Astrophysics Data System (ADS)

    Miyazaki, Shuichi; Kohl, Manfred

    1998-07-01

    Recently, a variety of manufacturing methods have enabled us to produce fine or thin shapes or unique structure of TiNi-based shape memory alloys: e.g., (a) rolled thin plates with a thickness less than 100 μm, (b) drawn fine wires with a diameter less than 50 μm, (c) drawn microtubes with an outer diameter less than 350 μm, (d) sputter-deposited thin films with a thickness less than 1 μm, (e) rapidly solidified ribbons of several tens μm thickness and (f) sintered porous structured materials. The characteristics and applications of these TiNi-based alloys are reviewed.

  2. The effect of selected alloying element additions on properties of Mg-based alloy as bioimplants: A literature review

    NASA Astrophysics Data System (ADS)

    Zhang, Li-Nan; Hou, Zeng-Tao; Ye, Xin; Xu, Zhao-Bin; Bai, Xue-Ling; Shang, Peng

    2013-09-01

    This review investigates the current application limitations of Mg and Mg alloys. The key issues hindering the application of biodegradable Mg alloys as implants are their fast degradation rate and biological consideration. We have discussed the effect of some selected alloying element additions on the properties of the Mg-based alloy, especially the nutrient elements in human (Zn, Mn, Ca, Sr). Different grain sizes, phase constituents and distributions consequently influence the mechanical properties of the Mg alloys. Solution strengthening and precipitation strengthening are enhanced by the addition of alloying elements, generally improving the mechanical properties. Besides, the hot working process can also improve the mechanical properties. Combination of different processing steps is suggested to be adopted in the fabrication of Mg-based alloys. Corrosion properties of these Mg-based alloys have been measured in vitro and in vivo. The degradation mechanism is also discussed in terms of corrosion types, rates, byproducts and response of the surrounding tissues. Moreover, the clinical response and requirements of degradable implants are presented, especially for the nutrient elements (Ca, Mn, Zn, Sr). This review provides information related to different Mg alloying elements and presents the promising candidates for an ideal implant.

  3. Corrosion of MgO-MgAl{sub 2}O{sub 4} spinel refractory bricks by calcium aluminosilicate slag

    SciTech Connect

    Goto, Kiyoshi; Argent, B.B.; Lee, W.E.

    1997-02-01

    Microstructural analysis of MgO-MgAl{sub 2}O{sub 4} refractory bricks corroded at 1,400--1,500 C by calcium aluminosilicate slag reveals secondary spinel, monticellite, merwinite, and MgO as microscopic corrosion products, generally forming in this sequence as the brick is penetrated. The secondary spinel forms an incomplete layer close to (but not at) the MgO grain. Thermodynamic calculations are used to support a detailed model of the corrosion mechanism.

  4. In Situ Synthesis of 3Y-TZP/MgAl2O4 Nanoparticle Composite Through Co-precipitation

    NASA Astrophysics Data System (ADS)

    Opoku, Michael; Kanakala, Raghunath

    2016-06-01

    3 Mole pct yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) and spinel (MgAl2O4) nanocomposite was synthesized by co-precipitation—calcination method. The powders were made to a composition of 70 vol pct 3Y-TZP and 30 vol pct MgAl2O4. The composite made of 70 pct 3Y-TZP and 30 pct MgAl2O4 is well known for its superplastic ability at high temperatures. Reverse drop method was utilized to precipitate metal ions simultaneously, resulting in a homogenous composition on a molecular scale and crystalline after calcination at 1273 K (1000 °C) for 2 hours. The characterization results showed that the powders were phase pure tetragonal zirconia and spinel, fairly not forming a ternary complex between Spinel and 3Y-TZP. From the TEM and DLS analyses, the average particle size was determined to be about 50 to 100 nm with some level of agglomeration. Raman peaks E g (156 cm-1), E g (274 cm-1), B 1g (332 cm-1), E g (474 cm-1), A 1g (605 cm-1), and B 1g (653 cm-1), due to the tetragonal phase of 3Y-TZP and E g (487 cm-1) due to cubic phase of MgAl2O4, are observed in the sample. HRTEM results show interplanar spacing of (311) of the spinel and (101) of the yttria-stabilized zirconia, which indicates the high-level homogeneity in the nanoparticle composite powders.

  5. Effect of Iron Impurity on the Phase Composition, Structure and Properties of Magnesium Alloys Containing Manganese and Aluminum

    NASA Astrophysics Data System (ADS)

    Volkova, E. F.

    2017-07-01

    Results of a study of the interaction between iron impurity and manganese and aluminum alloying elements during formation of phase composition in alloys of the Mg - Mn, Mg - Al, Mg - Al - Mn, and Mg - Al - Zn - Mn systems are presented. It is proved that this interaction results in introduction of Fe into the intermetallic phase. The phase compositions of model magnesium alloys and commercial alloys MA2-1 and MA5 are studied. It is shown that both manganese and aluminum may bind the iron impurity into phases. Composite Fe-containing intermetallic phases of different compositions influence differently the corrosion resistance of magnesium alloys.

  6. Degradation of chlorophenols by supported Co-Mg-Al layered double hydrotalcite with bicarbonate activated hydrogen peroxide.

    PubMed

    Jawad, Ali; Lu, Xiaoyan; Chen, Zhuqi; Yin, Guochuan

    2014-10-30

    Toxic and bioresistant compounds have attracted researchers to develop more efficient and cost-effective technologies for degradation of organic compounds in wastewater. This work demonstrates the degradation of 4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, and phenol as model compounds using bicarbonate-activated H2O2 oxidation system in the presence of supported catalysts. The catalytic activity of the catalyst was investigated in term of degradation of target compounds, chemical oxygen demand (COD), and total organic carbon (TOC) removals both for batch mode and in fixed bed reactor using CoMgAl-HTs and CoMgAl-SHTs, respectively. The leaching of cobalt ion was efficiently prohibited because of the presence of a weakly basic medium provided by bicarbonate, and the CoMgAl-SHTs catalyst was found to retain its stability and good catalytic activity in fixed bed reactor for over 300 h. Extensive chemical probing, fluorescence, and electron paired resonance (EPR) studies were conducted to identify the actual reactive species in the degradation pathway, which revealed that the reaction proceeds through generation of superoxide, hydroxyl radical along with carbonate radical.

  7. Improved Hydrogen Storage Properties of Mg(BH4)2-Mg(AlH4)2 Combined Systems

    NASA Astrophysics Data System (ADS)

    Xiao, Haoyuan; Leng, Haiyan; Yu, Zhigang; Li, Qian; Chou, Kuo-Chih

    Magnesium borohydride and Magnesium alanate were synthesized by mechanochemical metathesis reaction. The thermal decomposition behaviors of Mg(BH4)2-nMg(AlH4)2(n=0.5,1) systems were investigated as potential hydrogen storage materials. The results showed that the systems started to desorb H2 at 120 °C and desorbed 3.9 wt.% and 4.9 wt.% H2 below 300 °C when n equals 0.5 and 1, respectively, while individual Mg(BH4)2 started to desorb H2 at 250 °C and desorbed only 0.82 wt.% H2. Because of the exist of the Mg(AlH4)2, the isothermal desorption kinetics of Mg(BH4)2 in the Mg(BH4)2-0.5Mg(AlH4)2 systems was 50% faster than that of pristine Mg(BH4)2. In addition, the re-hydrogenation rates also increased 49.4% and 37.9%.

  8. Cr{sub 2}Nb-based alloy development

    SciTech Connect

    Liu, C.T.; Tortorelli, P.F.; Horton, J.A.; Easton, D.S.; Heatherly, L.

    1996-06-01

    The objective of this work is to develop a new generation of structural materials based on intermetallic alloys for use at high temperatures in advanced fossil energy conversion systems. Target applications of such ultrahigh strength alloys include hot components (for example, air heat exchangers) in advanced energy conversion systems and heat engines. However, these materials may also find use as wear-resistant parts in coal handling systems (for example, nozzles), drill bits for oil/gas wells, and valve guides in diesel engines. One potential class of such alloys is that based on Cr-Cr{sub 2}Nb alloys. The intermetallic phase, Cr{sub 2}Nb, with a complex cubic structure (C-15) has been selected for initial development because of its high melting point (1770{degrees}C), relatively low material density (7.7 g/cm{sup 2}), and excellent high-temperature strength (at 1000 to 1250{degrees}C). This intermetallic phase, like many other Laves phases, has a wide range of compositional homogeneity suggesting the possibility of improving its mechanical and metallurgical properties by alloying additions.

  9. 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.

  10. Recrystallization characteristics of oxide dispersion strengthened nickel-base alloys

    NASA Technical Reports Server (NTRS)

    Hotzler, R. K.; Glasgow, T. K.

    1980-01-01

    Electron microscopy was employed to study the process of recrystallization in two oxide dispersion strengthened (ODS) mechanically alloyed nickel-base alloys, MA 754 and MA 6000E. MA 754 contained both fine, uniformly dispersed particles and coarser oxides aligned along the working direction. Hot rolled MA 754 had a grain size of 0.5 microns and high dislocation densities. After partial primary recrystallization, the fine grains transformed to large elongated grains via secondary (or abnormal) grain growth. Extruded and rolled MA 6000E contained equiaxed grains of 0.2 micron diameter. Primary recrystallization occurring during working eliminated virtually all dislocations. Conversion from fine to coarse grains was triggered by gamma prime dissolution; this was also a process of secondary or abnormal grain growth. Comparisons were made to conventional and oxide dispersion strengthened nickel-base alloys.

  11. Effects of Heat Treatment on the Discharge Behavior of Mg-6wt.%Al-1wt.%Sn Alloy as Anode For Magnesium-Air Batteries

    NASA Astrophysics Data System (ADS)

    Xiong, Hanqing; Zhu, Hualong; Luo, Jie; Yu, Kun; Shi, Chunli; Fang, Hongjie; Zhang, Yu

    2017-05-01

    Mg-6wt.%Al-1wt.%Sn alloys under different conditions are prepared. Primary magnesium-air batteries are assembled using such experimental Mg-Al-Sn alloys as anodes. The discharge behaviors of different alloys are investigated in 3.5 wt.% NaCl solution. The results show that the solution treatment can facilitate the homogeneous distribution of alloy elements and reduce the accumulation of discharge products. The magnesium-air battery based on the solution-treated Mg-Al-Sn anode presents higher operating voltage and more stable discharge process than those on the as-cast and the aged ones. Although the solution treatment cannot effectively improve the capacity density and the anodic efficiency of the experimental Mg-Al-Sn alloy, it is an effective approach to increasing the power and the energy density during discharge process. Especially at the applied current density of 30 mA cm-2 for 5 h, the solution-treated anode supplies 1.212 V average operating voltage, the anode energy density reaches 1527.2 mWhg-1, while the cast one is 1481.3 mWhg-1 and the aged one is 1478.8 mWhg-1.

  12. Pd-Ag Membrane Coupled to a Two-Zone Fluidized Bed Reactor (TZFBR) for Propane Dehydrogenation on a Pt-Sn/MgAl2O4 Catalyst

    PubMed Central

    Medrano, José-Antonio; Julián, Ignacio; Herguido, Javier; Menéndez, Miguel

    2013-01-01

    Several reactor configurations have been tested for catalytic propane dehydrogenation employing Pt-Sn/MgAl2O4 as a catalyst. Pd-Ag alloy membranes coupled to the multifunctional Two-Zone Fluidized Bed Reactor (TZFBR) provide an improvement in propane conversion by hydrogen removal from the reaction bed through the inorganic membrane in addition to in situ catalyst regeneration. Twofold process intensification is thereby achieved when compared to the use of traditional fluidized bed reactors (FBR), where coke formation and thermodynamic equilibrium represent important process limitations. Experiments were carried out at 500–575 °C and with catalyst mass to molar flow of fed propane ratios between 15.1 and 35.2 g min mmol−1, employing three different reactor configurations: FBR, TZFBR and TZFBR + Membrane (TZFBR + MB). The results in the FBR showed catalyst deactivation, which was faster at high temperatures. In contrast, by employing the TZFBR with the optimum regenerative agent flow (diluted oxygen), the process activity was sustained throughout the time on stream. The TZFBR + MB showed promising results in catalytic propane dehydrogenation, displacing the reaction towards higher propylene production and giving the best results among the different reactor configurations studied. Furthermore, the results obtained in this study were better than those reported on conventional reactors. PMID:24958620

  13. Pd-Ag Membrane Coupled to a Two-Zone Fluidized Bed Reactor (TZFBR) for Propane Dehydrogenation on a Pt-Sn/MgAl2O4 Catalyst.

    PubMed

    Medrano, José-Antonio; Julián, Ignacio; Herguido, Javier; Menéndez, Miguel

    2013-05-14

    Several reactor configurations have been tested for catalytic propane dehydrogenation employing Pt-Sn/MgAl2O4 as a catalyst. Pd-Ag alloy membranes coupled to the multifunctional Two-Zone Fluidized Bed Reactor (TZFBR) provide an improvement in propane conversion by hydrogen removal from the reaction bed through the inorganic membrane in addition to in situ catalyst regeneration. Twofold process intensification is thereby achieved when compared to the use of traditional fluidized bed reactors (FBR), where coke formation and thermodynamic equilibrium represent important process limitations. Experiments were carried out at 500-575 °C and with catalyst mass to molar flow of fed propane ratios between 15.1 and 35.2 g min mmol-1, employing three different reactor configurations: FBR, TZFBR and TZFBR + Membrane (TZFBR + MB). The results in the FBR showed catalyst deactivation, which was faster at high temperatures. In contrast, by employing the TZFBR with the optimum regenerative agent flow (diluted oxygen), the process activity was sustained throughout the time on stream. The TZFBR + MB showed promising results in catalytic propane dehydrogenation, displacing the reaction towards higher propylene production and giving the best results among the different reactor configurations studied. Furthermore, the results obtained in this study were better than those reported on conventional reactors.

  14. In vitro corrosion of dental Au-based casting alloys in polyvinylpyrrolidone-iodine solution.

    PubMed

    Takasusuki, Norio; Ida, Yusuke; Hirose, Yukito; Ochi, Morio; Endo, Kazuhiko

    2013-01-01

    The corrosion and tarnish behaviors of two Au-based casting alloys (ISO type 1 and type 4 Au alloys) and their constituent pure metals, Au, Ag, Cu, Pt, and Pd in a polyvinylpyrrolidone-iodine solution were examined. The two Au alloys actively corroded, and the main anodic reaction for both was dissolution of Au as AuI₂(-). The amount of Au released from the ISO type 1 Au alloy was significantly larger than that from the ISO type 4 Au alloy (P<0.05). Visible light spectrophotometry revealed that the type 1 alloy exhibited higher susceptibility to tarnishing than the type 4 alloy. The corrosion forms of the two Au alloys were found to be completely different, i.e., the type 1 alloy exhibited the corrosion attack over the entire exposed surface with a little irregularity whereas the type 4 alloy exhibited typical intergranular corrosion, which was caused by local cells produced by segregation of Pd and Pt.

  15. e/a determination for 4d- and 5d-transition metal elements and their intermetallic compounds with Mg, Al, Zn, Cd and In

    NASA Astrophysics Data System (ADS)

    Mizutani, U.; Sato, H.; Inukai, M.; Zijlstra, E. S.

    2013-08-01

    The present work is devoted to the determination of the effective electrons per atom ratio e/a by means of first-principles full-potential linearized augmented plane wave-Fourier method for elements from Rb to Ag in Period 5 and from Cs to Au in Period 6 of the periodic table and is regarded as a continuation of the preceding work done for elements from K to Cu in Period 4. The value of e/a was determined by reading off the square of the Fermi diameter, ? from the dispersion relation for electrons outside the Muffin-Tin spheres. A straightforward reading of the ordinate at the Fermi level, i.e. local reading method was validated for Rb and Cs in Group 1, Sr in Group 2, Y in Group 3, Pd and Pt in Group 10 and Ag and Au in Group 11. Instead, the nearly free electron (NFE) method was found to be indispensable for TM elements from Zr to Rh in Period 5 and those from Ba to Ir in Period 6. The composition dependence of e/a values for intermetallic compounds in X-TM (X = Mg, Al, Zn, Cd and In) alloy systems was also studied. The new Hume-Rothery electron concentration rule was established by constructing e/uc, the number of electrons per unit cell, vs. square of critical reciprocal lattice vector, ? , diagram for structurally complex metallic alloys having a pseudogap at the Fermi level. A proper use of either the local reading- or the NFE-e/a for the elements as indicated above is found to be essential.

  16. Environmental effects in NiTi-based alloys

    SciTech Connect

    Zhu, J.H.; Liu, C.T.

    1999-06-04

    Environmental embrittlement has been identified as one of the major causes for low ductility and poor fracture toughness in a number of ordered intermetallics containing reactive element,s such as Al, Ti, Si, Mn, V or Mo, when tested in moisture-containing environments at room temperature. This is believed to be a hydrogen embrittlement process which involves the reaction of reactive elements in intermetallic alloys with water vapor in air, and subsequent generation of atomic hydrogen that is transported into the interior of the specimen, leading to brittle crack propagation and fracture along grain boundaries and/or cleavage planes. In this communication, the authors report the tensile properties in different environments of two NiTi-based alloys with ordered B19 and B2 structures. The alloys were tested under controlled environments to observe the effects of moisture and hydrogen gas on the ductility of the alloys. The fracture surface observation shows that, consistent with the tensile test properties, the fracture mode doe snot change when tested in different environments. All the alloys showed ductile fracture, consistent with the good ductility of the materials.

  17. The Bain path of paramagnetic Fe-Cr based alloys

    NASA Astrophysics Data System (ADS)

    Al-Zoubi, N.; Johansson, B.; Nilson, G.; Vitos, L.

    2011-07-01

    Employing the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation, we calculated the total energy and local magnetic moments of paramagnetic Fe-Cr-M (M = Cr, Mn, Fe, Co, Ni) alloys along the tetragonal distortion (Bain) path connecting the body centered cubic (bcc) and the face centered cubic (fcc) structures. The paramagnetic phase is modeled by the disordered local magnetic moment scheme. For all alloys, the local magnetic moments on Fe atoms decrease from the maximum value corresponding to the bcc phase toward the minimum value realized for the fcc phase. Cobalt atoms have non-vanishing local magnetic moments only for tetragonal lattices with c/a < 1.30, whereas the local magnetic moments of Mn show weak crystal structure dependence. We find that Cr stabilizes the bcc lattice and increases the energy barrier as going from the bcc toward the fcc phase. Both Co and Ni favor the fcc lattice and decrease the energy barrier relative to the bcc phase. On the other hand, the tetragonal distortion around the fcc phase is facilitated by Cr and to a somewhat lesser extent also by Ni, but strongly impeded by Co. Manganese has negligible effect on the structural energy difference as well as on the energy barrier along the Bain path. Our findings on the alloying induced softening or hardening of Fe-Cr based alloys against tetragonal distortions are important for understanding the interstitial driven martensitic transformations in alloy steels.

  18. Advanced nickel base alloys for high strength, corrosion applications

    DOEpatents

    Flinn, J.E.

    1998-11-03

    Improved nickel-base alloys of enhanced strength and corrosion resistance, produced by atomization of an alloy melt under an inert gas atmosphere and of composition 0--20Fe, 10--30Cr, 2--12Mo, 6 max. Nb, 0.05--3 V, 0.08 max. Mn, 0.5 max. Si, less than 0.01 each of Al and Ti, less than 0.05 each of P and S, 0.01--0.08C, less than 0.2N, 0.1 max. 0, bal. Ni. 3 figs.

  19. Advanced nickel base alloys for high strength, corrosion applications

    DOEpatents

    Flinn, John E.

    1998-01-01

    Improved nickel-base alloys of enhanced strength and corrosion resistance, produced by atomization of an alloy melt under an inert gas atmosphere and of composition 0-20Fe, 10-30Cr, 2-12Mo, 6 max. Nb, 0.05-3 V, 0.08 max. Mn, 0.5 max. Si, less than 0.01 each of Al and Ti, less than 0.05 each of P and S, 0.01-0.08C, less than 0.2N, 0.1 max. 0, bal. Ni.

  20. Hot corrosion of S-57, 1 cobalt-base alloy

    NASA Technical Reports Server (NTRS)

    Santoro, G. J.

    1977-01-01

    A cobalt base alloy, S-57, was hot corrosion tested in Mach 0.3 burner rig combustion gases at maximum alloy temperatures of 900 and 1000 C. Various salt concentrations were injected into the burner: 0.5, 2, 5, and 10 ppm synthetic sea salt and 4 ppm sodium sulfate (Na2SO4). S-57 underwent accelerated corrosion only under the most severe test conditions, for example, 4 ppm Na2SO4 at 900 C. The process of the accelerated corrosion was primarily sulfidation.

  1. Improved Mg-based alloys for hydrogen storage

    SciTech Connect

    Sapru, K.; Ming, L.; Stetson, N.T.; Evans, J.

    1998-08-01

    The overall objective of this on-going work is to develop low temperature alloys capable of reversibly storing at least 3 wt.% hydrogen, allowing greater than for 2 wt.% at the system level which is required by most applications. Surface modification of Mg can be used to improve its H-sorption kinetics. The authors show here that the same Mg-transition metal-based multi-component alloy when prepared by melt-spinning results in a more homogeneous materials with a higher plateau pressure as compared to preparing the material by mechanical grinding. They have also shown that mechanically alloyed Mg{sub 50}Al{sub 45}Zn{sub 5} results in a sample having a higher plateau pressure.

  2. Enhanced Corrosion Resistance of Iron-Based Amorphous Alloys

    SciTech Connect

    Rebak, R B; Day, S D; Lian, T; Aprigliano, L F; Hailey, P D; Farmer, J C

    2007-02-18

    Iron-based amorphous alloys possess enhanced hardness and are highly resistant to corrosion, which make them desirable for wear applications in corrosive environments. It was of interest to examine the behavior of amorphous alloys during anodic polarization in concentrated salt solutions and in the salt-fog testing. Results from the testing of one amorphous material (SAM2X5) both in ribbon form and as an applied coating are reported here. Cyclic polarization tests were performed on SAM2X5 ribbon as well as on other nuclear engineering materials. SAM2X5 showed the highest resistance to localized corrosion in 5 M CaCl{sub 2} solution at 105 C. Salt fog tests of 316L SS and Alloy 22 coupons coated with amorphous SAM2X5 powder showed resistance to rusting. Partial devitrification may be responsible for isolated pinpoint rust spots in some coatings.

  3. Nickel base alloy. [for gas turbine engine stator vanes

    NASA Technical Reports Server (NTRS)

    Freche, J. C.; Waters, W. J. (Inventor)

    1977-01-01

    A nickel base superalloy for use at temperatures of 2000 F (1095 C) to 2200 F (1205 C) was developed for use as stator vane material in advanced gas turbine engines. The alloy has a nominal composition in weight percent of 16 tungsten, 7 aluminum, 1 molybdenum, 2 columbium, 0.3 zirconium, 0.2 carbon and the balance nickel.

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

    PubMed

    Kameda, Tomohito; Kondo, Eisuke; Yoshioka, Toshiaki

    2015-03-15

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

  5. FIRST-PRINCIPLES CALCULATIONS OF CHARGE STATES AND FORMATION ENERGIES OF Mg, Al, and Be TRANSMUTANTS IN 3C-SiC

    SciTech Connect

    Hu, Shenyang Y.; Setyawan, Wahyu; Jiang, Weilin; Henager, Charles H.; Kurtz, Richard J.

    2014-08-28

    The Vienna Ab-initio Simulation Package (VASP) is employed to calculate charge states and the formation energies of Mg, Al and Be transmutants at different lattice sites in 3C-SiC. The results provide important information on the dependence of the most stable charge state and formation energy of Mg, Al, Be and vacancies on electron potentials.

  6. Bulk amorphous steels based on Fe alloys

    DOEpatents

    Lu, ZhaoPing; Liu, Chain T.

    2006-05-30

    A bulk amorphous alloy has the approximate composition: Fe.sub.(100-a-b-c-d-e)Y.sub.aMn.sub.bT.sub.cM.sub.dX.sub.e wherein: T includes at least one of the group consisting of: Ni, Cu, Cr and Co; M includes at least one of the group consisting of W, Mo, Nb, Ta, Al and Ti; X includes at least one of the group consisting of Co, Ni and Cr; a is an atomic percentage, and a<5; b is an atomic percentage, and b.ltoreq.25; c is an atomic percentage, and c.ltoreq.25; d is an atomic percentage, and d.ltoreq.25; and e is an atomic percentage, and 5.ltoreq.e.ltoreq.30.

  7. NOREM wear-resistant, iron-based hard-facing alloys: Final report

    SciTech Connect

    Grobner, P.; Ohriner, E.K.; Wada, T.; Whelan, E.P.

    1989-07-01

    Wear-resistance cobalt-free hardfacing alloys are needed to replace the cobalt-base alloys used to hardface nuclear valves in order to reduce the exposure of maintenance personnel. Some thirty heats of cast iron-base alloys were prepared and characterized. Selected heats were prepared and applied as hardfacing overlays on austenitic steel substrates using both GTA and PTA welding processes. Some of the iron-base alloys exhibited galling wear resistance as high as that of cobalt-base standards both in the cast condition and in the PTA overlays. Hardness, mechanical properties, and galling wear resistance were determined on weld overlays and on cast alloys. Dilution and thermal expansivity were determined for weld overlays. X-ray diffraction and scanning electron microscopy were used to determine the alloys' microstructures. Other commercially available alloys were tested for galling wear resistance and compared to iron-base alloys. 7 refs., 2 figs., 2 tabs.

  8. Zirconium-based alloys, nuclear fuel rods and nuclear reactors including such alloys, and related methods

    DOEpatents

    Mariani, Robert Dominick

    2014-09-09

    Zirconium-based metal alloy compositions comprise zirconium, a first additive in which the permeability of hydrogen decreases with increasing temperatures at least over a temperature range extending from 350.degree. C. to 750.degree. C., and a second additive having a solubility in zirconium over the temperature range extending from 350.degree. C. to 750.degree. C. At least one of a solubility of the first additive in the second additive over the temperature range extending from 350.degree. C. to 750.degree. C. and a solubility of the second additive in the first additive over the temperature range extending from 350.degree. C. to 750.degree. C. is higher than the solubility of the second additive in zirconium over the temperature range extending from 350.degree. C. to 750.degree. C. Nuclear fuel rods include a cladding material comprising such metal alloy compositions, and nuclear reactors include such fuel rods. Methods are used to fabricate such zirconium-based metal alloy compositions.

  9. Electrochemical hydrogen storage alloys and batteries fabricated from Mg containing base alloys

    DOEpatents

    Ovshinsky, Stanford R.; Fetcenko, Michael A.

    1996-01-01

    An electrochemical hydrogen storage material comprising: (Base Alloy).sub.a M.sub.b where, Base Alloy is an alloy of Mg and Ni in a ratio of from about 1:2 to about 2:1, preferably 1:1; M represents at least one modifier element chosen from the group consisting of Co, Mn, Al, Fe, Cu, Mo, W, Cr, V, Ti, Zr, Sn, Th, Si, Zn, Li, Cd, Na, Pb, La, Mm, and Ca; b is greater than 0.5, preferably 2.5, atomic percent and less than 30 atomic percent; and a+b=100 atomic percent. Preferably, the at least one modifier is chosen from the group consisting of Co, Mn, Al, Fe, and Cu and the total mass of the at least one modifier element is less than 25 atomic percent of the final composition. Most preferably, the total mass of said at least one modifier element is less than 20 atomic percent of the final composition.

  10. Ni3Al-based alloys for die and tool application

    DOEpatents

    Liu, Chain T.; Bloom, Everett E.

    2001-01-01

    A novel Ni.sub.3 Al-based alloy exhibits strengths and hardness in excess of the standard base alloy IC-221M at temperatures of up to about 1000.degree. C. The alloy is useful in tool and die applications requiring such temperatures, and for structural elements in engineering systems exposed to such temperatures.

  11. Layer-by-layer assembly of luminescent ultrathin films by Mg-Al-Eu LDHs nanosheets and organic ligand with high transparency

    NASA Astrophysics Data System (ADS)

    Zhang, Wenjun; Li, Yanlin; Fan, Hongxian

    2016-01-01

    We fabricated a kind of luminescent ordered multilayer transparent ultrathin films (OMTFs) based on inorganic rare earth doped layered double hydroxides (Mg-Al-Eu LDHs) nanosheets and the organic ligand 2-thenoyltrifluoroacetone (TTA) via layer-by-layer assembly method. At the same time, Polyvinyl Alcohol (PVA) aqueous solution was used as intermediate linkers. UV-visible absorption spectroscopy, X-ray diffraction, fluorescence spectroscopy and scanning electron microscopy were introduced to investigate the structure and properties of these films. Surprisingly, the uniformity and the fluorescence emission intensity of OMTFs which utilized polyvinyl Alcohol (PVA) as intermediate linkers are significantly enhanced compared with that of OMTFs without PVA. Herein, it was found that the fluorescence emission intensity of this kind of ultrathin film with PVA displays a monotonic increase as the number of deposition cycles increasing, and further the films which are highly transparent, uniform and ultrathin have potential applications in the optical display devices.

  12. Thermal evolution of Mg-Al and Ni-Al layered double hydroxides: the structure of the dehydrated phase.

    PubMed

    Cherepanova, Svetlana; Leont'eva, Natalya; Drozdov, Vladimir; Doronin, Vladimir

    2016-11-01

    Simulation of X-ray diffraction patterns on the basis of the models of one-dimensional disordered crystals was used to investigate the structure of the dehydrated phase produced by dehydration of Mg-Al and Ni-Al layered double hydroxides at a temperature of ∼473-498 K. It was found that the removal of water molecules transforms the initial structure, which is a mixture of 3R1 and 2H1 polytypes, into a structure that comprises preferentially fragments of 3R2 and 1H polytypes and has some turbostratic disorder.

  13. Monolithic translucent BaMgAl10O17:Eu2+ phosphors for laser-driven solid state lighting

    NASA Astrophysics Data System (ADS)

    Cozzan, Clayton; Brady, Michael J.; O'Dea, Nicholas; Levin, Emily E.; Nakamura, Shuji; DenBaars, Steven P.; Seshadri, Ram

    2016-10-01

    With high power light emitting diodes and laser diodes being explored for white light generation and visible light communication, thermally robust encapsulation schemes for color-converting inorganic phosphors are essential. In the current work, the canonical blue-emitting phosphor, high purity Eu-doped BaMgAl10O17, has been prepared using microwave-assisted heating (25 min) and densified into translucent ceramic phosphor monoliths using spark plasma sintering (30 min). The resulting translucent ceramic monoliths convert UV laser light to blue light with the same efficiency as the starting powder and provide superior thermal management in comparison with silicone encapsulation.

  14. Monolithic translucent BaMgAl10O17:Eu2+ phosphors for laser-driven solid state lighting

    DOE PAGES

    Cozzan, Clayton; Brady, Michael J.; O’Dea, Nicholas; ...

    2016-10-11

    With high power light emitting diodes and laser diodes being explored for white light generation and visible light communication, thermally robust encapsulation schemes for color-converting inorganic phosphors are essential. In the current work, the canonical blue-emitting phosphor, high purity Eu-doped BaMgAl10O17, has been prepared using microwave-assisted heating (25 min) and densified into translucent ceramic phosphor monoliths using spark plasma sintering (30 min). Lastly, the resulting translucent ceramic monoliths convert UV laser light to blue light with the same efficiency as the starting powder and provide superior thermal management in comparison with silicone encapsulation.

  15. Nickel-base alloy GTD-222, a new gas turbine nozzle alloy

    SciTech Connect

    Seaver, D.W.; Beltran, A.M. )

    1993-01-01

    This paper summarizes the key properties of GTD-222 (Wood and Haydon, 1989), a new cast nickel-base nozzle alloy developed by GE for use in land-based gas turbines. GTD-222 is being introduced as a replacement for FSX-414 in second and third-stage nozzles of certain machines. Presented in this paper are comparisons of the tensile, creep-rupture, and fatigue properties of GTD-222 versus FSX-414. In addition, the results of a long-term thermal stability study, high-temperature oxidation, and hot corrosion evaluation as well as weldability results will be discussed.

  16. Analysis of thermoelectric properties of high-temperature complex alloys of nickel-base, iron-base and cobalt-base groups

    NASA Technical Reports Server (NTRS)

    Holanda, R.

    1984-01-01

    The thermoelectric properties alloys of the nickel-base, iron-base, and cobalt-base groups containing from 1% to 25% 106 chromium were compared and correlated with the following material characteristics: atomic percent of the principle alloy constituent; ratio of concentration of two constituents; alloy physical property (electrical resistivity); alloy phase structure (percent precipitate or percent hardener content); alloy electronic structure (electron concentration). For solid-solution-type alloys the most consistent correlation was obtained with electron concentration, for precipitation-hardenable alloys of the nickel-base superalloy group, the thermoelectric potential correlated with hardener content in the alloy structure. For solid-solution-type alloys, no problems were found with thermoelectric stability to 1000; for precipitation-hardenable alloys, thermoelectric stability was dependent on phase stability. The effects of the compositional range of alloy constituents on temperature measurement uncertainty are discussed.

  17. Elevated temperature tribology of cobalt and tantalum-based alloys

    DOE PAGES

    Scharf, T. W.; Prasad, S. V.; Kotula, P. G.; ...

    2014-12-31

    This paper describes the friction and wear behavior of a Co–Cr alloy sliding on a Ta–W alloy. Measurements were performed in a pin-on-flat configuration with a hemispherically tipped Co-base alloy pin sliding on a Ta–W alloy flat from ambient to 430°C. Focused ion beam-scanning electron microscopy (FIB-SEM) and cross-sectional transmission electron microscopy (TEM) were used to identify the friction-induced changes to the chemistry and crystal structure in the subsurface regions of wear tracks. During sliding contact, transfer of material varied as a function of the test temperature, either from pin-to-flat, flat-to-pin, or both, resulting in either wear loss and/or volumemore » gain. Friction coefficients (μ) and wear rates also varied as a function of test temperature. The lowest friction coefficient (μ=0.25) and wear rate (1×10–4 mm3/N•m) were observed at 430°C in argon atmosphere. This was attributed to the formation of a Co-base metal oxide layer (glaze), predominantly (Co, Cr)O with Rocksalt crystal structure, on the pin surface. Part of this oxide film transferred to the wear track on Ta–W, providing a self-mated oxide-on-oxide contact. Once the oxide glaze is formed, it is able to provide friction reduction for the entire temperature range of this study, ambient to 430°C. Furthermore, the results of this study indicate that glazing the surfaces of Haynes alloys with continuous layers of cobalt chrome oxide prior to wear could protect the cladded surfaces from damage.« less

  18. Elevated temperature tribology of cobalt and tantalum-based alloys

    SciTech Connect

    Scharf, T. W.; Prasad, S. V.; Kotula, P. G.; Michael, J. R.; Robino, C. V.

    2014-12-31

    This paper describes the friction and wear behavior of a Co–Cr alloy sliding on a Ta–W alloy. Measurements were performed in a pin-on-flat configuration with a hemispherically tipped Co-base alloy pin sliding on a Ta–W alloy flat from ambient to 430°C. Focused ion beam-scanning electron microscopy (FIB-SEM) and cross-sectional transmission electron microscopy (TEM) were used to identify the friction-induced changes to the chemistry and crystal structure in the subsurface regions of wear tracks. During sliding contact, transfer of material varied as a function of the test temperature, either from pin-to-flat, flat-to-pin, or both, resulting in either wear loss and/or volume gain. Friction coefficients (μ) and wear rates also varied as a function of test temperature. The lowest friction coefficient (μ=0.25) and wear rate (1×10–4 mm3/N•m) were observed at 430°C in argon atmosphere. This was attributed to the formation of a Co-base metal oxide layer (glaze), predominantly (Co, Cr)O with Rocksalt crystal structure, on the pin surface. Part of this oxide film transferred to the wear track on Ta–W, providing a self-mated oxide-on-oxide contact. Once the oxide glaze is formed, it is able to provide friction reduction for the entire temperature range of this study, ambient to 430°C. Furthermore, the results of this study indicate that glazing the surfaces of Haynes alloys with continuous layers of cobalt chrome oxide prior to wear could protect the cladded surfaces from damage.

  19. Tungsten wire-nickel base alloy composite development

    NASA Technical Reports Server (NTRS)

    Brentnall, W. D.; Moracz, D. J.

    1976-01-01

    Further development and evaluation of refractory wire reinforced nickel-base alloy composites is described. Emphasis was placed on evaluating thermal fatigue resistance as a function of matrix alloy composition, fabrication variables and reinforcement level and distribution. Tests for up to 1,000 cycles were performed and the best system identified in this current work was 50v/o W/NiCrAlY. Improved resistance to thermal fatigue damage would be anticipated for specimens fabricated via optimized processing schedules. Other properties investigated included 1,093 C (2,000 F) stress rupture strength, impact resistance and static air oxidation. A composite consisting of 30v/o W-Hf-C alloy fibers in a NiCrAlY alloy matrix was shown to have a 100-hour stress rupture strength at 1,093 C (2,000 F) of 365 MN/square meters (53 ksi) or a specific strength advantage of about 3:1 over typical D.S. eutectics.

  20. Microstructure Evolution of Gas Atomized Iron Based ODS Alloys

    SciTech Connect

    Rieken, J.R.; Anderson, I.E.; Kramer, M.J.; Anderegg, J.W.; Shechtman, D.

    2009-12-01

    In a simplified process to produce precursor powders for oxide dispersion-strength- ened (ODS) alloys, gas-atomization reaction synthesis (GARS) was used to induce a surface oxide layer on molten droplets of three differing erritic stainless steel alloys during break-up and rapid solidification. The chemistry of the surface oxide was identified using auger electron spectroscopy (AES) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The precursor iron-base powders were consolidated at 850 C and 1,300 C using hot isostatic pressing (HIPing). Consolidation at the lower temperature resulted in a fully dense microstructure, while preventing substantial prior particle-boundary-oxide dissociation. Microstructural analysis of the alloys consolidated at the higher temperature confirmed a significant reduction in prior-particle-boundary-oxide volume fraction, in comparison with the lower-temperature-consolidated sample. This provided evidence that a high-temperature internal oxygen-exchange reaction occurred between the metastable prior particle-boundary-oxide phase (chromium oxide) and the yttrium contained within each prior particle. This internal oxygen-exchange reaction is shown to result in the formation of yttrium-enriched oxide dispersoids throughout the alloy microstructure. The evolving microstructure was characterized using transmission electron microscopy (TEM) and high-energy X-ray diffraction (HE-XRD).

  1. Microstructure Evolution of Gas Atomized Iron Based ODS Alloys

    SciTech Connect

    Rieken, J.R.; Anderson, I.E.; Kramer, M.J.

    2011-08-09

    In a simplified process to produce precursor powders for oxide dispersion-strengthened (ODS) alloys, gas-atomization reaction synthesis (GARS) was used to induce a surface oxide layer on molten droplets of three differing erritic stainless steel alloys during break-up and rapid solidification. The chemistry of the surface oxide was identified using auger electron spectroscopy (AES) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The precursor iron-base powders were consolidated at 850 C and 1,300 C using hot isostatic pressing (HIPing). Consolidation at the lower temperature resulted in a fully dense microstructure, while preventing substantial prior particle-boundary-oxide dissociation. Microstructural analysis of the alloys consolidated at the higher temperature confirmed a significant reduction in prior-particle-boundary-oxide volume fraction, in comparison with the lower-temperature-consolidated sample. This provided evidence that a high-temperature internal oxygen-exchange reaction occurred between the metastable prior particle-boundary-oxide phase (chromium oxide) and the yttrium contained within each prior particle. This internal oxygen-exchange reaction is shown to result in the formation of yttrium-enriched oxide dispersoids throughout the alloy microstructure. The evolving microstructure was characterized using transmission electron microscopy (TEM) and high-energy X-ray diffraction (HE-XRD).

  2. The influence of Ca-Mg-Al hydrotalcite synthesized from brine water on thermal and mechanical properties of HTlc-EVA composite

    NASA Astrophysics Data System (ADS)

    Karina, Wiwiek; Heraldy, Eddy; Pramono, Edi; Heriyanto, Astuti, Shanti

    2016-02-01

    Ca-Mg-Al hydrotalcite-like compound (Ca-Mg-Al HTlc) was prepared by co-precipitation method using brine water that is well known as the desalination process waste water. The structure of Ca-Mg-Al HTlc was determined by X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) analysis. Ca-Mg-Al HTlc was studied as a non-halogenated filler in ethylene vinyl acetate (EVA) matrix. Composites with different filler concentrations were prepared to evaluate the influence of Ca-Mg-Al HTlc on thermal and mechanical properties of EVA.The presence of Ca-Mg-Al HTlc in the composite has been confirmed by FTIR analysis. Thermal properties of composites show significant reduction of degradation temperature as well as the loading of HTlc in EVA. However, the total enthalpies combustion of composites with 1% and 5% HTlc loadings higher compared to neat EVA. Further, mechanical properties were determined by tensile test. The result shows that tensile strength and elongation at break of composites decrease relatively by Ca-Mg-Al HTlc addition.

  3. The influence of Ca-Mg-Al hydrotalcite synthesized from brine water on thermal and mechanical properties of HTlc-EVA composite

    SciTech Connect

    Karina, Wiwiek Heraldy, Eddy Pramono, Edi; Heriyanto,; Astuti, Shanti

    2016-02-08

    Ca-Mg-Al hydrotalcite-like compound (Ca-Mg-Al HTlc) was prepared by co-precipitation method using brine water that is well known as the desalination process waste water. The structure of Ca-Mg-Al HTlc was determined by X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) analysis. Ca-Mg-Al HTlc was studied as a non-halogenated filler in ethylene vinyl acetate (EVA) matrix. Composites with different filler concentrations were prepared to evaluate the influence of Ca-Mg-Al HTlc on thermal and mechanical properties of EVA.The presence of Ca-Mg-Al HTlc in the composite has been confirmed by FTIR analysis. Thermal properties of composites show significant reduction of degradation temperature as well as the loading of HTlc in EVA. However, the total enthalpies combustion of composites with 1% and 5% HTlc loadings higher compared to neat EVA. Further, mechanical properties were determined by tensile test. The result shows that tensile strength and elongation at break of composites decrease relatively by Ca-Mg-Al HTlc addition.

  4. Chemiluminescence flow biosensor for glucose using Mg-Al carbonate layered double hydroxides as catalysts and buffer solutions.

    PubMed

    Wang, Zhihua; Liu, Fang; Lu, Chao

    2012-01-01

    In this work, serving as supports in immobilizing luminol reagent, catalysts of luminol chemiluminescence (CL), and buffer solutions for the CL reaction, Mg-Al-CO(3) layered double hydroxides (LDHs) were found to trigger luminol CL in weak acid solutions (pH 5.8). The silica sol-gel with glucose oxidase and horseradish peroxidase was immobilized in the first half of the inside surface of a clear quartz tube, and luminol-hybrid Mg-Al-CO(3) LDHs were packed in the second half. Therefore, a novel CL flow-through biosensor for glucose was constructed in weak acid solutions. The CL intensity was linear with glucose concentration in the range of 0.005-1.0mM, and the detection limit for glucose (S/N=3) was 0.1 μM. The proposed biosensor exhibited excellent stability, high reproducibility and high selectivity for the determination of glucose and has been successfully applied to determine glucose in human plasma samples with satisfactory results. The success of this work has broken the bottleneck of the pH incompatibility between luminol CL and enzyme activity.

  5. The effects of cation–anion clustering on defect migration in MgAl2O4

    DOE PAGES

    Zamora, Richard J.; Voter, Arthur F.; Perez, Danny; ...

    2016-06-28

    Magnesium aluminate spinel (MgAl2O4), like many other ceramic materials, offers a range of technological applications, from nuclear reactor materials to military body armor. For many of these applications, it is critical to understand both the formation and evolution of lattice defects throughout the lifetime of the material. We use the Speculatively Parallel Temperature Accelerated Dynamics (SpecTAD) method to investigate the effects of di-vacancy and di-interstitial formation on the mobility of the component defects. From long-time trajectories of the state-to-state dynamics, we characterize the migration pathways of defect clusters, and calculate their self-diffusion constants across a range of temperatures. We findmore » that the clustering of Al and O vacancies drastically reduces the mobility of both defects, while the clustering of Mg and O vacancies completely immobilizes them. For interstitials, we find that the clustering of Mg and O defects greatly reduces O interstitial mobility, but has only a weak effect on Mg. Lastly, these findings illuminate important new details regarding defect kinetics relevant to the application of MgAl2O4 in extreme environments.« less

  6. 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.

  7. Investigating the Effects of Guest-Host Interactions on the Properties of Anion-Exchanged Mg-Al Hydrotalcites

    NASA Astrophysics Data System (ADS)

    Malherbe, François; Besse, Jean-Pierre

    2000-12-01

    A starting [Mg-Al-Cl] LDH, prepared by coprecipitation, was further anion-exchanged to incorporate a variety of anions in the interlayer domain: (Fe(CN)6)3-, (P2O7)4-, (V2O7)4-, (CrO4)2-, and (Cr2O7)2-. The resulting materials were fully characterized using classical techniques like XRPD, FTIR, TGA/DTA, and BET, and their structural modifications studied as a function of calcination temperatures. Under mild calcination, only the oxo-anions were shown to interact strongly with the host matrix. This resulted in a systematic shrinkage of the interlamellar domain, with a negative impact on the surface properties. However, intercalation of oxo-anions proved to be beneficial to thermal stability, the lamellar structure being maintained up to 400°C in the case of the dichromate intercalated [Mg-Al]. A thorough analysis of the FTIR spectra, revealing an evolution in the symmetry of some oxo-anions, confirmed the occurrence of a grafting process. Furthermore, the permanent character of the pillars was evidenced through unsuccessful rehydration and back-exchange reactions.

  8. The effects of cation-anion clustering on defect migration in MgAl2O4.

    PubMed

    Zamora, Richard J; Voter, Arthur F; Perez, Danny; Perriot, Romain; Uberuaga, Blas P

    2016-07-20

    Magnesium aluminate spinel (MgAl2O4), like many other ceramic materials, offers a range of technological applications, from nuclear reactor materials to military body armor. For many of these applications, it is critical to understand both the formation and evolution of lattice defects throughout the lifetime of the material. We use the Speculatively Parallel Temperature Accelerated Dynamics (SpecTAD) method to investigate the effects of di-vacancy and di-interstitial formation on the mobility of the component defects. From long-time trajectories of the state-to-state dynamics, we characterize the migration pathways of defect clusters, and calculate their self-diffusion constants across a range of temperatures. We find that the clustering of Al and O vacancies drastically reduces the mobility of both defects, while the clustering of Mg and O vacancies completely immobilizes them. For interstitials, we find that the clustering of Mg and O defects greatly reduces O interstitial mobility, but has only a weak effect on Mg. These findings illuminate important new details regarding defect kinetics relevant to the application of MgAl2O4 in extreme environments.

  9. Processing, properties, and applications of Ni{sub 3}Al-based alloys

    SciTech Connect

    Sikka, V.K.; Santella, M.L.; Liu, C.T.

    1997-06-01

    The Ni{sub 3}Al-based alloys represent a quantum jump in advanced alloys for structural applications at elevated temperatures. These alloys offer benefits of oxidation, carburization, and chlorination resistance, and significantly higher strength than many commercially used alloys. The commercial applications of the Ni{sub 3}Al-based alloys have begun to occur because of their comprehensive development This paper is to provide a review of. (1) alloy development, (2) melting, casting, and processing of alloys, (3) property data, (4) welding process and weldment properties, and (5) case histories of current applications. It is concluded that the cast alloy IC-221M is on its way to commercialization. 22 refs., 8 figs., 2 tabs.

  10. Kinetics and equilibrium studies on Mg-Al oxide for removal of fluoride in aqueous solution and its use in recycling.

    PubMed

    Kameda, Tomohito; Oba, Jumpei; Yoshioka, Toshiaki

    2015-06-01

    Mg-Al oxide obtained by the thermal decomposition of Mg-Al layered double hydroxide (LDH) intercalated with CO3(2-) (CO3·Mg-Al LDH) was found to take up fluoride from aqueous solution. Fluoride was removed by rehydration of Mg-Al oxide accompanied by combination with F(-). Using five times the stoichiometric quantity of Mg-Al oxide, the residual concentration of F was decreased from 100 to 6.3 mg/L in 480 min, which was below the effluent standard in Japan (8 mg/L). Removal of F(-) can be represented by pseudo-second-order reaction kinetics. The apparent rate constants at 10 °C, 30 °C, and 60 °C were 2.3 × 10(-3), 2.2 × 10(-2), and 2.5 × 10(-1) g mmol(-1) min(-1), respectively. The apparent activation energy was 73.3 kJ mol(-1). The rate-determining step for F removal by Mg-Al oxide was consistent with chemical adsorption involving intercalation of F(-) into the reconstructed Mg-Al LDH due to electrostatic attraction. The adsorption of F by Mg-Al oxide follows a Langmuir-type adsorption. The values of the maximum adsorption and the equilibrium adsorption constant were 3.0 mmol g(-1) and 1.1 × 10(3), respectively, for Mg-Al oxide. The F(-) in the F·Mg-Al LDH thus produced was found to be anion-exchanged with CO3(2-) in solution. The Mg-Al oxide after regeneration treatment had excellent properties for removal of F in aqueous solution. In conclusion, the results of this study indicated that Mg-Al oxide has potential for use in recycling to remove F in aqueous solution.

  11. Synthesis and characterization of nanostructured palladium-based alloy electrocatalysts

    NASA Astrophysics Data System (ADS)

    Sarkar, Arindam

    Low temperature fuel cells like proton exchange membrane fuel cells (PEMFC) are expected to play a crucial role in the future hydrogen economy, especially for transportation applications. These electrochemical devices offer significantly higher efficiency compared to conventional heat engines. However, use of exotic and expensive platinum as the electrocatalyst poses serious problems for commercial viability. In this regard, there is an urgent need to develop low-platinum or non-platinum electrocatalysts with electrocatalytic activity for the oxygen reduction reaction (ORR) superior or comparable to that of platinum. This dissertation first investigates non-platinum, palladium-based alloy electrocatalysts for ORR. Particularly, Pd-M (M = Mo and W) alloys are synthesized by a novel thermal decomposition of organo-metallic precursors. The carbon-supported Pd-M (M = Mo, W) electrocatalyts are then heat treated up to 900°C in H2 atmosphere and investigated for their phase behavior. Cyclic voltammetry (CV) and rotating disk electrode (RDE) measurements reveal that the alloying of Pd with Mo or W significantly enhances the catalytic activity for ORR as well as the stability (durability) of the electrocatalysts. Additionally, both the alloy systems exhibit high tolerance to methanol, which is particularly advantageous for direct methanol fuel cells (DMFC). The dissertation then focuses on one-pot synthesis of carbon-supported multi-metallic Pt-Pd-Co nanoalloys by a rapid microwave-assisted solvothermal (MW-ST) method. The multi-metallic alloy compositions synthesized by the MW-ST method show much higher catalytic activity for ORR compared to their counterparts synthesized by the conventional borohydride reduction method. Additionally, a series of Pt encapsulated Pd-Co nanoparticle electrocatalysts are synthesized by the MW-ST method and characterized to understand their phase behavior, surface composition, and electrocatalytic activity for ORR. Finally, the dissertation

  12. Dendritic growth and structure of undercooled nickel base alloys

    NASA Technical Reports Server (NTRS)

    Flemings, M. C.; Shiohara, Y.

    1988-01-01

    The principal objectives of this overall investigation are to: study means for obtaining high undercooling in levitation melted droplets, and study structures produced upon the solidification of these undercooled specimens. Thermal measurements are made of the undercooling, and of the rapid recalescence, to develop an understanding of the solidification mechanism. Comparison of results is made with the modeling studies. Characterization and metallographic work is done to gain an understanding of the relationship between rapid solidification variables and the structures so produced. In ground based work to date, solidification of undercooled Ni-25 wt percent Sn alloy was observed by high-speed cinematography and the results compared with optical temperature measurements. Also in ground based work, high-speed optical temperature measurements were made of the solidification behavior of levitated metal samples within a transparent glass medium. Two undercooled Ni-Sn alloys were examined. Measurements were carried out on samples at undercoolings up to 330 K. Microstructures of samples produced in ground based work were determined by optical metallography and by SEM, and microsegregation by electron microprobe measurements. A series of flight tests were planned to conduct experiments similar to the ground based experiments. The Space Shuttle Columbia carried an alloy undercooled experiment in the STS 61-C mission in January 1986. A sample of Ni-32.5 wt percent Sn eutectic was melted and solidified under microgravity conditions.

  13. Cr{sub 2}Nb-based alloy development

    SciTech Connect

    Liu, C.T.; Tortorelli, P.F.; Horton, J.A.

    1995-06-01

    The objective of this task is to develop a new generation of structural materials based on intermetallic alloys for use as critical hot components in advanced fossil energy conversion systems. The intermetallic phase, Cr{sub 2}Nb, with a complex cubic structure (C-15) has been selected for this development because of its high melting point (1770{degrees}C), relatively low material density (7.7 g/cm{sup 2}), excellent high-temperature strength (at 1000 to 1250{degrees}C), and potential resistance to oxidation and corrosion. This intermetallic phase, like many other Laves phases, has a wide range of compositional homogeneity suggesting the possibility of improving its mechanical and metallurgical properties by alloying additions. The major engineering concern with Cr{sub 2}Nb and other A{sub 2}B Laves phases is their poor fracture toughness and fracture resistance at ambient temperatures. The single-phase Cr{sub 2}Nb is very hard ({approximately}800 DPH) and brittle at room temperature. Because of this brittleness, the development effort has concentrated on two-phase structures containing the hard intermetallic phase Cr{sub 2}Nb and the softer Cr-rich solid solution phase. Potential applications of Cr-Cr{sub 2}Nb alloys include hot components (for example, air heat exchangers and turbine blades) in advanced energy conversion systems and heat engines, wear-resistant parts in coal handling systems (e.g., nozzles), drill bits for oil/gas wells, and valve guides in diesel engines. Current studies are focuses on enhancement of fracture resistance in tension at ambient temperatures and oxidation resistance above 1000{degrees}C. This report summarizes recent progress on controlling microstructure and improving the mechanical and metallurgical properties and the high-temperature corrosion behavior of Cr-Cr{sub 2}Nb alloys through alloying conditions, material processing, and heat treatment.

  14. Microscopic study of the structure of the Steel Ni-based Alloy: Hastelloy G35 Alloy

    NASA Astrophysics Data System (ADS)

    Sabir, F.; Ben Lenda, O.; Saissi, S.; Marbouh, K.; Tyouke, B.; Zerrouk, L.; Ibnlfassi, A.; Ouzaouit, K.; Elmadani, S.

    2017-03-01

    The study of the influence of heat treatment on changes of mechanical and structural properties of Steel Ni-based Alloy is a highly interdisciplinary topic at the interface of the physical chemistry of metallic materials, which also helps in environmental and economic protection.After heat treatment, the structural and micro-structural studies for the different transformation temperature led to identify phases formed and the morphology. This work has been carried out using different techniques: X-ray diffraction, optical microscopy and scanning electron microscopy.

  15. Investigation on the primary creep of a nickel based alloy. [Nimonic 75 type alloy

    SciTech Connect

    Kong, Q.P.; Wang, X. )

    1993-07-01

    It is widely accepted that dislocation climb is involved in the steady state (i.e. secondary) creep at high temperatures, which is characterized by the formation and evolution of substructures. In current theories of steady state creep, dislocation climb is regarded as the rate controlling process. However, the role of dislocation climb in the primary (i.e. transient) creep at high temperatures is not clear. The present paper is to report the observations by transmission electron microscopy (TEM) on high temperature creep of a nickel based alloy. It will be shown that dislocation climb plays an important role not only in the steady state creep, but also in the primary creep.

  16. Predictive Guide for Collective CO2 Adsorption Properties of Mg-Al Mixed Oxides.

    PubMed

    Kwon, Hyuk Jae; Kwon, Soonchul; Seo, Jeong Gil; Jung, In Sun; Son, You-Hwan; Lee, Chan Hyun; Lee, Ki Bong; Lee, Hyun Chul

    2017-04-22

    Although solid adsorption processes offer attractive benefits, such as reduced energy demands and penalties compared with liquid absorption processes, there are still pressing needs for solid adsorbents with high adsorption capacities, thermal efficiencies, and energy-intensive regeneration in gas-treatment processes. The CO2 adsorption capacities of layered double oxides (LDOs), which are attractive solid adsorbents, have an asymmetric volcano-type correlation with their relative crystallinities. Furthermore, new collective adsorption properties (adsorption capacity, adsorptive energy and charge-transfer amount based on the adsorbent weight) are proposed based on density functional theory (DFT) calculations and measured surface areas. The correlation of these collective properties with their crystallinities is in good agreement with the experimentally measured CO2 adsorptive capacity trend, providing a predictive guide for the development of solid adsorbents for gas-adsorption processes. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Polarization-corrosion behavior of commercial gold- and silver-base casting alloys in Fusayama solution.

    PubMed

    Johnson, D L; Rinne, V W; Bleich, L L

    1983-12-01

    Based on polarization measurements, high Au alloys are highly corrosion-resistant and exhibit the lowest corrosion rates; intermediate Au, Ag, and Pd alloys with Cu are passive but exhibit higher corrosion rates. Twenty weight percent (w/o) In-Ag alloys exhibit active corrosion behavior at potentials only 100 mV noble to the corrosion potential.

  18. An investigation of the initiation stage of hot corrosion in Ni-base alloys

    NASA Technical Reports Server (NTRS)

    Huang, T. T.; Meier, G. H.

    1979-01-01

    The commercial nickel base alloy, IN-738, and high purity laboratory alloys were prepared to simulate the effects of the major elements in IN-738. Results indicate that the initiation of hot corrosion attack of IN-738 and other similar alloys is the result of local penetration of molten salt through the protective oxide scale.

  19. Iron-based alloys with corrosion resistance to oxygen-sulfur mixed gases

    DOEpatents

    Natesan, K.

    1992-11-17

    An iron-based alloy with improved performance with exposure to oxygen-sulfur mixed gases with the alloy containing about 9--30 wt. % Cr and a small amount of Nb and/or Zr implanted on the surface of the alloy to diffuse a depth into the surface portion, with the alloy exhibiting corrosion resistance to the corrosive gases without bulk addition of Nb and/or Zr and without heat treatment at temperatures of 1000--1100 C. 7 figs.

  20. Iron-based alloys with corrosion resistance to oxygen-sulfur mixed gases

    DOEpatents

    Natesan, Krishnamurti

    1992-01-01

    An iron-based alloy with improved performance with exposure to oxygen-sulfur mixed gases with the alloy containing about 9-30 wt. % Cr and a small amount of Nb and/or Zr implanted on the surface of the alloy to diffuse a depth into the surface portion, with the alloy exhibiting corrosion resistance to the corrosive gases without bulk addition of Nb and/or Zr and without heat treatment at temperatures of 1000.degree.-1100.degree. C.

  1. Combined thermodynamic study of nickel-base alloys. Progress report

    SciTech Connect

    Brooks, C. R.; Meschter, P. J.

    1981-02-15

    Achievements during this period are the following: (1) initiation of a high-temperature study of the Ni-Ta system using the galvanic cell technique, (2) emf study of high-temperature thermodynamics in the Ni-Mo system, (3) measured heat capacity data on ordered and disordered Ni/sub 4/Mo, (4) heat capacities of Ni and disordered Ni/sub 3/Fe, and (5) computer correlation of thermodynamic and phase diagram data in binary Ni-base alloys. (MOW)

  2. Attack polish for nickel-base alloys and stainless steels

    DOEpatents

    Not Available

    1980-05-28

    A chemical attack polish and polishing procedure for use on metal surfaces such as nickel base alloys and stainless steels is described. The chemical attack polich comprises FeNO/sub 3/, concentrated CH/sub 3/COOH, concentrated H/sub 2/SO/sub 4/ and H/sub 2/O. The polishing procedure includes saturating a polishing cloth with the chemical attack polish and submicron abrasive particles and buffing the metal surface.

  3. Attack polish for nickel-base alloys and stainless steels

    DOEpatents

    Steeves, Arthur F.; Buono, Donald P.

    1983-01-01

    A chemical attack polish and polishing procedure for use on metal surfaces such as nickel base alloys and stainless steels. The chemical attack polish comprises Fe(NO.sub.3).sub.3, concentrated CH.sub.3 COOH, concentrated H.sub.2 SO.sub.4 and H.sub.2 O. The polishing procedure includes saturating a polishing cloth with the chemical attack polish and submicron abrasive particles and buffing the metal surface.

  4. Method of polishing nickel-base alloys and stainless steels

    DOEpatents

    Steeves, Arthur F.; Buono, Donald P.

    1981-01-01

    A chemical attack polish and polishing procedure for use on metal surfaces such as nickel base alloys and stainless steels. The chemical attack polish comprises Fe(NO.sub.3).sub.3, concentrated CH.sub.3 COOH, concentrated H.sub.2 SO.sub.4 and H.sub.2 O. The polishing procedure includes saturating a polishing cloth with the chemical attack polish and submicron abrasive particles and buffing the metal surface.

  5. Resistance of a directionally solidified gamma/gamma prime-delta eutectic alloy to recrystallization. [Ni-base alloy

    NASA Technical Reports Server (NTRS)

    Tewari, S. N.; Scheuermann, C. M.; Andrews, C. W.

    1976-01-01

    A lamellar nickel-base directionally-solidified eutectic gamma/gamma prime-delta alloy has potential as an advanced gas turbine blade material. The microstructural stability of this alloy was investigated. Specimens were plastically deformed by uniform compression or Brinell indentation, then annealed between 750 and 1120 C. Microstructural changes observed after annealing included gamma prime coarsening, pinch-off and spheroidization of delta lamellae, and appearance of an unidentified blocky phase in surface layers. All but the first of these was localized in severely deformed regions, suggesting that microstructural instability may not be a serious problem in the use of this alloy.

  6. Stacking of lamellae in Mg/Al hydrotalcites: Effect of metal ion concentrations on morphology

    SciTech Connect

    Panda, H.S.; Srivastava, R.; Bahadur, D.

    2008-06-03

    A hybrid nanocomposite based on the intercalation of carbonate anion has been synthesized through co-precipitation technique. Powder X-ray diffraction patterns (PXRD) showed pure layered double hydroxide (LDH) phases having crystallite size around 20 and 13 nm in 'a' and 'c' crystallographic directions, respectively. Fourier transform infrared and Raman spectroscopy measurements exhibit shifting of bands with increase of divalent metal ion concentration and it further suggests the presence of carbonate anions. Differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA) exhibit the three stages of thermal degradation, which is characteristic behaviour of layered double hydroxide. CHN and energy dispersive X-ray analysis support the PXRD and spectroscopy results. The nature of charge observed through Zeta potential analyzer is positive. Transmission electron microscope (TEM) exhibits the characteristic LDH platelet morphology with the platelets stacked one above the other.

  7. Fabrication of Al/Mg/Al Composites via Accumulative Roll Bonding and Their Mechanical Properties

    PubMed Central

    Nie, Jinfeng; Liu, Mingxing; Wang, Fang; Zhao, Yonghao; Li, Yusheng; Cao, Yang; Zhu, Yuntian

    2016-01-01

    Al(1060)/Mg(AZ31)/Al(1060) multilayered composite was successfully produced using an accumulative roll bonding (ARB) process for up to four cycles at an elevated temperature (400 °C). The microstructure evolution of the composites and the bonding characteristics at the interfaces between Al and Mg layers with increasing ARB cycles were characterized through optical microscopy, field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). It was found that the grains of Al and Mg layers were significantly refined and Al3Mg2 and Al12 Mg17 intermetallic compound layers formed at the Al/Mg bonding interfaces. The strength increased gradually and the ultimate tensile strength (UTS) reached a maximum value of about 240 MPa at the third pass. Furthermore, the strengthening mechanism of the composite was analyzed based on the fracture morphologies. PMID:28774072

  8. Preparation of Mg-Al layered double hydroxide intercalated with Coomassie Brilliant Blue R anion and its uptake of aromatic compounds from aqueous solutions.

    PubMed

    Kameda, Tomohito; Sato, Syunsuke; Yoshioka, Toshiaki

    2012-01-01

    The objective of this study is to evaluate the capacity of Mg-Al layered double hydroxide (Mg-Al LDH) intercalated with organic dye to adsorb aromatic compounds in aqueous solutions. Mg-Al LDH intercalated with Coomassie Brilliant Blue R anion (BB(-)) was prepared by coprecipitation. The BB(-)-intercalated Mg-Al LDH was able to adsorb aromatic compounds from an aqueous solution, despite the electron density in the benzene ring of the aromatics. This uptake is caused by π-π stacking interactions, either between the electron-rich benzene rings of intercalated BB(-) and the benzene rings of aromatics with a low electron density or between the electron-poor benzene rings of intercalated BB(-) and the benzene rings of the aromatics with a high electron density.

  9. Wear resistant zirconium base alloy article for water reactors

    SciTech Connect

    Gillett, J.E.; Shockling, L.A.; Sherwood, D.G.

    1988-03-01

    In a water reactor operating environment, the combination having improved fretting wear resistance is described comprising: an elongated tubular water displacer rod; having a low neutron absorption cross section guide support plates distributed along the length of the water displacer rod; the water displacer rod intersecting the guide support plates through apertures in the guide support plates; the water displacer rod having a plurality of spaced apart annular electrospark deposited coatings, each coating facing the wall of a respective aperture, the electrospark deposited coatings comprising Cr/sub 2/C/sub 3/; wherein the water displacer rod has a tube wall composed of a zirconium base alloy; and wherein the guide support plates are composed of a stainless steel alloy.

  10. DEVELOPMENT OF PROTECTIVE COATING FOR TANTALUM BASE ALLOYS.

    DTIC Science & Technology

    TANTALUM ALLOYS, PROTECTIVE TREATMENTS), (*REFRACTORY COATINGS , SILICIDES ), TUNGSTEN ALLOYS, OXIDATION, OXIDES, OXYGEN, DIFFUSION, HIGH TEMPERATURE...HAFNIUM COMPOUNDS, ZIRCONIUM COMPOUNDS, NIOBIUM ALLOYS, VANADIUM ALLOYS, THERMAL EXPANSION, THERMAL STRESSES, MICROSTRUCTURE, YTTRIUM COMPOUNDS...TANTALUM COMPOUNDS, ADDITIVES, ALUMINUM, BORON, CHROMIUM, MANGANESE, MOLYBDENUM, TITANIUM, TUNGSTEN, VANADIUM, NIOBIUM , SODIUM COMPOUNDS, FLUORIDES, SILICON

  11. Synthesis and characterization of nanocrystalline MgAl{sub 2}O{sub 4} spinel via sucrose process

    SciTech Connect

    Alinejad, Babak Sarpoolaky, Hosein; Beitollahi, Ali; Saberi, Ali; Afshar, Shahrara

    2008-05-06

    Nanocrystalline MgAl{sub 2}O{sub 4} spinel powder was synthesized using metal nitrates and a polymer matrix precursor composed of sucrose and polyvinyl alcohol (PVA). The precursor and the calcined powders were characterized by simultaneous thermal analysis (STA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). According to XRD results, the inceptive formation temperature of spinel via this technique was between 600 and 700 deg. C. The calcined powder at 800 deg. C for 2 h has faced shaped morphology and its crystallite size is in the range of 8-12 nm. Further studies also showed that the amount of polymeric matrix to metal ions has significant influence on the crystallite size of synthesized magnesium aluminate spinel powder.

  12. Low keV electron probe analysis of silicate minerals for Mg, Al, and Si using pure-element standards

    NASA Technical Reports Server (NTRS)

    Cunningham, G. G.

    1972-01-01

    Accurate electron probe values for Mg, Al, and Si in silicate minerals may be obtained with pure-element standards. Analysis must be done at low (6 kV) accelerating potential and for best results, the average atomic number of the sample should be within about plus or minus 1 of the atomic number of the pure-element standard. This last requirement is automatically fulfilled for most common silicate minerals, as their average atomic numbers usually fall within the 11 to 15 range. Examples studied include a wet-chemically analyzed cordierite containing 17.71 weight percent Al, for which a value of 17.6 plus or minus 0.3 percent was obtained with the electron probe, and a hornblende containing 19.15 percent Si, which gave 19.0 plus or minus 0.3 percent using the probe method.

  13. Exchange of interlayer terephthalate anions from a Mg Al layered double hydroxide: formation of intermediate interstratified phases

    NASA Astrophysics Data System (ADS)

    Kaneyoshi, Masami; Jones, William

    1998-10-01

    The exchange of interlayer terephthalate (TA) anions from a Mg-Al layered double hydroxide (LDH) by carbonate, sulfate, chloride and nitrate anions is reported. It is shown that TA is readily exchanged by CO 32- and SO 42- but only partly by Cl - and NO 3-. We demonstrate that during the exchange process interstratified phases are observed. Such interstratification has previously been reported only for directly synthesised materials. The origin of the interstratification is believed to be associated with two preferred orientations of TA anions within the layers, i.e. vertical or horizontal to the clay sheets. Two models for the possible exchange mechanism which is operating in these systems are proposed.

  14. Role of alloying elements in adhesive transfer and friction of copper-base alloys

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.

    1978-01-01

    Sliding friction experiments were conducted in a vacuum with binary-copper alloy riders sliding against a conventional bearing-steel surface with normal residual oxides present. The binary alloys contained 1 atomic percent of various alloying elements. Auger spectroscopy analysis was used to monitor the adhesive transfer of the copper alloys to the bearing-steel surface. A relation was found to exist between adhesive transfer and the reaction potential and free energy of formation of the alloying element in the copper. The more chemically active the element and the more stable its oxide, the greater was the adhesive transfer and wear of the copper alloy. Transfer occurred in all the alloys except copper-gold after relatively few (25) passes across the steel surface.

  15. Effect of cutting edge radius on surface roughness in diamond tool turning of transparent MgAl2O4 spinel ceramic

    NASA Astrophysics Data System (ADS)

    Yue, Xiaobin; Xu, Min; Du, Wenhao; Chu, Chong

    2017-09-01

    Transparent magnesium aluminate spinel (MgAl2O4) ceramic is one of an important optical materials. However, due to its pronounced hardness and brittleness, the optical machining of this material is very difficult. Diamond turning has advantages over the grinding process in flexibility and material removal rate. However, there is a lack of research that could support the use of diamond turning technology in the machining of MgAl2O4 spinel ceramic. Using brittle-ductile transition theory of brittle material machining, this work provides critical information that may help to realize ductile-regime turning of MgAl2O4 spinel ceramic. A characterization method of determination the cutting edge radius is introduced here. Suitable diamond tools were measured for sharpness and then chosen from a large number of candidate tools. The influence of rounded cutting edges on surface roughness of the MgAl2O4 spinel ceramic is also investigated. These results indicate that surface quality of MgAl2O4 spinel is relate to the radius of diamond tool's cutting edge, cutting speed, and feed rate. Sharp diamond tools (small radius of cutting edge) facilitated ductile-regime turning of MgAl2O4 spinel and shows great potential to reduce surface roughness and produce smoother final surface.

  16. Enhanced photocatalytic properties of the 3D flower-like Mg-Al layered double hydroxides decorated with Ag{sub 2}CO{sub 3} under visible light illumination

    SciTech Connect

    Ao, Yanhui Wang, Dandan; Wang, Peifang; Wang, Chao; Hou, Jun; Qian, Jin

    2016-08-15

    Highlights: • 3D flower-like Ag{sub 2}CO{sub 3}/Mg-Al layered double hydroxide composite was prepared. • The nanocomposites exhibited high photocatalytic activities on different organic pollutants. • The mechanism of the enhanced activity were investigated. - Abstract: A facile anion-exchange precipitation method was employed to synthesize 3D flower-like Ag{sub 2}CO{sub 3}/Mg-Al layered double hydroxide composite photocatalyst. Results showed that Ag{sub 2}CO{sub 3} nanoparticles dispersed uniformly on the petals of the flower-like Mg-Al LDH. The obtained nanocomposites exhibited high photocatalytic activities on different organic pollutants (cationic and anionic dyes, phenol) under visible light illumination. The high photocatalytic activity can be ascribed to the special structure which accomplishes the wide-distribution of Ag{sub 2}CO{sub 3} nanoparticles on the surfaces of the 3D flower-like nanocomposites. Therefore, it can provide much more active sites for the degradation of organic pollutant. Then the photocatalytic mechanism was also verified by reactive species trapping experiments in detail. The work would pave a facile way to prepare LDHs based hierarchical photocatalysts with high activity for the degradation of wide range organic pollutants under visible light irradiation.

  17. Pack cementation diffusion coatings for iron-base alloys

    SciTech Connect

    Rapp, R.A.

    1995-02-01

    With the aid of computer-assisted calculations of the equilibrium vapor pressures in halide-activated cementation packs, processing conditions have been identified and experimentally verified for the codeposition of two or more alloying elements in a diffusion coating on a variety of steels. The Cr-Si ferrite layers have proven to be very resistant to high temperature cyclic oxidation and to pitting in aqueous solutions. The process has been patented, and is being transferred for industrial application, e.g. for water walls of utility boilers, etc. In the proposed extension of this project, the use of mixed pure metal powders in the pack will be extended to achieve similar ferrite Fe-Cr-Al coatings with excellent oxidation resistance, with the eventual transfer of the technology to industry. In other recent studies, Ni-base alloy rods were aluminized by the halide-activated pack cementation process to bring their average composition to that for the ORNL-developed Ni{sub 3}Al, for use as a welding rod. A similar effort to develop a welding rod for the ORNL Fe{sub 3}Al alloy did not yield reproducible coating compositions or growth kinetics. The continued effort to produce Duriron-type (Fe-18Si-5Cr) coatings on steels was not successful. Literature for the intrinsic diffusion coefficients suggests that this task cannot be achieved.

  18. Characterization of Mg/Al butt joints welded by gas tungsten arc filling with Zn–29.5Al–0.5Ti filler metal

    SciTech Connect

    Liu, Fei; Wang, Hongyang; Liu, Liming

    2014-04-01

    The multivariate alloying design of a welding joint is used in the Mg to Al welding process. A Zn–29.5Al–0.5Ti alloy is added as filler metal in gas tungsten arc welding of Mg and Al alloy joint based on the analysis of Al and Mg alloy characteristics. The tensile strength, microstructure, and phase constitution of the weld seam are analyzed. The formation of brittle and hard Mg–Al intermetallic compounds is avoided because of the effects of Zn, Al, and Ti. The average tensile strength of the joint is 148 MPa. Al{sub 3}Ti is first precipitated and functions as the nucleus of heterogeneous nucleation during solidification. Moreover, the precipitated Al–MgZn{sub 2} hypoeutectic phase exhibited a feather-like structure, which enhances the property of the Mg–Al dissimilar joint. - Highlights: • Mg alloy AZ31B and Al alloy 6061 are butt welded by fusion welding. • The effect of Ti in filler metal is investigated. • The formation of Mg–Al intermetallic compounds is avoided.

  19. Mechanical Properties and Fracture Behaviors of the As-Extruded Mg-5Al-3Ca Alloys Containing Yttrium at Elevated Temperature.

    PubMed

    Son, Hyeon-Taek; Kim, Yong-Ho; Kim, Taek-Soo; Lee, Seong-Hee

    2016-02-01

    Effects of yttrium (Y) addition on mechanical properties and fracture behaviors of the as-extruded Mg-Al-Ca based alloys at elevated temperature were investigated by a tensile test. After hot extrusion, the average grain size was refined by Y addition and eutectic phases were broken down into fine particles. Y addition to Mg-5Al-3Ca based alloy resulted in the improvement of strength and ductility at elevated temperature due to fine grain and suppression of grain growth by formation of thermally stable Al2Y intermetallic compound.

  20. Compressive creep behavior of alloys based on B2 FeAl

    NASA Technical Reports Server (NTRS)

    Mantravadi, N.; Vedula, K.; Gaydosh, D.; Titran, R. H.

    1987-01-01

    Alloys based on FeAl are attractive alternative materials for environmental resistance at intermediate temperatures. Addition of small amounts of Nb, Hf, Ta, Mo, Zr, and B were shown to improve the compressive creep of this alloy at 1100 K. Boron, in particular, was found to have a synergistic effect along with Zr in providing properties substantially better than the binary alloy. This improvement seems to be related to the higher activation energy found for this alloy, suggesting a modification in the diffusion behavior due to the alloying additions.

  1. Thermogravimetric study of reduction of oxides present in oxidized nickel-base alloy powders

    NASA Technical Reports Server (NTRS)

    Herbell, T. P.

    1976-01-01

    Carbon, hydrogen, and hydrogen plus carbon reduction of three oxidized nickel-base alloy powders (a solid solution strengthened alloy both with and without the gamma prime formers aluminum and titanium and the solid solution strengthened alloy NiCrAlY) were evaluated by thermogravimetry. Hydrogen and hydrogen plus carbon were completely effective in reducing an alloy containing chromium, columbium, tantalum, molybdenum, and tungsten. However, with aluminum and titanium present the reduction was limited to a weight loss of about 81 percent. Carbon alone was not effective in reducing any of the alloys, and none of the reducing conditions were effective for use with NiCrAlY.

  2. Compressive creep behavior of alloys based on B2 FeAl

    NASA Technical Reports Server (NTRS)

    Mantravadi, N.; Vedula, K.; Gaydosh, D.; Titran, R. H.

    1986-01-01

    Alloys based on FeAl are attractive alternate materials for environmental resistance at intermediate temperatures. Addition of small amounts of Nb, Hf, Ta, Mo, Zr, and B were shown to improve the compressive creep of this alloy at 1100 K. Boron, in particular, was found to have a synergistic effect along with Zr in providing properties substantially better than the binary alloy. This improvement seems to be related to the higher activation energy found for this alloy, suggesting a modification in the diffusion behavior due to the alloying additions.

  3. On the corrosion behavior and biocompatibility of palladium-based dental alloys

    NASA Astrophysics Data System (ADS)

    Sun, Desheng

    Palladium-based alloys have been used as dental restorative materials for about two decades with good clinical history. But there have been clinical case reports showing possible allergy effects from these alloys. The aim of this study was to characterize the corrosion behavior and mechanisms of several palladium-based dental alloys by potentiodynamic polarization methods, electrochemical impedance spectroscopy (EIS), and scanning Kelvin probe force microscopy/atomic force microscopy (SKPFM/AFM), and to evaluate their biocompatibility by a cell culture technique and an animal model. Using SKPFM/AFM and scanning electron microscopy, the Ru-enriched phase from the use of ruthenium as a grain-refining element was identified as being slightly more noble than the palladium solid solution matrix in a high-palladium alloy. Other secondary precipitates that exist in the microstructures of these high-palladium alloys have minimal differences in Volta potential compared to the matrix. For high-palladium alloys, corrosion is generally uniform due to the predominant palladium content in the different phases. Potentiodynamic polarization and EIS have shown that representative palladium-silver alloys have low corrosion tendency and high corrosion resistance, which are equivalent to a well-known high-noble gold-palladium alloy in simulated body fluid and oral environments. The palladium-silver alloys tested are resistant to chloride ion corrosion. Passivation and dealloying have been identified for all of the tested palladium-silver alloys. The great similarity in corrosion behavior among the palladium-silver alloys is attributed to their similar chemical compositions. The variation in microstructures of palladium-silver alloys tested does not cause significant difference in corrosion behavior. The corrosion resistance of these palladium-silver alloys at elevated potentials relevant to oral environment is still satisfactory. The release of elements from representative dental

  4. Rare-earth metals in nickel aluminide-based alloys: III. Structure and properties of multicomponent Ni3Al-based alloys

    NASA Astrophysics Data System (ADS)

    Bazyleva, O. A.; Povarova, K. B.; Kazanskaya, N. K.; Drozdov, A. A.

    2009-04-01

    The possibility of increasing the life of heterophase cast light Ni3Al-based superalloys at temperatures higher than 0.8 T m of Ni3Al is studied when their directional structure is additionally stabilized by nanoprecipitates, which form upon additional alloying of these alloys by refractory and active metals, and using special methods for preparing and melting of an alloy charge. The effect of the method of introducing the main components and refractory reaction-active and surface-active alloying elements into Ni3Al-based cast superalloys, which are thermally stable natural composite materials of the eutectic type, on the structure-phase state and the life of these alloys is studied. When these alloys are melted, it is necessary to perform a set of measures to form particles of refractory oxide cores covered with the β-NiAl phase and, then, γ'prim-Ni3Al phase precipitates during solidification. The latter phase forms the outer shell of grain nuclei, which provides high thermal stability and hot strength of an intermetallic compound-based alloy. As a result, a modified structure that is stabilized by the nanoprecipitates of nickel and aluminum lanthanides and the nanoprecipitates of phases containing refractory metals is formed. This structure enhances the life of the alloy at 1000 °C by a factor of 1.8-2.5.

  5. Crystallization kinetics of Fe based amorphous alloy

    NASA Astrophysics Data System (ADS)

    Shanker Rao, T.; Lilly Shanker Rao, T.

    2015-02-01

    Differential Scanning Calorimetry(DSC) experimental data under non-isothermal conditions for Fe based Metglas 2605SA1 (wt% Fe=85-95, Si=5-10, B=1-5) metallic glass ribbons are reported and discussed. The DSC Scans performed at different heating rates showed two step crystallization processes and are interpreted in terms of different models like Kissinger, Ozawa, Boswell, Augis & Bennett and Gao & Wang. From the heating rate dependence of the onset temperature (To) and the crystallization peak temperature (Tp), the kinetic triplet, activation energy of crystallization (E), Avrami exponent (n) and the frequency factor (A) are determined. The determined E for peak I is 354.5 ± 2.5 kJ/mol and for the peak II is 348.2 ± 2.2 kJ/mol, respectively. The frequency factor for peak I is 1.1 × 1023sec-1 and for peak II is 6.1 × 1020sec-1.

  6. Effects of thermal aging on microstructures of low alloy steel-Ni base alloy dissimilar metal weld interfaces

    NASA Astrophysics Data System (ADS)

    Choi, Kyoung Joon; Kim, Jong Jin; Lee, Bong Ho; Bahn, Chi Bum; Kim, Ji Hyun

    2013-10-01

    In this study, the advanced instrumental analysis has been performed to investigate the effect of long-term thermal aging on the microstructural evolution in the fusion boundary region between weld metal and low alloy steel in dissimilar metal welds. A representative dissimilar weld mock-up made of Alloy 690-Alloy 152-A533 Gr. B was fabricated and aged at 450 °C for 2750 h. The micro- and nano-scale characterization were conducted mainly near in a weld root region by using optical microscopy, scanning electron microscopy, transmission electron microscopy, and three dimensional atom probe tomography. It was observed that the weld root was generally divided into several regions including dilution zone in the Ni-base alloy weld metal, fusion boundary, and heat-affected zone in the low alloy steel. A steep gradient was shown in the chemical composition profile across the interface between A533 Gr. B and Alloy 152. The precipitation of carbides was also observed along and near the fusion boundary of as-welded and aged dissimilar metal joints. It was also found that the precipitation of Cr carbides was enhanced by the thermal aging near the fusion boundary.

  7. Investigation on corrosion and wear behaviors of nanoparticles reinforced Ni-based composite alloying layer

    NASA Astrophysics Data System (ADS)

    Xu, Jiang; Tao, Jie; Jiang, Shuyun; Xu, Zhong

    2008-04-01

    In order to investigate the role of amorphous SiO 2 particles in corrosion and wear resistance of Ni-based metal matrix composite alloying layer, the amorphous nano-SiO 2 particles reinforced Ni-based composite alloying layer has been prepared by double glow plasma alloying on AISI 316L stainless steel surface, where Ni/amorphous nano-SiO 2 was firstly predeposited by brush plating. The composition and microstructure of the nano-SiO 2 particles reinforced Ni-based composite alloying layer were analyzed by using SEM, TEM and XRD. The results indicated that the composite alloying layer consisted of γ-phase and amorphous nano-SiO 2 particles, and under alloying temperature (1000 °C) condition, the nano-SiO 2 particles were uniformly distributed in the alloying layer and still kept the amorphous structure. The corrosion resistance of composite alloying layer was investigated by an electrochemical method in 3.5%NaCl solution. Compared with single alloying layer, the amorphous nano-SiO 2 particles slightly decreased the corrosion resistance of the Ni-Cr-Mo-Cu alloying layer. X-ray photoelectron spectroscopy (XPS) revealed that the passive films formed on the composite alloying consisted of Cr 2O 3, MoO 3, SiO 2 and metallic Ni and Mo. The dry wear test results showed that the composite alloying layer had excellent friction-reduced property, and the wear weight loss of composite alloying layer was less than 60% of that of Ni-Cr-Mo-Cu alloying layer.

  8. The Structure and Properties of Rapid Cooled Iron Based Alloy

    NASA Astrophysics Data System (ADS)

    Jeż, B.; Nabialek, M.; Pietrusiewicz, P.; Gruszka, K.; Błoch, K.; Gondro, J.; Rzącki, J.; Abdullah, M. M. A. B.; Sandu, A. V.; Szota, M.; Jeż, K.; Sałagacki, A.

    2017-06-01

    In this paper we studied the structure of rapidly cooled alloy which composition was based on iron. Samples were prepared using arc melting under protective atmosphere of argon and then casted in the process of rapid cooling into water cooled copper mold. Samples of the same composition were also made using the liquid melt casting method on a spinning copper roll. The high purity samples in the form of rods and ribbons were obtained. As expected, the obtained samples were characterized by an amorphous structure as confirmed by Mössbauer spectroscopy and X-ray diffraction studies.

  9. Structure of hydrides based on V-Cr alloys

    NASA Astrophysics Data System (ADS)

    Lushnikov, S. A.; Verbetskii, V. N.; Somenkov, V. A.; Glazkov, V. P.

    2014-11-01

    The structure of deuterides based on V0.9Cr0.1 and V0.5Cr0.5 alloys has been investigated by neutron diffraction at room and low (77 K) temperatures. It is found that V0.9Cr0.1D2.0 deuteride has a CaF2 ( Fm3 m) crystal structure, which corresponds to vanadium dihydride. V0.5Cr0.5D0.7 deuteride has a NiAs ( P6/3 mmc) structure type, similar to chromium hydride.

  10. DENSITY-FUNCTIONAL STUDY OF Zr-BASED ACTINIDE ALLOYS

    SciTech Connect

    Landa, A; Soderlind, P; Turchi, P; Vitos, L; Ruban, A

    2008-06-26

    Density-functional formalism is applied to study the phase equilibria in the U-Zr system. The obtained ground-state properties of the {gamma} (bcc) and {delta} (C32) phases are in good agreement with experimental data. The decomposition curve for the {gamma}-based U-Zr solutions is calculated. We argue that stabilization of the {delta}-UZr{sub 2} phase relative to the {alpha}-Zr (hcp) structure is due to an increase of the Zr d-band occupancy that occurs when U is alloyed with Zr.

  11. Adhesion, friction and Auger spectroscopy analysis of a commercial cobalt base aircraft turbine shroud alloy

    NASA Technical Reports Server (NTRS)

    Buckley, D. H.

    1974-01-01

    A commercially used cast cobalt base alloy was investigated as a turbine shroud material which revealed a surface enriched with tungsten and carbon suggesting a surface layer of tungsten carbide. Adhesion and friction of this segregated surface layer are higher than for the bulk cobalt base alloy composition. Auger spectroscopy analysis of the segregation of tungsten in the alloy indicates that it occurs between 850 and 1000 C.

  12. Co-Re-based alloys for high temperature applications: Design considerations and strengthening mechanisms

    NASA Astrophysics Data System (ADS)

    Mukherji, D.; Rösler, J.

    2010-07-01

    Cobalt-Rhenium base alloys are being developed for applications at temperatures beyond Ni-base superalloys. The high melting refractory element Re readily dissolves in Co and thereby changes the character of a Co-based alloy to a high melting point material. So far Co-Re system has not been investigated from the point of view of strengthening and oxidation and therefore different possibilities of strengthening mechanisms have been explored for our alloy development. Cr, a common element for oxidation resistance in many systems, is added along with Si in Co-Re alloys to improve oxidation behaviour at high temperatures.

  13. In vitro biocompatibility of novel Au-Pt-based metal-ceramic alloys.

    PubMed

    Johnson, Anthony; Shiraishi, Takanobu; Hurrell-Gillingham, Kathryn

    2011-09-01

    The aim of this research was to evaluate the effect of individual metallic elements within experimental Au-Pt-based metal-ceramic alloys on in vitro biocompatibility. A binary Au-10 at.% Pt alloy (AP10) was designed as a parent alloy. Six ternary AP10-X (X = In/Fe/Sn/Zn) alloys and four quaternary (AP10-In2)-Y (Y = Fe/Sn/Zn) with different compositions were cast into square plates with size 10X10X0.5 mm(3) and subjected to porcelain-firing thermal cycling. A commercial alloy was used as a control. In vitro biocompatibility was investigated using L929 murine aneuploid fibrosarcoma cell line. The test samples and cells were incubated at 37°C in a 5% CO(2) atmosphere for 72 h. Alamar™ Blue Assay was carried out to determine the respiratory viability of cultures maintained in the presence of the different materials. The cell only control showed significantly higher levels of cell viability than all six of the ternary alloys and two of the four quaternary alloys, (AP10-In2)-Zn2.1 and (AP10-In2)-Sn1.0 (P < 0.05). The quaternary alloys showed slightly higher levels of cell viability than the ternary alloys, with the exception of AP10-Sn0.9. No statistical differences were seen between the ternary and quaternary alloy groups. Acceptable cell viability was observed on the surfaces of all the alloys.

  14. Fabrication of a Mo based high temperature TZM alloy by non-consumable arc melting technique

    SciTech Connect

    Chakraborty, S.P.; Krishnamurthy, N.

    2014-07-01

    High temperature structural materials are in great demand for power, chemical and nuclear industries which can perform beyond 1000 °C as super alloys usually fail. In this regard, Mo based TZM alloy is capable of retaining strength up to 1500 °C with excellent corrosion compatibility against molten alkali metals. Hence, currently this alloy is considered an important candidate material for high temperature compact nuclear and fusion reactors. Due to reactive nature of Mo and having high melting point, manufacturing this alloy by conventional process is unsuitable. Powder metallurgy technique has limited success due to restriction in quantity and purity. This paper deals with fabrication of TZM alloy by nonconsumable tungsten arc melting technique. Initially a ternary master alloy of Mo-Ti-Zr was prepared which subsequently by dilution method, was converted into TZM alloy gradually by external addition of Mo and C in various proportions. A number of melting trials were conducted to optimize the process parameters like current, voltage and time to achieve desired alloy composition. The alloy was characterized with respect to composition, elemental distribution profile, microstructure, hardness profile and phase analysis. Well consolidated alloy button was obtained having desired composition, negligible material loss and having microstructure as comparable to standard TZM alloy. (author)

  15. Stable platinum nanoparticles on specific MgAl2O4 spinel facets at high temperatures in oxidizing atmospheres

    SciTech Connect

    Li, Wei-Zhen; Kovarik, Libor; Mei, Donghai; Liu, Jun; Wang, Yong; Peden, Charles H. F.

    2013-09-25

    The development of thermally stable, nanometer-sized precious metal-based catalysts remains a daunting challenge. Such materials, especially those based on the use of costly platinum metal, are essential and, to date, non-replaceable for a large number of industrially important catalytic processes. Here we report a well-defined cuboctahedral MgAl2O4 spinel support material that is capable of stabilizing platinum particles in the range of 1–3 nm on its relatively abundant {111} facets during extremely severe aging at 800 °C in air for 1 week. The aged catalysts retain platinum dispersions of 15.9% with catalytic activities for methanol oxidation being ~80% of that of fresh ones, whereas a conventional Pt/γ-Al2O3 catalyst is severely sintered and nearly inactive. Finally, we reveal the origin of the markedly superior ability of spinel {111} facets, resulting from strong interactions between spinel surface oxygens and epitaxial platinum {111} facets, inspiring the rational design of anti-sintering supported platinum group catalysts.

  16. Differences in photoluminescence properties and thermal degradation between nanoparticle and bulk particle BaMgAl10O17:Eu2+ phosphors under UV?VUV irradiation.

    PubMed

    Liu, Bitao; Xin, Shuangyu; Li, Fenghua; Zhang, Jiachi; Wang, Yuhua

    2014-05-01

    BaMgAl10O17:Eu2+ (BAM) phosphors used for plasma display panels and three-band fluorescence lamps are exposed to an oxidizing environment at about 500 degrees C, which is currently unavoidable in actual applications. We investigated the mechanism of the luminance degradation of BAM caused by annealing at 500 degrees C based on the difference in luminance degradation of bulk particle and nanoparticle samples under various excitation source irradiations. When the samples were excited by the different light sources, more than 30% degradation of luminance occurred under 147 nm while less than 10% degradation occurred under 254 nm both for nanoparticle and bulk particle samples. In addition, the luminescence degradation of nanophosphors shows a different tendency compared to the bulk phosphors. With a model based on the particle size and excitation light penetration depth, we demonstrate that the degradation is still mainly ascribed to the oxidized of divalent Eu. The differences in luminescence properties between nanophosphors and bulk phosphors are also illustrated by this model. As a result, the potential industrial applications of nanophosphors are evaluated.

  17. HIP clad nickel base Alloy 625 for deep sour wells

    SciTech Connect

    Uhl, W.K.; Pendley, M.R.

    1984-05-01

    The hot isostatic pressing (HIP) process was used to clad nickel base Alloy 625 to AISI 4130 low alloy steel. The performance of the HIP clad material in the corrosive environment characteristic of deep, sour oil and gas wells was evaluated in laboratory tests. Included in the test program were NACE TM-01-77 sulfide stress cracking tests, chloride stress corrosion cracking tests in boiling MgCl /SUB 2'/ , and pitting and crevice corrosion tests. The HIP clad 625 performed excellently, displaying essentially the same corrosion resistance as wrought 625. Specifically the HIP clad 625 resisted sulfide stress cracking at applied stresses as high as 120% of yield strength and resisted chloride stress corrosion cracking at stresses exceeding 100% of yield. The HIP clad 625 also displayed immunity to pitting and crevice corrosion, with corrosion rates of <0.025 mm/y (1 mil/y). The 4130 base metal, however, was attacked severly in all tests. SEM/EDX analysis of the 625/4130 interface demonstrated that dilution of the cladding by the base metal was essentially eliminated.

  18. Effect of Alloy 625 Buffer Layer on Hardfacing of Modified 9Cr-1Mo Steel Using Nickel Base Hardfacing Alloy

    NASA Astrophysics Data System (ADS)

    Chakraborty, Gopa; Das, C. R.; Albert, S. K.; Bhaduri, A. K.; Murugesan, S.; Dasgupta, Arup

    2016-04-01

    Dashpot piston, made up of modified 9Cr-1Mo steel, is a part of diverse safety rod used for safe shutdown of a nuclear reactor. This component was hardfaced using nickel base AWS ER NiCr-B alloy and extensive cracking was experienced during direct deposition of this alloy on dashpot piston. Cracking reduced considerably and the component was successfully hardfaced by application of Inconel 625 as buffer layer prior to hardface deposition. Hence, a separate study was undertaken to investigate the role of buffer layer in reducing the cracking and on the microstructure of the hardfaced deposit. Results indicate that in the direct deposition of hardfacing alloy on modified 9Cr-1Mo steel, both heat-affected zone (HAZ) formed and the deposit layer are hard making the thickness of the hard layer formed equal to combined thickness of both HAZ and deposit. This hard layer is unable to absorb thermal stresses resulting in the cracking of the deposit. By providing a buffer layer of Alloy 625 followed by a post-weld heat treatment, HAZ formed in the modified 9Cr-1Mo steel is effectively tempered, and HAZ formed during the subsequent deposition of the hardfacing alloy over the Alloy 625 buffer layer is almost completely confined to Alloy 625, which does not harden. This reduces the cracking susceptibility of the deposit. Further, unlike in the case of direct deposition on modified 9Cr-1Mo steel, dilution of the deposit by Ni-base buffer layer does not alter the hardness of the deposit and desired hardness on the deposit surface could be achieved even with lower thickness of the deposit. This gives an option for reducing the recommended thickness of the deposit, which can also reduce the risk of cracking.

  19. MODELING OF NI-CR-MO BASED ALLOYS: PART II - KINETICS

    SciTech Connect

    Turchi, P A; Kaufman, L; Liu, Z

    2006-07-07

    The CALPHAD approach is applied to kinetic studies of phase transformations and aging of prototypes of Ni-Cr-Mo-based alloys selected for waste disposal canisters in the Yucca Mountain Project (YMP). Based on a previous study on alloy stability for several candidate alloys, the thermodynamic driving forces together with a newly developed mobility database have been used to analyze diffusion-controlled transformations in these Ni-based alloys. Results on precipitation of the Ni{sub 2}Cr-ordered phase in Ni-Cr and Ni-Cr-Mo alloys, and of the complex P- and {delta}-phases in a surrogate of Alloy 22 are presented, and the output from the modeling are compared with experimental data on aging.

  20. Method for improve x-ray diffraction determinations of residual stress in nickel-base alloys

    DOEpatents

    Berman, Robert M.; Cohen, Isadore

    1990-01-01

    A process for improving the technique of measuring residual stress by x-ray diffraction in pieces of nickel-base alloys which comprises covering part of a predetermined area of the surface of a nickel-base alloy with a dispersion, exposing the covered and uncovered portions of the surface of the alloy to x-rays by way of an x-ray diffractometry apparatus, making x-ray diffraction determinations of the exposed surface, and measuring the residual stress in the alloy based on these determinations. The dispersion is opaque to x-rays and serves a dual purpose since it masks off unsatisfactory signals such that only a small portion of the surface is measured, and it supplies an internal standard by providing diffractogram peaks comparable to the peaks of the nickel alloy so that the alloy peaks can be very accurately located regardless of any sources of error external to the sample.

  1. Method for improving x-ray diffraction determinations of residual stress in nickel-base alloys

    DOEpatents

    Berman, R.M.; Cohen, I.

    1988-04-26

    A process for improving the technique of measuring residual stress by x-ray diffraction in pieces of nickel-base alloys is discussed. Part of a predetermined area of the surface of a nickel-base alloy is covered with a dispersion. This exposes the covered and uncovered portions of the surface of the alloy to x-rays by way of an x-ray diffractometry apparatus, making x-ray diffraction determinations of the exposed surface, and measuring the residual stress in the alloy based on these determinations. The dispersion is opaque to x-rays and serves a dual purpose, since it masks off unsatisfactory signals such that only a small portion of the surface is measured, and it supplies an internal standard by providing diffractogram peaks comparable to the peaks of the nickel alloy so that the alloy peaks can be very accurately located regardless of any sources of error external to the sample. 2 figs.

  2. An in vitro comparison of tensile bond strengths of noble and base metal alloys to enamel.

    PubMed

    Parsa, Roya Zand; Goldstein, Gary R; Barrack, Gerald M; LeGeros, Racquel Z

    2003-08-01

    Many different surface treatments have been used to increase the bond strength of noble and base metal alloys to enamel, but only a few have been studied. The purpose of this in vitro study was to compare the tensile bond strength of a tin-plated noble alloy, an Alloy Primer-treated noble alloy, and an airborne particle-abraded base metal alloy, all bonded to enamel with a phosphate-methacrylate resin luting agent. Seventy noncarious molar teeth were extracted, cleaned, and embedded in autopolymerizing acrylic resin with the buccal surface of the teeth exposed. Seventy wax patterns (4-mm diameter x 2-mm thickness) were waxed, invested, and cast-50 with a noble alloy (Argedent 52) and 20 with a base metal alloy (Argeloy N.P.). Twenty of the noble alloy specimens were tin-plated (TP), 20 noble alloy specimens were treated with Alloy Primer (AP), and 20 base metal alloy specimens were airborne particle abraded (AA). All specimens were luted with a phosphate-methacrylate resin luting agent (Panavia F) and stored in 100% humidity at 37 degrees C, half for 24 hours and half for 7 days. Ten noble alloy specimens were tin-plated and stored in water for 48 hours (aged) before cementation and then stored in water for 24 hours after cementation. These specimens were used to test whether there is an advantage to aging the tin-plated surface in water before cementation. All specimens were thermocycled (5 degrees to 55 degrees C) for 500 cycles and then tested for tensile bond strength (TBS), measured in MPa, with a universal testing machine at a crosshead speed of 0.5mm/min. Various castings (n=6 per test group) were randomly selected from each group and inspected under a scanning electronic microscope to determine mode of failure. The mean values and standard deviations of all specimens were calculated for each group. A 2-way analysis of variance (ANOVA) was performed, and multiple pairwise comparisons were then completed with post hoc Tukey test (alpha=.05). The TBS of the

  3. Method for producing La/Ce/MM/Y base alloys, resulting alloys and battery electrodes

    DOEpatents

    Gschneidner, Jr., Karl A.; Schmidt, Frederick A.

    2016-12-20

    A carbothermic reduction method is provided for reducing a La-, Ce-, MM-, and/or Y-containing oxide in the presence of carbon and a source of a reactant element comprising Si, Ge, Sn, Pb, As, Sb, Bi, and/or P to form an intermediate alloy material including a majority of La, Ce, MM, and/or Y and a minor amount of the reactant element. The intermediate material is useful as a master alloy for in making negative electrode materials for a metal hydride battery, as hydrogen storage alloys, as master alloy additive for addition to a melt of commercial Mg and Al alloys, steels, cast irons, and superalloys; or in reducing Sm.sub.2O.sub.3 to Sm metal for use in Sm--Co permanent magnets.

  4. Effect of different alloyed layers on the high temperature oxidation behavior of newly developed Ti 2AlNb-based alloys

    NASA Astrophysics Data System (ADS)

    Wu, Hongyan; Zhang, Pingze; Zhao, Haofeng; Wang, Ling; Xie, Aigen

    2011-01-01

    The application of titanium aluminide orthorhombic alloys (O-phase alloys) as potential materials in aircraft and jet engines was limited by their poor oxidation resistance at high temperature. The Ti 2AlNb-based alloys were chromised (Cr), chromium-tungstened (Cr-W) and nickel-chromised (Ni-Cr) by the double glow plasma surface alloying process to improve their high temperature oxidation resistance. The discontinuous oxidative behavior of Cr, Cr-W and Ni-Cr alloyed layers on Ti 2AlNb-based alloy at 1093 K was explored in this study. After exposing at 1093 K, the TiO 2 layer was formed on the bare alloy and accompanied by the occurrence of crack, which promoted oxidation rate. The oxidation behavior of Ti 2AlNb-based alloys was improved by surface alloying due to the formation of protective Al 2O 3 scale or continuous and dense NiCr 2O 4 film. The Ni-Cr alloyed layer presented the best high-temperature oxidation resistance among three alloyed layers.

  5. Competitive adsorption characteristics of fluoride and phosphate on calcined Mg-Al-CO3 layered double hydroxides.

    PubMed

    Cai, Peng; Zheng, Hong; Wang, Chong; Ma, Hongwen; Hu, Jianchao; Pu, Yubing; Liang, Peng

    2012-04-30

    With synthetic wastewater, competitive adsorption characteristics of fluoride and phosphate on calcined Mg-Al-CO(3) layered double hydroxides (CLDH) were investigated. A series of batch experiments were performed to study the influence of various experimental parameters, such as pH, contact time, and order of addition of the anions on the competitive adsorption of fluoride and phosphate on CLDH. It was found that the optimal pH is around 6 and it took 24 h to attain equilibrium when fluoride and phosphate were simultaneous added. The order of addition of anions influenced the adsorption of fluoride and phosphate on CLDH. The kinetic data were analyzed using the pseudo first-order and pseudo second-order models and they were found to fit very well the pseudo second-order kinetic model. Data of equilibrium experiments were fitted well to Langmuir isotherm and the competitive monolayer adsorption capacities of fluoride and phosphate were found to be obviously lower than those of single anion at 25 °C. The results of X-ray diffraction, Scanning Electron Microscopy with energy-dispersive X-ray analyses, and ATR-FTIR demonstrate that the adsorption mechanism involves the rehydration of mixed metal oxides and concomitant intercalation of fluoride and phosphate ions into the interlayer to reconstruct the initial LDHs structure.

  6. 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.

  7. Insights into the flexibility of ZrMxOy (M = Na, Mg, Al) nanofibrous membranes as promising infrared stealth materials.

    PubMed

    Mao, Xue; Bai, Ying; Yu, Jianyong; Ding, Bin

    2016-04-21

    A surprising brittle to flexible transition in ZrMxOy (M = Na, Mg, Al) nanofibrous membranes was found by varying the undersized dopant species and content. The fiber morphology, crystalline structure, and pore structure of the ZrMxOy nanofibrous membranes can be significantly modulated by varying the dopant valence from +1 to 3 and the dopant content from 1 to 20 mol%, respectively. Meanwhile, a classical Hall-Petch effect was revealed for the ZrMxOy nanofibrous membranes systems, which corresponded to a nanocrystalline size of 22.8 nm and an enhanced flexibility of 23 mN. Moreover, the substitutional solid solution and interstitial solid solution dissolution processes of Na, Mg, and Al into ZrO2 were analyzed using vacancy compensation and dopant interstitial compensation mechanisms, respectively. Most importantly, the flexible Al doped zirconia nanofibrous membranes exhibit a low infrared emissivity of 0.589 and 0.703 in the 3-5 μm and 8-14 μm wavebands, respectively, which suggests them to be a promising candidate for infrared stealth materials in the confrontation strategy field for personnel, aircraft, missiles, satellites, etc.

  8. Agronomic Effectiveness of Granulated and Powdered P-Exchanged Mg-Al LDH Relative to Struvite and MAP.

    PubMed

    Everaert, Maarten; Degryse, Fien; McLaughlin, Mike J; De Vos, Dirk; Smolders, Erik

    2017-08-16

    Layered double hydroxides (LDHs) used to recover P from wastewater have recently been proposed as new slow-release fertilizers. Here, the use of P-exchanged Mg-Al LDHs as powdered or granulated fertilizer is explored and compared with monoammonium phosphate (MAP), a fully water-soluble fertilizer, and with struvite, a recycled phosphate fertilizer with lower solubility. First, these three fertilizers were compared in a 100-day incubation experiment using P diffusion visualization and chemical analysis to assess P release from either granules or powdered fertilizer in three different soils. By the end of the incubation, 74-90% of P remained within the LDH granule, confirming a slow release. Second, a pot experiment was performed with wheat (Triticum aestivum) in an acid and a calcareous soil. The granular treatment resulted in a considerably higher P uptake for MAP compared to LDH and struvite. For the powder treatments, the P uptake was less than for granular MAP and was largely unaffected by the chemical form. The LDHs and struvite showed a lower agronomic effectiveness than granular MAP, but the benefits of their use in P recycling, potential residual value, and environmental benefits may render these slow-release fertilizers attractive.

  9. One-step production of biodiesel from oils with high acid value by activated Mg-Al hydrotalcite nanoparticles.

    PubMed

    Wang, Yi-Tong; Fang, Zhen; Zhang, Fan; Xue, Bao-Jin

    2015-10-01

    Activated Mg-Al hydrotalcite (HT-Ca) nanoparticles (<45 nm) were synthesized by co-precipitation and hydrothermal activation with aqueous Ca(OH)2 solution. They were characterized by various techniques including X-ray diffraction, inductively coupled plasma atomic-emission spectrometer, Brunauer-Emmett-Teller method, scanning electronic microscope-X-ray energy dispersive analysis and temperature programmed desorption method. HT-Ca presented both acidic and basic due to the formation of Mg4Al2(OH)14 · 3H2O, Mg2Al(OH)7 and AlO(OH) nanocrystals to esterify and transesterify oils with high acid value (AV). Under conditions of 5 wt% HT-Ca, 160 °C, 30/1 methanol/oil molar ratio and 4h, 93.4% Jatropha biodiesel yield was obtained at AV of 6.3 mg KOH/g with 4 cycles (biodiesel yield>86%). It was further found that it can resist free fatty acids, and biodiesel yield reached 92.9% from soybean oil with high AV of 12.1. HT-Ca catalyst showed a potential practical application for direct production of biodiesel from oils with high AV without pretreatment.

  10. Fabrication of Nanocomposites of SnO2 and MgAl2O4 for Gas Sensing Applications

    NASA Astrophysics Data System (ADS)

    Nithyavathy, N.; Arunmetha, S.; Vinoth, M.; Sriram, G.; Rajendran, V.

    2016-04-01

    Simple solid-state and sol-gel routes have been used to synthesize nanocomposites of tin oxide and magnesium aluminate at calcination temperature of 900 K for gas sensing applications. The effects of the surface structure of magnesium aluminate on the gas response for different concentrations of tin oxide addition were investigated for potential use in gas sensors. (SnO2) x doped in small amounts x into magnesium aluminate resulted in three nanocomposite samples MAS0.25, MAS0.50, and MAS0.75 for x = 0.25, 0.50, and 0.75, respectively, plus MgAl2O4 (MA) for x = 0. The response to different pressures of gases such as oxygen (O2), carbon monoxide (CO), and ethanol (C2H5OH) was quantitatively analyzed for all samples at different operating temperatures. The temperature was varied linearly by increasing the supply to a heating pad mounted below the sensor sample, regardless of the gas pressure inside the chamber. All the sample materials showed good response at different gas pressures (1 bar to 2 bar) and operating temperatures (300 K to 600 K). It was noted that the composite samples showed enhanced and fast response to gases, at both lower and higher operating temperatures, with detection of even the smallest change in gas pressure.

  11. Lattice strain and lattice expansion of nanoparticles of MgAl2O4 as a function of particle size.

    PubMed

    George, K C; Kurien, Siby; Mathew, Jose

    2007-06-01

    Reduction in the physical dimension of a crystalline solid lead to regular changes in the lattice constants. The lattice expansion or contraction in nanoparticles depend on a number of factors like nature of atoms in the interior, surface atoms, surface surroundings, dangling bonds, and oxygen concentration on the surface. XRD patterns of nanoparticles of MgAl2O4 having average particle size 7 nm, 9 nm, and 19 nm show that lattice parameters undergo contraction or repulsion along different planes. The lattice contraction along with lattice expansion is possible since the morphology of the particle is not spherical which is evident from the SEM micrographs. Lattice expansion is observed mainly in nanocrystals having covalent or ionic bonds. The existence of ionic bonds is evident from the IR spectrum. Along planes where there is no deficiency of oxygen, contraction is observed while where there is deficiency of oxygen lattice expansion is observed. As the particle size increases due to heating most of the planes show lattice contraction and on further heating due to the excess oxygen accumulation in interstitial positions lattice expansion is observed along most of the planes. The reason for the observation of lattice strain or lattice expansion may be due to the electrostatic attraction or repulsion between ions along different planes.

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

    PubMed

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

    2013-11-15

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

  13. 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.

  14. Surface passivation of MgAl2O4 spinel powder by chemisorbing H3PO4 for easy aqueous processing.

    PubMed

    Olhero, Susana M; Ganesh, Ibram; Torres, Paula M C; Ferreira, José M F

    2008-09-02

    A stoichiometric MgAl 2O 4 spinel (MAS) powder was synthesized by heat treating at 1400 degrees C for 2 h a compacted mixture of alpha-Al 2O 3 and calcined caustic MgO, followed by crushing and milling. The surface of this powder was then passivated against hydrolysis with H 3PO 4 and Al(H 2PO 4) 3 in an ethanol solution. The as-passivated powder could then be dispersed in water using tetramethylammonium hydroxide (TMAH) and an ammonium salt of poly(acrylic acid) (Duramax D-3005) as dispersing agents and gelcast to form green consolidates with relatively high strength (>15 MPa). The good dispersing behavior of the passivated powder in water was confirmed by the low viscosity of its suspension containing 41-45 vol % solids, demonstrating the viability of replacing organic solvents by water in colloidal processing of MAS-based ceramics. The Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and energy dispersive X-ray (EDAX) studies revealed that only negligible amounts of phosphate ions at the surface are required to effectively protect the powder from reacting with water.

  15. A single source precursor for low temperature processing of nanocrystalline MgAl2O4 spinel: synthesis and characterization of [MgAl2(μ3-O)(μ2-O(i)Pr)4(O(i)Pr)2]4.

    PubMed

    Mohammadnezhad, Gholamhossein; Amini, Mostafa M; Khavasi, Hamid Reza

    2010-12-07

    A novel polynuclear single-source precursor was prepared and characterized by single-crystal X-ray diffraction and multinuclear NMR spectroscopy. Nano-crystalline MgAl(2)O(4) spinel was synthesized via sol-gel processing of [MgAl(2)(μ(3)-O)(μ(2)-O(i)Pr)(4)(O(i)Pr)(2)](4). XRD, TGA-DSC and HRTEM confirmed the formation of a spinel phase at 475 °C, a temperature lower than any known processing temperature for MgAl(2)O(4).

  16. Near-Threshold Fatigue Crack Growth Behavior of Fine-Grain Nickel-Based Alloys

    NASA Technical Reports Server (NTRS)

    Newman, John A.; Piascik, Robert S.

    2003-01-01

    Constant-Kmax fatigue crack growth tests were performed on two finegrain nickel-base alloys Inconel 718 (DA) and Ren 95 to determine if these alloys exhibit near-threshold time-dependent crack growth behavior observed for fine-grain aluminum alloys in room-temperature laboratory air. Test results showed that increases in K(sub max) values resulted in increased crack growth rates, but no evidence of time-dependent crack growth was observed for either nickel-base alloy at room temperature.

  17. Co-based alloys design based on first-principles calculations: Influence of transition metal and rare-earth alloying element on stacking fault energy

    NASA Astrophysics Data System (ADS)

    Achmad, Tria Laksana; Fu, Wenxiang; Chen, Hao; Zhang, Chi; Yang, Zhi-Gang

    2017-01-01

    The main idea of alloy design is to reduce costs and time required by the traditional (trial and error) method, then finding a new way to develop the efficiency of the alloy design is necessary. In this study, we proposed a new approach to the design of Co-based alloys. It is based on the concept that lowering the ratio of stable and unstable stacking fault energy (SFE) could bring a significant increase in the tendency of partial dislocation accumulation and FCC to HCP phase transformation then enhance mechanical properties. Through the advance development of the computing techniques, first-principles density-functional-theory (DFT) calculations are capable of providing highly accurate structural modeling at the atomic scale without any experimental data. The first-principles calculated results show that the addition of some transition metal (Cr, Mo, W, Re, Os, Ir) and rare-earth (Sc, Y, La, Sm) alloying elements would decrease both stable and unstable SFE of pure Co. The dominant deformation mechanism of binary Co-4.5 at.% X (X = alloying element) is extended partial dislocation. Our study reveals Re, W, Mo and La as the most promising alloying additions for the Co-based alloys design with superior performances. Furthermore, the underlying mechanisms for the SFE reduction can be explained regarding the electronic structure.

  18. Effect of composition on antiphase boundary energy in Ni3Al based alloys: Ab initio calculations

    NASA Astrophysics Data System (ADS)

    Gorbatov, O. I.; Lomaev, I. L.; Gornostyrev, Yu. N.; Ruban, A. V.; Furrer, D.; Venkatesh, V.; Novikov, D. L.; Burlatsky, S. F.

    2016-06-01

    The effect of composition on the antiphase boundary (APB) energy of Ni-based L 12-ordered alloys is investigated by ab initio calculations employing the coherent potential approximation. The calculated APB energies for the {111} and {001} planes reproduce experimental values of the APB energy. The APB energies for the nonstoichiometric γ' phase increase with Al concentration and are in line with the experiment. The magnitude of the alloying effect on the APB energy correlates with the variation of the ordering energy of the alloy according to the alloying element's position in the 3 d row. The elements from the left side of the 3 d row increase the APB energy of the Ni-based L 12-ordered alloys, while the elements from the right side slightly affect it except Ni. The way to predict the effect of an addition on the {111} APB energy in a multicomponent alloy is discussed.

  19. Progress in the Modeling of NiAl-Based Alloys Using the BFS Method

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Noebe, Ronald D.; Ferrante, John; Garg, Anita

    1997-01-01

    The BFS method has been applied to the study of NiAl-based materials to assess the effect of alloying additions on structure. Ternary, quaternary and even pent-alloys based on Ni-rich NiAl with additions of Ti, Cr and Cu were studied. Two approaches were used, Monte Carlo simulations to determine ground state structures and analytical calculations of high symmetry configurations which give physical insight into preferred bonding. Site occupancy energetics for ternary and the more complicated case of quaternary additions were determined, and solubility limits and precipitate formation with corresponding information concerning structure and lattice parameter were also 'observed' computationally. The method was also applied to determine the composition of alloy surfaces and interfaces. Overall, the results demonstrate that the BFS method for alloys is a powerful tool for alloy design and with its simplicity and obvious advantages can be used to complement any experimental alloy design program.

  20. In vitro corrosion of dental Ag-based alloys in polyvinylpyrrolidone iodine solution.

    PubMed

    Ochi, Morio; Endo, Kazuhiko; Ohno, Hiroki; Takasusuki, Norio; Matsubara, Hideki; Maida, Takeo

    2005-09-01

    The corrosion and tarnish behaviors of three Ag-based alloys (Ag-Pd-Cu-Au alloy, Ag-In alloy, and Ag-Sn-Zn alloy) in polyvinylpyrrolidone iodine (povidone-iodine) solution were examined. The degree of tarnish was evaluated by visible-ray spectrocolorimetry. Corrosion potential measurements and analyses of corrosion products by X-ray diffractometry were carried out to elucidate the corrosion mechanism. The corrosion rate of the three Ag-based alloys in povidone-iodine solution at its practical concentration used as a gargle solution was so fast that the alloys tarnished within 10 seconds of immersion with the formation of AgI. Thermodynamic consideration and the results of surface analysis by X-ray diffractometry revealed that the main anodic and cathodic reactions were Ag + I(-)-->AgI + e- and I2 + 2e(-)-->2I- respectively.

  1. Combinatorial density functional theory-based screening of surface alloys for the oxygen reduction reaction.

    SciTech Connect

    Greeley, J.; Norskov, J.; Center for Nanoscale Materials; Technical Univ. of Denmark

    2009-03-26

    A density functional theory (DFT) -based, combinatorial search for improved oxygen reduction reaction (ORR) catalysts is presented. A descriptor-based approach to estimate the ORR activity of binary surface alloys, wherein alloying occurs only in the surface layer, is described, and rigorous, potential-dependent computational tests of the stability of these alloys in aqueous, acidic environments are presented. These activity and stability criteria are applied to a database of DFT calculations on nearly 750 binary transition metal surface alloys; of these, many are predicted to be active for the ORR but, with few exceptions, they are found to be thermodynamically unstable in the acidic environments typical of low-temperature fuel cells. The results suggest that, absent other thermodynamic or kinetic mechanisms to stabilize the alloys, surface alloys are unlikely to serve as useful ORR catalysts over extended periods of operation.

  2. Adhesion and friction of iron-base binary alloys in contact with silicon carbide in vacuum

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1980-01-01

    Single pass sliding friction experiments were conducted with various iron base binary alloys (alloying elements were Ti, Cr, Mn, Ni, Rh, and W) in contact with a single crystal silicon carbide /0001/ surface in vacuum. Results indicate that atomic size and concentration of alloying elements play an important role in controlling adhesion and friction properties of iron base binary alloys. The coefficient of friction generally increases with an increase in solute concentration. The coefficient of friction increases linearly as the solute to iron atomic radius ratio increases or decreases from unity. The chemical activity of the alloying elements was also an important parameter in controlling adhesion and friction of alloys, as these latter properties are highly dependent upon the d bond character of the elements.

  3. High Temperature Mechanical Behavior of MgAl2O4-YAG Eutectic Ceramic In Situ Composites by Float Zone Method

    NASA Astrophysics Data System (ADS)

    Abalı, Serkan

    2017-09-01

    The directionally solidified eutectic MgAl2O4-Y3Al5O12 crystal was prepared at a pressure of 0.4 MPa of ambient nitrogen gas by the high frequency induction heated floating zone furnace. In order to determine the high temperature characteristics, directionally solidified MgAl2O4-Y3Al5O12 eutectic phase has been analyzed with creep test, tensile strength, young modulus and fracture toughness at the various temperatures and the microstructural variations have been studied according to the analysis results. It has been seen that directionally solidified with zone melting MgAl2O4-YAG eutectic ceramic which has given the value of 168 MPa below 10-6/s strain rate at 1,700 °C temperature has revealed minimum stress.

  4. 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.

  5. Perpendicular magnetic anisotropy at lattice-matched Co2FeAl/MgAl2O4(001) epitaxial interfaces

    NASA Astrophysics Data System (ADS)

    Sukegawa, Hiroaki; Hadorn, Jason Paul; Wen, Zhenchao; Ohkubo, Tadakatsu; Mitani, Seiji; Hono, Kazuhiro

    2017-03-01

    We report perpendicular magnetic anisotropy (PMA) induced at Co2FeAl/MgAl2O4(001) epitaxial interfaces prepared by magnetron sputtering and post-oxidation of MgAl layers. A PMA energy density of more than 4 Merg/cm3 for 1-nm-thick Co2FeAl layers and an effective interface PMA energy density of 1.6 erg/cm2 were achieved by controlling the interfacial oxidation states through fine-tuning of oxidation processes and annealing temperature. Cross-sectional scanning transmission electron microscopy imaging revealed a lattice-matched Co2FeAl/MgAl2O4 interface, which may be responsible for the large PMA energy due to a reduction of the bulk anisotropy contribution.

  6. Study of Alloy Microstructure Based on TiNi After High-Temperature Treatment

    NASA Astrophysics Data System (ADS)

    Senkevich, K. S.; Gusev, D. E.

    2016-09-01

    Features of microstructure formation for alloy based on titanium nickelide after high-temperature treatment at 1050 - 1250°C are studied. Heat treatment conditions are stipulated diffusion welding and sintering regimes developed previously for alloys based on TiNi.

  7. Some properties of a stir-cast Ni-Cr based dental alloy.

    PubMed

    Boswell, P G; Stevens, L

    1980-06-01

    A Ni-Cr based crown and bridge alloy has been successfully stir-cast into small investment mould spaces using a modified induction melting and casting machine. Stir-casting produced substantial improvements to the mechanical properties of the cast alloy. A model for the development of the stir-cast microstructure is described and the clinical significance of the improvements in the alloy's properties is discussed.

  8. Thermodynamic Modeling and Experimental Study of Phase Transformations in Alloys Based on γ-TiAl

    NASA Astrophysics Data System (ADS)

    Kuznetsov, A. V.; Sokolovskii, V. S.; Salishchev, G. A.; Belov, N. A.; Nochovnaya, N. A.

    2016-09-01

    Thermo-Calc software is used to model the composition diagram for alloys based on γ-TiAl of the systems Ti - Al - Mo - (4 - 10) at.% Nb and Ti - Al - Nb - X ( X is Cr, Mo, V). The effect of alloying on critical points and sequence of phase transformations is established. Changes in phase composition in relation to alloy TNM-B1 temperature are analyzed using a polythermal section of the Ti - Al - Nb - Mo system.

  9. Fundamental Understanding of the Intrinsic Ductility in Nickel-Base L1 sub 2 Type Alloys

    DTIC Science & Technology

    1988-06-30

    tantalum and niobium modified ternary alloys as published in the literature (References 9 and 16), in both cases here the > orientation is observed to be...applied to a nickel-base Llz phase compound. Large single crystals of binary and tantalum -modified V. Ni3Al alloys with various stoichiometry were...ductility of the tantalum -modified ternary alloys shows a rather different 0. OISTRIBUTION/AVAILABILITY OF ABSTRACT 21 ABSTRACT SECURITY CLASSIFICATION

  10. Helium Accumulation Behavior in Iron Based Model Alloys

    SciTech Connect

    Sugano, R.; Morishita, K.; Kimura, A.

    2003-09-15

    Helium desorption from Fe-based model alloys irradiated by energetic helium ions was measured during post-irradiation annealing to investigate the energetics and kinetics of formation and annihilation of helium-related defects. Desorption temperatures were observed to be widely ranged from 450 to 1500 K, indicating that helium is bound to a wide variety of trapping sites such as vacancies and dislocations at various binding states. Such a feature is also observed in fusion ferritic steel. A comparison of helium desorption spectra obtained using Fe, Fe-Cr and Fe-Cr-Ni alloys showed that helium is more strongly trapped in bcc Fe than fcc Fe. It indicates that the long distance migration of helium takes place less frequently in bcc matrix, which may reduce the probability of helium clustering. Fusion ferric steel has a lot of trapping sites for helium such as dislocations, solute atoms, the interface of precipitates, impurities and lath boundaries, and so on, and in addition, it has bct matrix, indicating that most of helium atoms must be dispersed in the matrix and therefore it is difficult for them to cluster as a bubble. This may be a reason for higher helium resistance of the steel.

  11. Oxidation/vaporization of silicide coated columbium base alloys

    NASA Technical Reports Server (NTRS)

    Kohl, F. J.; Stearns, C. A.

    1971-01-01

    Mass spectrometric and target collection experiments were made at 1600 K to elucidate the mode of oxidative vaporization of two columbium alloys, fused-slurry-coated with a complex silicide former (Si-20Cr-Fe). At oxygen pressures up to 0.0005 torr the major vapor component detected by mass spectrometry for oxidized samples was gaseous silicon monoxide. Analysis of condensates collected at oxygen pressures of 0.1, 1.0 and 10 torr revealed that chromium-, silicon-, iron- and tungsten- containing species were the major products of vaporization. Equilibrium thermochemical diagrams were constructed for the metal-oxygen system corresponding to each constituent metal in both the coating and base alloy. The major vaporizing species are expected to be the gaseous oxides of chromium, silicon, iron and tungsten. Plots of vapor phase composition and maximum vaporization rate versus oxygen pressure were calculated for each coating constituent. The major contribution to weight loss by vaporization at oxygen pressures above 1 torr was shown to be the chromium-containing species.

  12. A Shape Memory Alloy Based Cryogenic Thermal Conduction Switch

    NASA Technical Reports Server (NTRS)

    Notardonato, W. U.; Krishnan, V. B.; Singh, J. D.; Woodruff, T. R.; Vaidyanathan, R.

    2005-01-01

    Shape memory alloys (SMAs) can produce large strains when deformed (e.g., up to 8%). Heating results in a phase transformation and associated recovery of all the accumulated strain. This strain recovery can occur against large forces, resulting in their use as actuators. Thus an SMA element can integrate both sensory and actuation functions, by inherently sensing a change in temperature and actuating by undergoing a shape change as a result of a temperature-induced phase transformation. Two aspects of our work on cryogenic SMAs are addressed here. First - a shape memory alloy based cryogenic thermal conduction switch for operation between dewars of liquid methane and liquid oxygen in a common bulkhead arrangement is discussed. Such a switch integrates the sensor element and the actuator element and can be used to create a variable thermal sink to other cryogenic tanks for liquefaction, densification, and zero boil-off systems for advanced spaceport applications. Second - fabrication via arc-melting and subsequent materials testing of SMAs with cryogenic transformation temperatures for use in the aforementioned switch is discussed.

  13. Effects of neutron irradiation on deformation behavior of nickel-base fastener alloys

    SciTech Connect

    Bajaj, R.; Mills, W.J.; Kammenzind, B.F.; Burke, M.G.

    1999-07-01

    This paper presents the effects of neutron irradiation on the fracture behavior and deformation microstructure of high-strength nickel-base alloy fastener materials, Alloy X-750 and Alloy 625. Alloy X-750 in the HTH condition, and Alloy 625 in the direct aged condition were irradiated to a fluence of 2.4x10{sup 20} n/cm{sup 2} at 264 C in the Advanced Test Reactor. Deformation structures at low strains were examined. It was previously shown that Alloy X-750 undergoes hardening, a significant degradation in ductility and an increase in intergranular fracture. In contrast, Alloy 625 had shown softening with a concomitant increase in ductility and transgranular failure after irradiation. The deformation microstructures of the two alloys were also different. Alloy X-750 deformed by a planar slip mechanism with fine microcracks forming at the intersections of slip bands with grain boundaries. Alloy 625 showed much more homogeneous deformation with fine, closely spaced slip bands and an absence of microcracks. The mechanism(s) of irradiation assisted stress corrosion cracking (IASCC) are discussed.

  14. Thermal analysis of a diffusion bonded Er3+,Yb3+:glass/Co2+: MgAl2O4 microchip lasers

    NASA Astrophysics Data System (ADS)

    Belghachem, Nabil; Mlynczak, Jaroslaw; Kopczynski, krzysztof; Mierczyk, Zygmunt; Gawron, Michal

    2016-10-01

    The analysis of thermal effects in a diffusion bonded Er3+,Yb3+:glass/Co2+:MgAl2O4 microchip laser is presented. The analysis is performed for both wavelengths at 940 nm and at 975 nm as well as for two different sides of pumping, glass side and saturable absorber side. The heat sink effect of Co2+:MgAl2O4, as well as the impact of the thermal expansion and induced stress on the diffusion bonding are emphasised. The best configurations for reducing the temperature peaks, the Von Mises stresses on the diffusion bonding, and the thermal lensing are determined.

  15. Stabilization of MgAl2O4 spinel surfaces via doping

    SciTech Connect

    Hasan, Md. M.; Dholabhai, Pratik P.; Castro, Ricardo H. R.; Uberuaga, Blas P.

    2016-02-06

    Here, the surface structure of complex oxides plays a vital role in processes such as sintering, thin film growth, and catalysis, as well as being a critical factor determining the stability of nanoparticles. We report atomistic calculations of the low-index stoichiometric magnesium aluminate spinel (MgAl2O4) surfaces, each with two different chemical terminations. High temperature annealing was used to explore the potential energy landscape and provide more stable surface structures. We find that the lowest energy surface is {100} while the highest energy surface is {111}. The surfaces were subsequently doped with three trivalent dopants (Y3+, Gd3+, La3+) and one tetravalent dopant (Zr4+) and both the surface segregation energies of the dopants and surface energies of the doped surface were determined. All of the dopants reduce the surface energy of spinel, though this reduction in energy depends on both the size and valence of the dopant. Dopants with larger ionic radius tend to segregate to the surface more strongly and reduce the surface energy to a greater extent. Furthermore, the ionic valence of the dopants seems to have a stronger influence on the segregation than does ionic size. For both undoped and doped spinel, the predicted crystal shape is dominated by {100} surfaces, but the relative fraction of the various surfaces changes with doping due to the unequal changes in energy, which has implications on equilibrium nanoparticle shapes and therefore on applications sensitive to surface properties.

  16. 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.

  17. Photoinduced radical processes on the spinel (MgAl2O4) surface involving methane, ammonia, and methane/ammonia.

    PubMed

    Emeline, A V; Abramkin, D A; Zonov, I S; Sheremetyeva, N V; Rudakova, A V; Ryabchuk, V K; Serpone, N

    2012-05-15

    The present study explored photoinduced radical processes caused by interaction of CH(4) and NH(3) with a photoexcited surface of a complex metal oxide: magnesium-aluminum spinel (MgAl(2)O(4); MAS). UV irradiation of MAS in vacuo yielded V-type color centers as evidenced by the 360 nm band in difference diffuse reflectance spectra. Interaction of these H-bearing molecules with photogenerated surface-active hole states (O(S)(-)•) yielded radical species which on recombination produced more complex molecules (including heteroatomic species) relative to the initial molecules. For the MAS/CH(4) system, photoinduced dissociative adsorption of CH(4) on surface-active hole centers produced •CH(3) radicals that recombined to yield CH(3)CH(3). For MAS/NH(3), a similar dissociative adsorption process led to formation of •NH(2) radicals with formation of NH(2)NH(2) as an intermediate product; continued UV irradiation ultimately yielded N(2). For the mixed MAS/CH(4)/NH(3) system, however, interaction of adsorbed NH(3) and CH(4) on the UV-activated surface of MAS yielded •NH(2) and •CH(3) radicals, respectively, which produced CH(3)-NH(2) followed by loss of the remaining hydrogens to form a surface-adsorbed cyanide, CN(S), species. Recombination of photochemically produced radicals released sufficient energy to re-excite the solid spinel, generating new surface-active sites and a flash luminescence (emission decay time at 520 nm, τ ~ 6 s for the MAS/NH(3) case) referred to as the PhICL effect.

  18. Adsorption Assisted Photocatalytic Removal of Methyl Orange by MgAl2O4-Sb2S3 Composite Material.

    PubMed

    Muneeb, Muhammad; Ismail, Bushra; Fazal, Tanzeela; Khan, Abdur Rehman; Afzia, Mehwish

    2016-01-01

    The current article is about the water treatment in which colored water contaminated by methyl orange has been used for adsorption assisted photocatalysis. Coupling of photocatalysis with the traditional water treatment processes has been in practice since last couple of years for the improvement of degradation efficiencies, for example, photocatalysis coupled with ultrafilteration, adsorption, flocculation, biological methods, photolysis, membrane distillation, etc. Among all these coupling approaches, adsorption assisted photocatalysis being a very simple and highly efficient approach is suffering from few drawbacks on the account of high cost, low stability and surface area of the adsorbent support. The present study is a contribution towards improvement in this coupling approach. A low cost, highly stable spinel magnesium aluminate (MgAl2O4) material synthesized at nanoscale is used for composite formation with antimony sulphide (Sb2S3) material having high absorption coefficient in the visible light of solar spectrum. A review of recent patents shows that the field of photoctalysis is dominated by the traditional TiO2 catalyst. The modification of TiO2 by either composite formation or by doping is the main focus. Coprecipitation method is used for the synthesis of spinel in which the desired precursors in the respective molar ratios were mixed and annealing of the resulting precipitates was carried out at 800oC for 8 h. Sb2S3 was synthesized by the hydrothermal method in which the required molar solution of precursors was mixed with urea solution and the whole mixture was maintained at 105oC for 6 hrs in a Teflon lined autoclave. The resulting suspension was then annealed at 37oC for 3 hours. The composite of Sb2S3 and MgAl2O4 has been synthesized by mixing both the materials in 1:1 and heat treated in an oven at a temperature of 200oC. Peaks in X-ray diffraction pattern correspond to both the Sb2S3 and spinel phase. All the peaks corresponding to the Sb2S3

  19. Thermodynamics-Based Computational Design of Al-Mg-Sc-Zr Alloys

    NASA Astrophysics Data System (ADS)

    Haidemenopoulos, G. N.; Katsamas, A. I.; Kamoutsi, H.

    2010-04-01

    Alloying additions of Sc and Zr raise the yield strength of Al-Mg alloys significantly. We have studied the effects of Sc and Zr on the grain refinement and recrystallization resistance of Al-Mg alloys with the aid of computational alloy thermodynamics. The grain refinement potential has been assessed by Scheil-Gulliver simulations of solidification paths, while the recrystallization resistance (Zener drag) has been assessed by calculation of the precipitation driving forces of the Al3Sc and Al3Zr intermetallics. Microstructural performance indices have been derived, used to rank several alloy composition variants, and finally select the variant with the best combination of grain refinement and recrystallization resistance. The method can be used, with certain limitations, for a thermodynamics-based design of Al-Mg and other alloy compositions.

  20. Dual Microstructure Heat Treatment of a Nickel-Base Disk Alloy

    NASA Technical Reports Server (NTRS)

    Gayda, John

    2001-01-01

    Existing Dual Microstructure Heat Treat (DMHT) technology was successfully applied to Alloy 10, a high strength, nickel-base disk alloy, to produce a disk with a fine grain bore and coarse grain rim. Specimens were extracted from the DMHT disk and tested in tension, creep, fatigue, and crack growth using conditions pertinent to disk applications. These data were then compared with data from "traditional" subsolvus and supersolvus heat treatments for Alloy 10. The results showed the DMHT disk to have a high strength, fatigue resistant bore comparable to that of subsolvus Alloy 10. Further, creep resistance of the DMHT rim was comparable to that of supersolvus Alloy 10. Crack growth resistance in the DMHT rim, while better than that for subsolvus, was inferior to that of supersolvus Alloy 10. The slow cool at the end of the DMHT conversion and/or the subsolvus resolution step are thought to be responsible for degrading rim DMHT crack growth resistance.

  1. Evaluation of Nb-base alloys for the divertor structure in fusion reactors

    SciTech Connect

    Purdy, I.M.

    1996-04-01

    Niobium-base alloys are candidate materials for the divertor structure in fusion reactors. For this application, an alloy should resist aqueous corrosion, hydrogen embrittlement, and radiation damage and should have high thermal conductivity and low thermal expansion. Results of corrosion and embrittlement screening tests of several binary and ternary Nb alloys in high-temperature water indicated the Mb-1Zr, Nb-5MO-1Zr, and Nb-5V-1Z4 (wt %) showed sufficient promise for further investigation. These alloys, together with pure Nb and Zircaloy-4 have been exposed to high purity water containing a low concentration of dissolved oxygen (<12 ppb) at 170, 230, and 300{degrees}C for up to {approx}3200 h. Weight-change data, microstructural observations, and qualitative mechanical-property evaluation reveal that Nb-5V-1Zr is the most promising alloy at higher temperatures. Below {approx}200{degrees}C, the alloys exhibit similiar corrosion behavior.

  2. Transformation of the θ-phase in Mg-Li-Al alloys: a density functional theory study.

    PubMed

    Zhang, Caili; Han, Peide; Zhang, Zhuxia; Dong, Minghui; Zhang, Lili; Gu, Xiangyang; Yang, Yanqing; Xu, Bingshe

    2012-03-01

    In Mg-Li-Al alloys, θ-phase MgAlLi(2) is a strengthening and metastable phase which is liable to be transformed to the equilibrium phase AlLi on overaging. While the structural details of the θ-phase MgAlLi(2) and the microscopic transformation are still unknown. In this paper, the structure of MgAlLi(2) unit cell was determined through X-ray powder diffraction simulation. Microscopic transformation process of θ-phase MgAlLi(2) was discussed in detail using first principles method.

  3. Elements loss analysis based on spectral diagnosis in laser-arc hybrid welding of aluminum alloy

    NASA Astrophysics Data System (ADS)

    Chen, Yong; Chen, Hui; Zhu, Minhao; Yang, Tao; Shen, Lin

    2017-07-01

    Aluminum alloy has been widely used in automobiles, high-speed trains, aerospace and many other fields. The loss of elements during welding process causes welding defects and affects the microstructure and properties of the joints. This paper discusses the correlation between welding process, spectral intensity and loss of elements in laser-arc hybrid welding of Al alloys. The results show that laser power and arc current have a significant impact on the spectral intensity and loss of elements. Compared with the base metal, the contents of alloying elements in the weld area are lower. The burning losses of alloy elements increase with the welding heat input.

  4. Thermodynamic properties of gadolinium in Ga-Sn and Ga-Zn eutectic based alloys

    NASA Astrophysics Data System (ADS)

    Maltsev, Dmitry S.; Volkovich, Vladimir A.; Yamshchikov, Leonid F.; Chukin, Andrey V.

    2016-09-01

    Thermodynamic properties of gadolinium in Ga-Sn and Ga-Zn eutectic based alloys were studied. Temperature dependences of gadolinium activity in the studied alloys were determined at 573-1073 K employing the EMF method. Solubility of gadolinium in the Ga-Sn and Ga-Zn alloys was measured at 462-1073 K using IMCs sedimentation method. Activity coefficients as well as partial and excess thermodynamic functions of gadolinium in the studied alloys were calculated on the basis of the obtained experimental data.

  5. Hydrogen embrittlement considerations in niobium-base alloys for application in the ITER divertor

    SciTech Connect

    Peterson, D.T. ); Hull, A.B.; Loomis, B.A. )

    1991-01-01

    The ITER divertor will be subjected to hydrogen from aqueous corrosion by the coolant and by transfer from the plasma. Global hydrogen concentrations are one factor in assessing hydrogen embrittlement but local concentrations affected by source fluxes and thermotransport in thermal gradients are more important considerations. Global hydrogen concentrations is some corrosion- tested alloys will be presented and interpreted. The degradation of mechanical properties of Nb-base alloys due to hydrogen is a complex function of temperature, hydrogen concentration, stresses and alloy composition. The known tendencies for embrittlement and hydride formation in Nb alloys are reviewed.

  6. Hydrogen embrittlement considerations in niobium-base alloys for application in the ITER divertor

    SciTech Connect

    Peterson, D.T.; Hull, A.B.; Loomis, B.A.

    1991-12-31

    The ITER divertor will be subjected to hydrogen from aqueous corrosion by the coolant and by transfer from the plasma. Global hydrogen concentrations are one factor in assessing hydrogen embrittlement but local concentrations affected by source fluxes and thermotransport in thermal gradients are more important considerations. Global hydrogen concentrations is some corrosion- tested alloys will be presented and interpreted. The degradation of mechanical properties of Nb-base alloys due to hydrogen is a complex function of temperature, hydrogen concentration, stresses and alloy composition. The known tendencies for embrittlement and hydride formation in Nb alloys are reviewed.

  7. Insight into the phase evolution of a NiMgAl catalyst from the reduction stage to the post-reaction stage during the dry reforming of methane [Insight into the phase evolution of NiMgAl catalyst from reduction to post-reaction for dry reforming of methane

    DOE PAGES

    Bao, Zhenghong; Zhan, Yiqiu; Street, Jason; ...

    2017-05-04

    Herein, phase evolution of a NiMgAl oxide catalyst at the reduction stage was qualitatively analysed and quantitatively determined by employing the continuous changes in its XRD intensity and TPR information. In conclusion, the stable crystallite size of both the active metal and spinel support was responsible for the long stability of the NiMgAl catalyst without carbon deposition during the DRM reaction.

  8. Steam Oxidation Behavior of Advanced Steels and Ni-Based Alloys at 800 °C

    NASA Astrophysics Data System (ADS)

    Dudziak, T.; Boroń, L.; Deodeshmukh, V.; Sobczak, J.; Sobczak, N.; Witkowska, M.; Ratuszek, W.; Chruściel, K.

    2017-02-01

    This publication studies the steam oxidation behavior of advanced steels (309S, 310S and HR3C) and Ni-based alloys (Haynes® 230®, alloy 263, alloy 617 and Haynes® 282®) exposed at 800 °C for 2000 h under 1 bar pressure, in a pure water steam system. The results revealed that all exposed materials showed relatively low weight gain, with no spallation of the oxide scale within the 2000 h of exposure. XRD analysis showed that Ni-based alloys developed an oxide scale consisting of four main phases: Cr2O3 (alloy 617, Haynes® 282®, alloy 263 and Haynes® 230®), MnCr2O4 (alloy 617, Haynes® 282® and Haynes® 230®), NiCr2O4 (alloy 617) and TiO2 (alloy 263, Haynes® 282®). In contrast, advanced steels showed the development of Cr2O3, MnCr2O4, Mn7SiO12, FeMn(SiO4) and SiO2 phases. The steel with the highest Cr content showed the formation of Fe3O4 and the thickest oxide scale.

  9. Nanocrystalline Al-based alloys - lightweight materials with attractive mechanical properties

    NASA Astrophysics Data System (ADS)

    Latuch, J.; Cieslak, G.; Dimitrov, H.; Krasnowski, M.; Kulik, T.

    2009-01-01

    In this study, several ways of bulk nanocrystalline Al-based alloys' production by high-pressure compaction of powders were explored. The effect of chemical composition and compaction parameters on the structure, quality and mechanical properties of the bulk samples was studied. Bulk nanocrystalline Al-Mm-Ni-(Fe,Co) alloys were prepared by ball-milling of amorphous ribbons followed by consolidation. The maximum microhardness (540 HV0.1) was achieved for the samples compacted at 275 °C under 7.7 GPa (which resulted in an amorphous bulk) and nanocrystallised at 235 °C for 20 min. Another group of the produced materials were bulk nanocrystalline Al-Si-(Ni,Fe)-Mm alloys obtained by ball-milling of nanocrystalline ribbons and consolidation. The hardness of these samples achieved the value five times higher (350HV) than that of commercial 4xxx series Al alloys. Nanocrystalline Al-based alloys were also prepared by mechanical alloying followed by hot-pressing. In this group of materials, there were Al-Fe alloys containing 50-85 at.% of Al and ternary or quaternary Al-Fe-(Ti, Si, Ni, Mg, B) alloys. Microhardness of these alloys was in the range of 613 - 1235 HV0.2, depending on the composition.

  10. Steam Oxidation Behavior of Advanced Steels and Ni-Based Alloys at 800 °C

    NASA Astrophysics Data System (ADS)

    Dudziak, T.; Boroń, L.; Deodeshmukh, V.; Sobczak, J.; Sobczak, N.; Witkowska, M.; Ratuszek, W.; Chruściel, K.

    2017-03-01

    This publication studies the steam oxidation behavior of advanced steels (309S, 310S and HR3C) and Ni-based alloys (Haynes® 230®, alloy 263, alloy 617 and Haynes® 282®) exposed at 800 °C for 2000 h under 1 bar pressure, in a pure water steam system. The results revealed that all exposed materials showed relatively low weight gain, with no spallation of the oxide scale within the 2000 h of exposure. XRD analysis showed that Ni-based alloys developed an oxide scale consisting of four main phases: Cr2O3 (alloy 617, Haynes® 282®, alloy 263 and Haynes® 230®), MnCr2O4 (alloy 617, Haynes® 282® and Haynes® 230®), NiCr2O4 (alloy 617) and TiO2 (alloy 263, Haynes® 282®). In contrast, advanced steels showed the development of Cr2O3, MnCr2O4, Mn7SiO12, FeMn(SiO4) and SiO2 phases. The steel with the highest Cr content showed the formation of Fe3O4 and the thickest oxide scale.

  11. Colorimetric analysis of opaque porcelain fired to different base metal alloys used in metal ceramic restorations.

    PubMed

    Ozcelik, Tuncer Burak; Yilmaz, Burak; Ozcan, Isil; Kircelli, Cem

    2008-03-01

    The popularity of base metal alloys has considerably increased in recent years because of their superior mechanical properties as well as the high cost of noble alloys. However, there is disagreement about their effect on the opaque porcelain color and the color differences among base metal alloys. The purpose of this in vitro study was to determine and compare the influence of various commercially available base metal alloys (excluding titanium-based systems) on the resulting color of opaque porcelain with the use of a colorimetric device. Fourteen different types of Ni-Cr and 3 different types of Co-Cr porcelain bonding alloys were selected with a Au-Pd alloy (V-Delta SF) as the control group for colorimetric measurements and determination of color shift after opaque application. Shade B1 of an opaque porcelain (IPS d.SIGN Opaquer) was applied (0.1 mm) to all specimens (16 mm x 1 mm). The color coordinates of each specimen were measured with a chromameter. The data were displayed in L*, a*, and b* values according to the CIELAB system, and the color differences (DeltaE) between base metal alloys and the control group were calculated. Data were statistically analyzed with 1-way ANOVA (alpha=.05). The ANOVA was followed by Dunnett's multiple comparison test for comparisons with the control group to determine specifically which groups were significantly different from the control group. The L* value of only 1 base metal alloy was significantly different from the control group (P<.001). All base metal alloy groups except 3 had a* values which were significantly different from the control group a* value (P=.001 for Rexillium III, P=.008 for Heracles N, and P<.001 for the remaining 12 alloys), whereas only 3 base metal alloys were not statistically significantly different from the control group in the means of b* values (P<.001). All base metal alloys to which opaque porcelain was applied had significantly different DeltaE values in comparison with the control group (P

  12. Corrosion resistance and electrochemical potentiokinetic reactivation testing of some iron-base hardfacing alloys

    SciTech Connect

    Cockeram, B.V.

    1999-11-01

    Hardfacing alloys are weld deposited on a base material to provide a wear resistant surface. Commercially available iron-base hardfacing alloys are being evaluated for replacement of cobalt-base alloys to reduce nuclear plant activation levels. Corrosion testing was used to evaluate the corrosion resistance of several iron-base hardfacing alloys in highly oxygenated environments. The corrosion test results indicate that iron-base hardfacing alloys in the as-deposited condition have acceptable corrosion resistance when the chromium to carbon ratio is greater than 4. Tristelle 5183, with a high niobium (stabilizer) content, did not follow this trend due to precipitation of niobium-rich carbides instead of chromium-rich carbides. This result indicates that iron-base hardfacing alloys containing high stabilizer contents may possess good corrosion resistance with Cr:C < 4. NOREM 02, NOREM 01, and NoCo-M2 hardfacing alloys had acceptable corrosion resistance in the as-deposited and 885 C/4 hour heat treated condition, but rusting from sensitization was observed in the 621 C/6 hour heat treated condition. The feasibility of using an Electrochemical Potentiokinetic Reactivation (EPR) test method, such as used for stainless steel, to detect sensitization in iron-base hardfacing alloys was evaluated. A single loop-EPR method was found to provide a more consistent measurement of sensitization than a double loop-EPR method. The high carbon content that is needed for a wear resistant hardfacing alloy produces a high volume fraction of chromium-rich carbides that are attacked during EPR testing. This results in inherently lower sensitivity for detection of a sensitized iron-base hardfacing alloy than stainless steel using conventional EPR test methods.

  13. Elevated temperature fretting fatigue of nickel based alloys

    NASA Astrophysics Data System (ADS)

    Gean, Matthew C.

    This document details the high temperature fretting fatigue of high temperature nickel based alloys common to turbine disk and blade applications. The research consists of three area of focus: Experiments are conducted to determine quantitatively the fretting fatigue lives of advanced nickel based alloys; Analytical tools are developed and used to investigate the fretting fatigue response of the material; Fractographic analysis of the experimental results is used to improve the analytical models employed in the analysis of the experiments. Sixty three fretting fatigue experiments were conducted at 649 °C using a polycrystalline Nickel specimen in contact with directionally solidified and single crystal Nickel pads. Various influences on the fretting fatigue life are investigated. Shot peened Rene' 95 had better fretting fatigue life compared to shot peened Rene' 88. Shot peening produced a 2x increase in life for Rene' 95, but only a marginal improvement in the fretting fatigue life for Rene' 88. Minor cycles in variable amplitude loading produces significant damage to the specimen. Addition of occasional overpeaks in load produces improvements in fretting fatigue life. Contact tractions and stresses are obtained through a variety of available tools. The contact tractions can be efficiently obtained for limited geometries, while FEM can provide the contact tractions for a broader class of problems, but with the cost of increased CPU requirements. Similarly, the subsurface contact stresses can be obtained using the contact tractions as a boundary condition with either a semi-analytical FFT method or FEM. It is found that to calculate contact stresses the FFT was only marginally faster than FEM. The experimental results are combined with the analysis to produce tools that are used to design against fretting fatigue. Fractographic analysis of the fracture surface indicates the nature of the fretting fatigue crack behavior. Interrupted tests were performed to analyze

  14. Thermophysical Properties of Liquid AlTi-Based Alloys

    NASA Astrophysics Data System (ADS)

    Egry, I.; Holland-Moritz, D.; Novakovic, R.; Ricci, E.; Wunderlich, R.; Sobczak, N.

    2010-05-01

    The surface tension and density of three liquid AlTi-based alloys (AlTiV, AlTiNb, and AlTiTa) have been measured using electromagnetic levitation as a tool for containerless processing. Surface tension has been determined by the oscillating-drop method, while the density was measured using a shadowgraph technique. Both quantities were determined over a wide temperature range, including the undercooled regime. In addition, sessile-drop and pendant-drop experiments to determine the surface tension were performed in a recently built high-temperature furnace. The measured data were compared to thermodynamic calculations using phenomenological models and the Butler equation. Generally, good agreement was found.

  15. Welding of NOREM iron-base hardfacing alloy wire products: Procedures for gas tungsten arc welding

    SciTech Connect

    Phillps, M.K.; Findlan, S.J. . Nondestructive Evaluation Center)

    1992-09-01

    New wire products have been successfully fabricated and procedures developed for automatic gas tungsten arc welding of wear-resistant NOREM iron-base alloys. Research demonstrated that sound multilayer welds on carbon and stainless steel substrates can be obtained without the use of preheating. These developments point to the advantages of NOREM alloys for field applications, such as valve refurbishing.

  16. Modern Refractory Alloys Based on Titanium Gamma-Aluminide: Prospects of Development and Application

    NASA Astrophysics Data System (ADS)

    Nochovnaya, N. A.; Panin, P. V.; Kochetkov, A. S.; Bokov, K. A.

    2014-11-01

    The recent scientific and engineering level of refractory intermetallic alloys based on equiatomic titanium gamma-aluminide (TiAl) for aircraft engines and power plants is reviewed. The main tendencies and prospects of development of such alloys, processes of their production and treatment are described.

  17. Steam reforming of ethanol for hydrogen production over Cu/Co-Mg-Al-based catalysts prepared by hydrotalcite route.

    PubMed

    Homsi, Doris; Rached, Jihane Abou; Aouad, Samer; Gennequin, Cédric; Dahdah, Eliane; Estephane, Jane; Tidahy, Haingomalala Lucette; Aboukaïs, Antoine; Abi-Aad, Edmond

    2017-04-01

    The performances of different 5Cu/CoxMg6-xAl2 (x = 0; 2; 4; 6) catalysts prepared by the wet impregnation method were investigated in the ethanol steam-reforming reaction (ESR) at 450 °C during 4 h under a steam/ethanol ratio of 3 (S/E = 3). The best catalyst among the prepared solids was 5Cu/Co6Al2 as it showed a complete ethanol conversion and the highest hydrogen and carbon dioxide productivities. However, following 50 h of aging, the catalyst deactivated due to the formation of a high amount of carbonaceous products detected by differential scanning calorimetry/thermogravimetry. On the other hand, the 5Cu/Co2Mg4Al2 catalyst showed a much lower quantity of coke deposition with no deactivation due to the basic character conferred by the magnesium oxide phase.

  18. Processing of New Materials by Additive Manufacturing: Iron-Based Alloys Containing Silver for Biomedical Applications

    NASA Astrophysics Data System (ADS)

    Niendorf, Thomas; Brenne, Florian; Hoyer, Peter; Schwarze, Dieter; Schaper, Mirko; Grothe, Richard; Wiesener, Markus; Grundmeier, Guido; Maier, Hans Jürgen

    2015-07-01

    In the biomedical sector, production of bioresorbable implants remains challenging due to improper dissolution rates or deficient strength of many candidate alloys. Promising materials for overcoming the prevalent drawbacks are iron-based alloys containing silver. However, due to immiscibility of iron and silver these alloys cannot be manufactured based on conventional processing routes. In this study, iron-manganese-silver alloys were for the first time synthesized by means of additive manufacturing. Based on combined mechanical, microscopic, and electrochemical studies, it is shown that silver particles well distributed in the matrix can be obtained, leading to cathodic sites in the composite material. Eventually, this results in an increased dissolution rate of the alloy. Stress-strain curves showed that the incorporation of silver barely affects the mechanical properties.

  19. Synthesis of a novel layered double hydroxides [MgAl(4)(OH)(12)](Cl)(2)·2.4H(2)O and its anion-exchange properties.

    PubMed

    Chitrakar, Ramesh; Makita, Yoji; Sonoda, Akinari; Hirotsu, Takahiro

    2011-01-30

    A novel layered double hydroxide of Mg and Al with composition [Mg(0.96)Al(4.00)(OH)(12)]Cl(1.86)(CO(3))(0.03)·2.4H(2)O, designated as MgAl(4)-Cl, was synthesized by mixing crystalline gibbsite (γ-Al(OH)(3)) and solid MgCl(2)·6H(2)O with subsequent hydrothermal treatment at 160 °C for 72h. The MgAl(4)-Cl exhibited a crystalline material of a layered structure, as evidenced from X-ray diffraction. Anion uptake experiments with the MgAl(4)-Cl showed that Cl(-) in the interlayer space can be exchanged with anions such as Br(-), H(2)PO(4)(-), CO(3)(2-) or dodecyl sulfate (DS(-)) from aqueous solutions with preservation of the layered structure. Uptake of NO(3)(-), BrO(3)(-) or SO(4)(2-) on the MgAl(4)-Cl showed different behavior; these anions can be exchanged within 1h maintaining the layered structure, but a release of Mg(2+) cations from the sample was observed with increased reaction time, resulting in collapse of the layered structure and formation of the gibbsite phase, as determined from chemical analyses and X-ray diffraction. Copyright © 2010 Elsevier B.V. All rights reserved.

  20. Synthesis and adsorption properties of nanosized Mg-Al layered double hydroxides with Cl-, NO{3/-} or SO{4/2-} as interlayer anion

    NASA Astrophysics Data System (ADS)

    Hongo, T.; Wakasa, H.; Yamazaki, A.

    2011-06-01

    Nanosized Mg-Al layered double hydroxides (LDHs) with Cl-, NO{3/-} or SO{4/2-} as the interlayer anion have been synthesized by a modified coprecipitation method. The obtained LDHs were confirmed to be composed of a single phase and to be highly substituted by Al (Mg/Al ratio ˜1.9). The abilities of the LDHs to adsorb several harmful anions (F-, CrO{4/2-}, HAsO{4/2-} and HSeO3-) in aqueous solution were studied. The LDHs exhibit high adsorption abilities. The amount of adsorption onto the LDHs differed between the starting interlayer anions, and decreased in the following order of the interlayer anions: NO{3/-} > Cl- > SO{4/2-}. The NO3-formed Mg-Al LDH reached a CrO{4/2-} adsorption equilibrium state within only 30 min, much faster than those in previous reports. Thus, the nanocrystallized, highly Al substituted phase of the NO3-formed Mg-Al LDH is found to markedly enhance the anion adsorption ability.

  1. Nanohybrids of Mg/Al layered double hydroxide and long-chain (C18) unsaturated fatty acid anions: Structure and sorptive properties

    USDA-ARS?s Scientific Manuscript database

    Long-chain (C18) unsaturated fatty acid anions, elaidate (ELA), oleate (OLE), linoleate (LINO), and linolenate (LINOLEN), were intercalated into Mg/Al (3:1) layered double hydroxide (LDH) and the resultant organo-LDH nanohybrid materials were characterized and subsequently evaluated as sorbents of s...

  2. Comparative study of Mg/Al- and Zn/Al-layered double hydroxide-perindopril erbumine nanocomposites for inhibition of angiotensin-converting enzyme

    PubMed Central

    Hussein Al Ali, Samer Hasan; Al-Qubaisi, Mothanna; Hussein, Mohd Zobir; Ismail, Maznah; Zainal, Zulkarnain; Hakim, Muhammad Nazrul

    2012-01-01

    The intercalation of a drug active, perindopril, into Mg/Al-layered double hydroxide for the formation of a new nanocomposite, PMAE, was accomplished using a simple ion exchange technique. A relatively high loading percentage of perindopril of about 36.5% (w/w) indicates that intercalation of the active took place in the Mg/Al inorganic interlayer. Intercalation was further supported by Fourier transform infrared spectroscopy, and thermal analysis shows markedly enhanced thermal stability of the active. The release of perindopril from the nanocomposite occurred in a controlled manner governed by pseudo-second order kinetics. MTT assay showed no cytotoxicity effects from either Mg/Al-layered double hydroxide or its nanocomposite, PMAE. Mg/Al-layered double hydroxide showed angiotensin-converting enzyme inhibitory activity, with 5.6% inhibition after 90 minutes of incubation. On incubation of angiotensin-converting enzyme with 0.5 μg/mL of the PMAE nanocomposite, inhibition of the enzyme increased from 56.6% to 70.6% at 30 and 90 minutes, respectively. These results are comparable with data reported in the literature for Zn/Al-perindopril. PMID:22904631

  3. Comparative study of Mg/Al- and Zn/Al-layered double hydroxide-perindopril erbumine nanocomposites for inhibition of angiotensin-converting enzyme.

    PubMed

    Hussein Al Ali, Samer Hasan; Al-Qubaisi, Mothanna; Hussein, Mohd Zobir; Ismail, Maznah; Zainal, Zulkarnain; Hakim, Muhammad Nazrul

    2012-01-01

    The intercalation of a drug active, perindopril, into Mg/Al-layered double hydroxide for the formation of a new nanocomposite, PMAE, was accomplished using a simple ion exchange technique. A relatively high loading percentage of perindopril of about 36.5% (w/w) indicates that intercalation of the active took place in the Mg/Al inorganic interlayer. Intercalation was further supported by Fourier transform infrared spectroscopy, and thermal analysis shows markedly enhanced thermal stability of the active. The release of perindopril from the nanocomposite occurred in a controlled manner governed by pseudo-second order kinetics. MTT assay showed no cytotoxicity effects from either Mg/Al-layered double hydroxide or its nanocomposite, PMAE. Mg/Al-layered double hydroxide showed angiotensin-converting enzyme inhibitory activity, with 5.6% inhibition after 90 minutes of incubation. On incubation of angiotensin-converting enzyme with 0.5 μg/mL of the PMAE nanocomposite, inhibition of the enzyme increased from 56.6% to 70.6% at 30 and 90 minutes, respectively. These results are comparable with data reported in the literature for Zn/Al-perindopril.

  4. Effect of intercalated aromatic sulfonates on uptake of aromatic compounds from aqueous solutions by modified Mg-Al layered double hydroxide

    SciTech Connect

    Kameda, Tomohito; Yamazaki, Takashi; Yoshioka, Toshiaki

    2010-06-15

    In this study, we utilized Mg-Al layered double hydroxide (Mg-Al LDH) modified by intercalation with three aromatic sulfonates-2,7-naphthalene disulfonate (2,7-NDS{sup 2-}), benzenesulfonate (BS{sup -}), and benzenedisulfonate (BDS{sup 2-})-for the uptake of two aromatics-1,3-dinitrobenzene (DNB) and anisole (AS)-from aqueous solution and determined the effect of the aromatic sulfonates on the uptake of these aromatics. We found that the electron-rich aromatic ring of the intercalated aromatic sulfonates such as 2,7-NDS{sup 2-} undergoes strong {pi}-{pi} stacking interactions with the electron-poorer benzene ring of DNB in aqueous solution, and these interactions result in a higher uptake of DNB by the modified Mg-Al LDHs. In contrast, the electron-poor aromatic ring of the aromatic sulfonates such as BDS{sup 2-} undergoes weak {pi}-{pi} stacking interactions with the electron-poorer benzene ring of DNB, and these interactions result in a lower uptake of DNB by the modified Mg-Al LDHs.

  5. Pore Formation Upon Nitriding Iron and Iron-Based Alloys: The Role of Alloying Elements and Grain Boundaries

    NASA Astrophysics Data System (ADS)

    Schwarz, B.; Göhring, H.; Meka, S. R.; Schacherl, R. E.; Mittemeijer, E. J.

    2014-12-01

    Pure iron and a series of iron-based Fe-Me alloys (with Me = Al, Si, Cr, Co, Ni, and Ge) were nitrided in a NH3/H2 gas mixture at 923 K (650 °C). Different nitriding potentials were applied to investigate the development of pores under ferrite and austenite stabilizing conditions. In all cases, pores developed in the nitrided microstructure, i.e., also and strikingly pure ferritic iron exhibited pore development. The pore development is shown to be caused by the decomposition of (homogeneous) nitrogen-rich Fe(-Me)-N phase into nitrogen-depleted Fe(-Me)-N phase and molecular N2 gas. The latter, gas phase can be associated with such high pressure that the surrounding iron-based matrix can yield. Thermodynamic assessments indicate that continued decomposition, i.e., beyond the state where yielding is initiated, is possible. Precipitating alloying-element nitrides, i.e., AlN, CrN, or Si3N4, in the diffusion zone below the surface, hinder the formation of pores due to the competition of alloying-element nitride (Me x N y ) precipitation and pore (N2) development; alloying elements reducing the solubility of nitrogen enhance pore formation. No pore formation was observed upon nitriding a single crystalline pure iron specimen, nitrided under ferrite stabilizing conditions, thereby exhibiting the essential function of grain boundaries for nucleation of pores.

  6. Friction and wear of iron-base binary alloys in sliding contact with silicon carbide in vacuum

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1980-01-01

    Multipass sliding friction experiments were conducted with various iron base binary alloys in contact with a single crystal silicon carbide surface in vacuum. Results indicate that the atomic size and concentration of alloy elements play important roles in controlling the transfer and friction properties of iron base binary alloys. Alloys having high solute concentration produce more transfer than do alloys having low solute concentration. The coefficient of friction during multipass sliding generally increases with an increase in the concentration of alloying element. The change of friction with succeeding passes after the initial pass also increases as the solute to iron, atomic radius ratio increases or decreases from unity.

  7. Band gaps by design: Tailoring ZnO based semiconductor alloy films

    NASA Astrophysics Data System (ADS)

    Che, Hui

    This dissertation presents the research on the synthesis of ZnO based ternary semiconductor alloy films with tailored band gaps and the studies in their structural and optical properties. MgxZn1-xO alloys expanded the band gaps from 3.20 eV to deeper UV region of 5.67 eV. While ZnSxO1-x reduced the band gaps into the visible region of 2.9 eV. The alloy films were grown via reactive sputtering deposition, which is a cost effective and environment-friendly technique. An analytical method was developed for accurately determining the band gaps of alloys via transmission spectroscopy. The structural inhomogeneity issues in the Mg xZn1-xO alloys were studied via Selective Resonant Raman Scattering. Urbach energy analysis and Raman spectral line width analysis indicated that structural defects and alloy composition fluctuations in the MgxZn1-xO alloy films are the dominant origins of the localized electronic tail states and the Raman line broadening. While the Raman line broadening due to the anharmonicity of the alloys is not significant. The achievement of ZnSxO1-x alloy films with reduced band gaps paved the way for further research on band gap engineering of ZnO in the visible region.

  8. 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.

  9. Influence of S. mutans on base-metal dental casting alloy toxicity.

    PubMed

    McGinley, E L; Dowling, A H; Moran, G P; Fleming, G J P

    2013-01-01

    We have highlighted that exposure of base-metal dental casting alloys to the acidogenic bacterium Streptococcus mutans significantly increases cellular toxicity following exposure to immortalized human TR146 oral keratinocytes. With Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), S. mutans-treated nickel-based (Ni-based) and cobalt-chromium-based (Co-Cr-based) dental casting alloys were shown to leach elevated levels of metal ions compared with untreated dental casting alloys. We targeted several biological parameters: cell morphology, viable cell counts, cell metabolic activity, cell toxicity, and inflammatory cytokine expression. S. mutans-treated dental casting alloys disrupted cell morphology, elicited significantly decreased viable cell counts (p < 0.0001) and cell metabolic activity (p < 0.0001), and significantly increased cell toxicity (p < 0.0001) and inflammatory cytokine expression (p < 0.0001). S. mutans-treated Ni-based dental casting alloys induced elevated levels of cellular toxicity compared with S. mutans-treated Co-Cr-based dental casting alloys. While our findings indicated that the exacerbated release of metal ions from S. mutans-treated base-metal dental casting alloys was the likely result of the pH reduction during S. mutans growth, the exact nature of mechanisms leading to accelerated dissolution of alloy-discs is not yet fully understood. Given the predominance of S. mutans oral carriage and the exacerbated cytotoxicity observed in TR146 cells following exposure to S. mutans-treated base-metal dental casting alloys, the implications for the long-term stability of base-metal dental restorations in the oral cavity are a cause for concern.

  10. Biodegradability and platelets adhesion assessment of magnesium-based alloys using a microfluidic system.

    PubMed

    Liu, Lumei; Koo, Youngmi; Collins, Boyce; Xu, Zhigang; Sankar, Jagannathan; Yun, Yeoheung

    2017-01-01

    Magnesium (Mg)-based stents are extensively explored to alleviate atherosclerosis due to their biodegradability and relative hemocompatibility. To ensure the quality, safety and cost-efficacy of bioresorbable scaffolds and full utilization of the material tunability afforded by alloying, it is critical to access degradability and thrombosis potential of Mg-based alloys using improved in vitro models that mimic as closely as possible the in vivo microenvironment. In this study, we investigated biodegradation and initial thrombogenic behavior of Mg-based alloys at the interface between Mg alloys' surface and simulated physiological environment using a microfluidic system. The degradation properties of Mg-based alloys WE43, AZ31, ZWEK-L, and ZWEK-C were evaluated in complete culture medium and their thrombosis potentials in platelet rich plasma, respectively. The results show that 1) physiological shear stress increased the corrosion rate and decreased platelets adhesion rate as compared to static immersion; 2) secondary phases and impurities in material composition induced galvanic corrosion, resulting in higher corrosion resistance and platelet adhesion rate; 3) Mg-based alloys with higher corrosion rate showed higher platelets adhesion rate. We conclude that a microfluidic-based in vitro system allows evaluation of biodegradation behaviors and platelets responses of Mg-based alloys under specific shear stress, and degradability is related to platelets adhesion.

  11. Creep-Rupture Behavior of Ni-Based Alloy Tube Bends for A-USC Boilers

    NASA Astrophysics Data System (ADS)

    Shingledecker, John

    Advanced ultrasupercritical (A-USC) boiler designs will require the use of nickel-based alloys for superheaters and reheaters and thus tube bending will be required. The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section II PG-19 limits the amount of cold-strain for boiler tube bends for austenitic materials. In this summary and analysis of research conducted to date, a number of candidate nickel-based A-USC alloys were evaluated. These alloys include alloy 230, alloy 617, and Inconel 740/740H. Uniaxial creep and novel structural tests and corresponding post-test analysis, which included physical measurements, simplified analytical analysis, and detailed microscopy, showed that different damage mechanisms may operate based on test conditions, alloy, and cold-strain levels. Overall, creep strength and ductility were reduced in all the alloys, but the degree of degradation varied substantially. The results support the current cold-strain limits now incorporated in ASME for these alloys for long-term A-USC boiler service.

  12. NEUTRON REACTOR FUEL ELEMENT UTILIZING ZIRCONIUM-BASE ALLOYS

    DOEpatents

    Saller, H.A.; Keeler, J.R.; Szumachowski, E.R.

    1957-11-12

    This patent relates to clad fuel elements for use in neutronic reactors and is drawn to such a fuel element which consists of a core of fissionable material, comprised of an alloy of zirconium and U/sup 235/ enriched uranium, encased in a jacket of a binary zirconium-tin alloy in which the tin content ranges between 1 and 15% by weight.

  13. Modifying ability of titanium-based pelleted master alloys

    NASA Astrophysics Data System (ADS)

    Bazhin, V. Yu.; Savchenkov, S. A.; Kosov, Ya. I.

    2017-05-01

    The problem of enhancing the quality of pressed titanium master alloys is discussed to increase the rate and degree of dissolution of their components and to ensure the formation of a fine-grained structure in aluminum alloys. A technology of producing a pelleted titanium master alloy for effective correction of the chemical composition of an aluminum alloy in casting is developed and tested. Incoming inspection of the component composition and the flux distribution in the volume of pressed pellets of various manufacturers is performed. The rate of dissolution of pressed powder master alloys in the aluminum melt is studied, and their modifying ability is estimated after studying the microstructures of cast blanks. Molasses is used as a binder in a pelleted master alloy. As a result, we achieved a uniform flux distribution over the pellet volume and the formation of uniform pores after annealing as compared pelleted master alloys of other manufacturers. The fabricated alloying briquettes have higher strength characteristics and their dissolution rate in the aluminum melt is higher than those of analogs by 15-20%.

  14. Cerium-based conversion coatings on magnesium alloys

    NASA Astrophysics Data System (ADS)

    Castano Londono, Carlos Eduardo

    This research is primarily focused on gaining a better understanding of the deposition and corrosion behavior of cerium-based conversion coatings (CeCCs) on AZ31B and AZ91D Mg alloys. Deposition of homogenous and protective CeCCs was highly dependent on the surface preparation steps. The best results were obtained when Mg samples underwent grinding, acid cleaning, and alkaline cleaning processes. This reduced the number of active cathodic sites and promoted the formation of a protective Al-rich Mg oxide/hydroxide layer. Electrochemical properties of the CeCCs were also strongly correlated with morphological, microstructural, and chemical characteristics. Protective CeCCs were deposited on both AZ31 and AZ91 Mg alloys using a range of deposition times (5 to 180 s) and temperatures (10 to 80 °C). However, shorter deposition times (5 s) and lower deposition temperatures (~10 °C) showed higher impedance and longer bath stability than other deposition conditions. The increase in impedance was related with fewer cracks and smaller nodule sizes. Additional investigations of post-treated CeCCs exposed to NaCl environments showed an increased in the total impedance. The increase in corrosion protection of the CeCCs was associated with an overall increase in coating thickness from 400 to 800 nm. A microstructural evolution from ~3 nm nodular nanocrystals of CeO2/CePO4*H2O embedded in an amorphous matrix to >50 nm CePO4*H2O nanocrystals was responsible for the electrochemically active corrosion protection. Exposure of CeCCs to sunlight in humid environments promoted the reduction of Ce(IV) into Ce(III) species compared to unexposed coatings. This reduction process was related with photocatalytic water oxidation reaction.

  15. Infection free titanium alloys by stabile thiol based nanocoating.

    PubMed

    Cökeliler, Dilek; Göktaş, Hilal; Tosun, Pinar Deniz; Mutlu, Selma

    2010-04-01

    As biomedical materials, titanium and titanium alloys (Ti-6Al-4V) are superior to many materials in terms of mechanical properties and biocompatibility. However, they are still not sufficient for prolonged clinical use because the biocompatibility of these materials must be improved. In this study, the prevention of the attachment of test microorganism on the Ti alloy surfaces by thiol (-SH) and hydroxyl (-OH) functional group containing monomer in plasma based electron beam generator was reported in order to prepare anti-fouling surfaces. The precursor, 11-mercaptoundecanoic acid is used as plasma source to create nano-film with 30-60 nm approximately. The surface chemistry and topology of uncoated and coated samples are characterized by Fourier Transform Infrared Spectroscopy (FTIR) and Atomic Force Microscopy (AFM). Static contact angle measurements are performed to state the change of surface hydrophilicity. All coated samples are tested in-vitro environment with Staphylococcus epidermidis that is chosen as the test bacteria strain in view of its significance for the pathogenesis of medical-device-related infections. This test is repeated after certain period of times and samples are waited in dynamic fluid media in order to investigate the stability of nano-coating. Plasma polymerized 11-mercaptoundecanoic acid film (PP MUA) with 42 +/- 4 nm is found alternative, stabile and simple method to create bacterial anti-fouling surfaces. The static contact angle of the coated surface is 34 +/- 80 whereas the uncoated surface is 57 +/- 50. For the coated surface, the presence of C-OH and C==O groups in infrared spectra defining the PP MUA is achieved by the plasma polymerization. The attachment of the model microorganism on the biomaterial surface prepared by PP MUA is reduced 85.3% if compared to unmodified control surface.

  16. Design and characterization of a novel nickel-free cobalt-base alloy for intravascular stents.

    PubMed

    Wang, Qiang; Ren, Yibin; Babar Shahzad, M; Zhang, Wei; Pan, Xumeng; Zhang, Song; Zhang, Dan

    2017-08-01

    Co-Cr-W-Ni alloy (L605) with high tensile strength is used in coronary stents. The thickness of individual strut of the stent is reduced which can decrease the stent restenosis rate. However, about 10% Ni element content in L605 is found to cause allergic reactions and pulmonary embolism, similar to the traditional 316L stainless steel. In this study, a novel nickel-free cobalt-base alloy Co-20Cr-12Fe-18Mn-2Mo-4W-N (wt%) was designed and fabricated in order to efficiently avoid the potential hazards of Ni element. Fe and Mn, essential elements of human body, were added in the alloy to substitute part of Co element. In comparison to L605 alloy, the tensile strength of the new alloy was higher than 1000MPa while elongation was above 55%. The pitting potential of the new alloy was measured close to 1000mV, also higher than that of L605 alloy. CCK-8 test indicated that the cytotoxicity of the new alloy is grade 1, reflecting that Co-20Cr-12Fe-18Mn-2Mo-4W-N alloy has no cytotoxic effects. There was no significant difference in the apoptosis rates between Co-20Cr-12Fe-18Mn-2Mo-4W-N and L605 alloy. The newly developed cobalt-base alloy showed excellent mechanical, corrosion resistance and biological properties, which could make it a desirable material for future clinical investigations. Copyright © 2017 Elsevier B.V. All rights reserved.

  17. Scale formation on Ni-based alloys in simulated solid oxide fuel cell interconnect environments

    SciTech Connect

    Ziomek-Moroz, Margaret; Cramer, Stephen D.; Holcomb, Gordon R.; Covino, Bernard S., Jr.; Bullard, Sophie J.; Singh, P.; Windisch, C.F.; Johnson, C.D.; Schaeffer, C.

    2004-11-01

    Recent publications suggest that the environment on the fuel side of the bi-polar stainless steel SOFC interconnects changes the oxidation behavior and morphology of the scale formed on the air side. The U.S. Department of Energy Albany Research Center (ARC), has examined the role of such exposure conditions on advanced nickel base alloys. Alloy formulations developed at ARC and commercial alloys were studied using X-ray diffraction (XRD) and Raman spectroscopy. The electrical property of oxide scales formed on selected alloys was determined in terms of areaspecific resistance (ASR). The corrosion behavior of ARC nickel-based alloys exposed to a dual environment of air/ H2 were compared to those of Crofer 22APU and Haynes 230.

  18. Cr{sub 2}Nb-based alloy development

    SciTech Connect

    Liu, C.T.; Horton, J.A.; Carmichael, C.A.

    1996-05-01

    This paper summarizes recent progress in developing Cr{sub 2}Nb/Cr(Nb) alloys for structural use in advanced fossil energy conversion systems. Alloy additions were added to control the microstructure and mechanical properties. Two beneficial elements have been identified among all alloying additions added to the alloys. One element is effective in refining the coarse eutectic structure and thus substantially improves the compressive strength and ductility of the alloys. The other element enhances oxidation resistance without sacrificing the ductility. The tensile properties are sensitive to cast defects, which can not be effectively reduced by HIPping at 1450-1580{degrees}C and/or directionally solidifying via a floating zone remelting method.

  19. Development and study of chemical vapor deposited tantalum base alloys

    NASA Technical Reports Server (NTRS)

    Meier, G. H.; Bryant, W. A.

    1976-01-01

    A technique for the chemical vapor deposition of alloys was developed. The process, termed pulsing, involves the periodic injection of reactant gases into a previously-evacuated reaction chamber where they blanket the substrate almost instantaneously. Formation of alternating layers of the alloy components and subsequent homogenization allows the formation of an alloy of uniform composition with the composition being determined by the duration and relative numbers of the various cycles. The technique has been utilized to produce dense alloys of uniform thickness and composition (Ta- 10 wt % W) by depositing alternating layers of Ta and W by the hydrogen reduction of TaCl5 and WCl6. A similar attempt to deposit a Ta - 8 wt % W - 2 wt% Hf alloy was unsuccessful because of the difficulty in reducing HfCl4 at temperatures below those at which gas phase nucleation of Ta and W occurred.

  20. The erosion-corrosion of copper-based and nickel-based alloys in warm polluted Arabian Gulf seawater

    SciTech Connect

    Carew, J.A.; Islam, M.

    1994-12-31

    This paper presents the results of an investigation of the erosion-corrosion behavior of copper-nickel alloys (90:10 Cu/Ni and 7030 Cu/Ni), nickel-copper alloy UNS N04400 and nickel-based alloys (UNS N06022, N06030 and UNS S32550) used as heat exchanger tubes, in warm flowing Arabian Gulf seawater containing up to 5 ppm of sulphide ions. Visual and optical examinations of the internal surfaces of the tubes were carried out to compare the susceptibilities to erosion-corrosion attack of the different alloys, taking into consideration the nature of the product films formed.

  1. Performance of Alumina-Forming Austenitic Steels, Fe-base and Ni-base alloys exposed to metal dusting environments

    SciTech Connect

    Vande Put Ep Rouaix, Aurelie; Unocic, Kinga A; Pint, Bruce A; Brady, Michael P

    2011-01-01

    A series of conventional Fe- and Ni- base, chromia- and alumina- forming alloys, and a newly developed creep-resistant, alumina-forming austenitic steel were developed and its performance relative to conventional Fe- and Ni-based chromia-forming alloys was evaluated in metal dusting environments with a range of water vapor contents. Five 500h experiments have been performed at 650 C with different water vapor contents and total pressures. Without water vapor, the Ni-base alloys showed greater resistance to metal dusting than the Fe-base alloys, including AFA. However, with 10-28% water vapor, more protective behavior was observed with the higher-alloyed materials and only small mass changes were observed. Longer exposure times are in progress to further differentiate performance.

  2. Processing and Characterization of Mechanically Alloyed NiAl-Based Alloys

    DTIC Science & Technology

    1994-07-20

    34 69OSW *MN. VU e ffo Qm .’so~ W&84" ow" ftawm pl "-wtvý a " M Wc rmsa I. XUR On GELs"NW REORT oIt3.RPOT rVPE AND CAT93 CoVWau July 20, 1994 ’ Fin l Report...SUPPUMWRNTY MOTUS 12a. OMT-U.IOUI AVAIAAJT STAT1[MET 13. OGTFM-1NO Co Unlimited WLA8ETRACT (Mainuna 2O00nw m Mechanical alloying of powders followed by hot...present materials result from their unique microstructure. = 14• TIS. M OF PAGES Mechanical Alloying, NiAl-Aluminides, Intermetallics Strength

  3. Spectroscopic study and enhanced thermostability of combustion-derived BaMgAl10O17:Eu2+ blue phosphors for solid-state lighting

    NASA Astrophysics Data System (ADS)

    Pradal, Nathalie; Potdevin, Audrey; Chadeyron, Geneviève; Bonville, Pierre; Caillier, Bruno; Mahiou, Rachid

    2017-02-01

    Blue-emitting BaMgAl10O17:Eu2+ (BAM:Eu), suitable for applications in a next generation of Hg-free lamps based on UV LEDs, was prepared by a microwave induced solution combustion synthesis, using urea as combustion fuel and nitrates as oxidizers. Purity control of the as-synthesized blue phosphor was undertaken by a washing step followed by a reduction one. Structural and morphological properties of the outcoming phosphors have been considered. Synthesis process allows producing a well-crystallized and nanostructured BAM phase within only few minutes. The influence of reduction treatment on the relative amounts of Eu2+/Eu3+ in our samples has been investigated through an original study by magnetization and Mössbauer spectroscopy. Furthermore, a complete optical study has been carried out and allowed us to determine the europium localization in the three possible sites in BAM matrix. The percentage of Eu2+ increased twofold after the reduction treatment, entailing an increase in the luminescence efficiency upon UV excitation. Finally, temperature-dependent luminescence of combustion-derived powders has been studied till 170 °C and compared to that of commercial BAM:Eu. MISCS-derived phosphors present a higher thermal stability than commercial one: whereas the emission efficiency of this last was reduced by 64%, the one of combustion-derived BAM:Eu experienced an only 12% decline. Furthermore, while commercial BAM suffered from a severe blue-shift with increasing temperature, our phosphors keep its color quality with a good stability of the photometric parameters.

  4. Single-crystal elastic constants of spinel (MgAl2O4) to 11.1 GPa by Brillouin scattering

    NASA Astrophysics Data System (ADS)

    Speziale, S.; Nestola, F.; Jiang, F.; Duffy, T. S.

    2016-12-01

    We have determined the pressure dependence of the full tensor of synthetic MgAl2O4 spinel by measuring Brillouin scattering from ambient pressure to 11.1 GPa at ambient temperature. The elastic stiffness coefficients of spinel at ambient conditions are C11 = 282 ± 1 GPa, C12 = 155 ± 1 GPa and C44 = 154.0 ± 0.2 GPa, and the aggregate bulk and shear modulus are KS0 = 197 ± 1 GPa and G0 = 98.3 ± 0.4 GPa. Their pressure derivatives, in the framework of third order Eulerian strain theory, are (∂C11/∂P)T0 = 4.7 ± 0.2, (∂C12/∂P)T0 = 4.5 ± 0.2, (∂C44/∂P)T0 = 1.12 ± 0.03, (∂KS/∂P)T0 = 4.5 ± 0.2, (∂G/∂P)T0 = 0.36 ± 0.06. These results are in agreement with X-ray diffraction studies, recent ab initio calculations and the majority existing experimental results based on ultrasonic techniques. The apparent inconsistency of our fitted pressure derivatives with the only previous single-crystal elasticity study conducted at similar pressure (Yoneda, 1990) is due to the different model used to fit the data. Such apparent disagreement highlights once more the non-transferability of fitted elastic parameters from one formulation of the finite strain equations to another one.

  5. Nonlocal anomalous Hall effect in ternary alloys based on noble metals

    NASA Astrophysics Data System (ADS)

    Töpler, Franziska; Hönemann, Albert; Tauber, Katarina; Fedorov, Dmitry V.; Gradhand, Martin; Mertig, Ingrid; Fert, Albert

    2016-10-01

    We present a theoretical study of the nonlocal anomalous Hall effect induced by heavy-metal impurities in dilute magnetic alloys based on noble metals. The results of our first-principles calculations are shown in comparison to those obtained within a model consideration via Matthiessen's rule. Based on the transport properties of the constituent binary alloys, we reveal optimal host-impurity combinations to enhance the phenomenon. In particular, this allows us to explain experimental findings showing a strong effect in Cu-based alloys but a vanishing effect in the case of the Au host.

  6. Solidification Behavior in Newly Designed Ni-Rich Ni-Ti-Based Alloys

    NASA Astrophysics Data System (ADS)

    Samal, Sumanta; Biswas, Krishanu; Phanikumar, Gandham

    2016-12-01

    The present investigation reports phase and microstructure evolution during solidification of novel Ni-rich Ni-Ti-based alloys, Ni60Ti40, Ni50Cu10Ti40, Ni48Cu10Co2Ti40, and Ni48Cu10Co2Ti38Ta2 during suction casting. The design philosophy of the multicomponent alloys involves judicious selection of alloying elements such as Cu, Co, and Ta in the near Ni60Ti40 eutectic alloy by replacing both Ni and Ti so that phase mixture in the microstructure remains the same from the binary to quinary alloy. The basic objective is to study the effect of addition of Cu, Co, and Ta on the phase evolution and transformation in the Ni-rich Ni-Ti-based alloys. The detailed electron microscopic studies on these suction cast alloys reveal the presence of ultrafine eutectic lamellae between NiTi and Ni3Ti phases along with dendritic NiTi and Ti2Ni phases. It has also been observed that in the binary (Ni60Ti40) alloy, the ordered NiTi (B2) phase transforms to trigonal (R) phase followed by NiTi martensitic phase (M-phase), i.e., B2 → R-phase → M-phase during solid-state cooling. However, the addition of alloying elements such as Cu, Co to the binary (Ni60Ti40) alloy suppresses the martensitic transformation of the ordered NiTi (B2) dendrite. Thus, in the ternary and quaternary alloys, the ordered NiTi (B2) phase is transformed to only trigonal (R) phase, i.e., B2 → R-phase. The secondary precipitate of Ti2Ni has been observed in all of the studied alloys. Interestingly, Ni48Cu10Co2Ti38Ta2 quinary alloy shows the disordered nature of NiTi dendrites. The experimentally observed solidification path is in good agreement with Gulliver-Scheil simulated path for binary alloy, whereas simulated solidification path deviates from the experimental results in case of ternary, quaternary, and quinary alloys.

  7. Recent progress in high Bs Fe-based nanocrystalline soft magnetic alloys

    NASA Astrophysics Data System (ADS)

    Ohta, M.; Yoshizawa, Y.

    2011-02-01

    High saturation magnetic flux density (high-Bs) alloy has been developed in an Fe-based nanocrystalline alloy system. A nanocrystalline phase with an average grain size of about 20 nm is obtained by annealing Cu-substituted and/or Cu-and-Si-complex-substituted Fe-B amorphous alloys. The alloy exhibits low coercivity of less than 7 A m-1 and a high Bs of more than 1.8 T. The iron loss at 50 Hz and 1.6 T for a toroidal core made of Fe80.5Cu1.5Si4B14 nanocrystalline alloy is 0.46 W kg-1, which is about 2/3 of that of grain-oriented Si steel. Moreover, the iron loss at 10 kHz and 0.2 T for a wound core made of this alloy is 7.5 W kg-1, which is about 25% of that of non-grain-oriented Si steel and about 60% of that of an Fe-based amorphous alloy. In addition, the cut cores made of the alloy show good superimposed dc-current characteristics and appear promising in applications such as power choke coils (at the high-frequency region).

  8. Imprecise knowledge based design and development of titanium alloys for prosthetic applications.

    PubMed

    Datta, S; Mahfouf, M; Zhang, Q; Chattopadhyay, P P; Sultana, N

    2016-01-01

    Imprecise knowledge on the composition-processing-microstructure-property correlation of titanium alloys combined with experimental data are used for developing rule based models for predicting the strength and elastic modulus of titanium alloys. The developed models are used for designing alloys suitable for orthopedic and dental applications. Reduced Space Searching Algorithm is employed for the multi-objective optimization to find composition, processing and microstructure of titanium alloys suitable for orthopedic applications. The conflicting requirements attributes of the alloys for this particular purpose are high strength with low elastic modulus, along with adequate biocompatibility and low costs. The 'Pareto' solutions developed through multi-objective optimization show that the preferred compositions for the fulfilling the above objectives lead to β or near β-alloys. The concept of decision making employed on the solutions leads to some compositions, which should provide better combination of the required attributes. The experimental development of some of the alloys has been carried out as guided by the model-based design methodology presented in this research. Primary characterizations of the alloys show encouraging results in terms of the mechanical properties.

  9. Single-Crystal Elastic Properties of the Spinel (MgAl2O4) - Galaxite (MnAl2O4) Solid Solution Series

    NASA Astrophysics Data System (ADS)

    Speziale, S.; Bruschini, E.; Andreozzi, G. B.; Bosi, F.; Hålenius, U.

    2014-12-01

    Spinels are a subject of intense research in solid state physics, materials science and geosciences. Their general formula is T(A1-i)M(AiB2-i)X4 (A and B are cations, X are anions, T and M indicate tetrahedrally- and octahedrally-coordinated sites and i is the inversion degree). They are ideal materials to study the interplay between chemical substitutions, structure and the physical properties of solids. As spinel-structured ringwoodite (Mg,Fe)2SiO4 is the most abundant mineral in the lower transition zone, understanding the effect of chemical substitution on the elastic properties of spinels is of crucial for geophysics. We have experimentally studied the variation of the elastic properties along the join MgAl2O4 - MnAl2O4. Crystals of 4 compositions along the join were synthesized at the very same experimental conditions and their crystal chemistry was fully characterized. Single-crystal elastic constants Cij of all the samples were measured by Brillouin spectroscopy at ambient conditions. For compositions with Mn/Mg < 0.5 C11 remains constant, then it decreases of ~4% for higher Mn contents. From MgAl2O4 to MnAl2O4 C12 lineraly increases ~ 5% and C44 decreases ~ 20% . The bulk modulus KS is almost constant, whereas the shear modulus G decreases ~ 18% across the join. The elastic constants of MnAl2O4 are C11 = 271.3 (± 1.3) GPa, C12 = 164.8 (± 1.3) GPa and C44 = 124.9 (5) GPa. Using the empirical polyhedral approach [1] we have inferred the effectve polyhedral bulk moduli of Mg, Mn and Al in T and M sites. We observe that KMnM < KMgM < KMgT ≈ KMnT < KAlM << KAlT. The relationship between polyhedral moduli and ionic potential IP [2] can be expressed as Ki j (GPa) = 20 ( ± 2) × IP + 108 (± 10), where i is the cation, j is the site and IP is in units of (e/Å). Using our correlation and atomic radii from [3] we successfully reproduced the bulk modulus of different oxide spinels with bi- and tri-valent cations. Our preliminary results confirm that empirical

  10. Research into Oil-based Colloidal-Graphite Lubricants for Forging of Al-based Alloys

    SciTech Connect

    Petrov, A.; Petrov, P.; Petrov, M.

    2011-05-04

    The presented paper describes the topical problem in metal forging production. It deals with the choice of an optimal lubricant for forging of Al-based alloys. Within the scope of the paper, the properties of several oil-based colloidal-graphite lubricants were investigated. The physicochemical and technological properties of these lubricants are presented. It was found that physicochemical properties of lubricant compositions have an influence on friction coefficient value and quality of forgings.The ring compression method was used to estimate the friction coefficient value. Hydraulic press was used for the test. The comparative analysis of the investigated lubricants was carried out. The forging quality was estimated on the basis of production test. The practical recommendations were given to choose an optimal oil-based colloidal-graphite lubricant for isothermal forging of Al-based alloy.

  11. Evaluation of Magnesium Die-Casting Alloys for Elevated Temperature Applications: Microstructure, Tensile Properties, and Creep Resistance

    NASA Astrophysics Data System (ADS)

    Zhu, Suming; Easton, Mark A.; Abbott, Trevor B.; Nie, Jian-Feng; Dargusch, Matthew S.; Hort, Norbert; Gibson, Mark A.

    2015-08-01

    Several families of magnesium die-casting alloys have been developed to operate at the elevated temperatures experienced in automotive powertrain applications. Most alloys are based on the Mg-Al system with alloying additions such as silicon, strontium, calcium, and rare earth elements (RE), although alloys with RE as the primary alloying constituent are also considered. This work presents an evaluation of the tensile properties and creep resistance of the most common magnesium die-casting alloys, in conjunction with the analysis of microstructure. The alloys investigated include AS31 (Mg-3Al-1Si), AJ52 (Mg-5Al-2Sr), MRI153A (Mg-9Al-1Ca-0.1Sr), MRI153M (Mg-8Al-1Ca-0.3Sr), MRI230D (Mg-6.5Al-2Ca-1Sn-0.3Sr), AXJ530 (Mg-5Al-3Ca-0.2Sr), AE42 (Mg-4Al-2RE), AE44 (Mg-4Al-4RE), and AM-HP2+ (Mg-3.5RE-0.4Zn). It is shown that, among the various alloys evaluated, MRI230D, AXJ530, and AM-HP2+ have higher yield strength than the Al alloy A380, but the ductility is relatively low at room temperature for these alloys. In contrast, AS31 and the AE series alloys have very good room temperature ductility, but their yield strength is lower than that of A380. In terms of creep resistance, MRI230D, AXJ530, AE44, and AM-HP2+ are all comparable to the Al alloy counterpart at 423 K and 448 K (150 °C and 175 °C). Microstructural factors that are most important to the strength and creep resistance of the Mg die-casting alloys are discussed.

  12. Evaluation of Surface Roughness and Tensile Strength of Base Metal Alloys Used for Crown and Bridge on Recasting (Recycling).

    PubMed

    Agrawal, Amit; Hashmi, Syed W; Rao, Yogesh; Garg, Akanksha

    2015-07-01

    Dental casting alloys play a prominent role in the restoration of the partial dentition. Casting alloys have to survive long term in the mouth and also have the combination of structure, molecules, wear resistance and biologic compatibility. According to ADA system casting alloys were divided into three groups (wt%); high noble, Noble and predominantly base metal alloys. To evaluate the mechanical properties such as tensile strength and surface roughness of the new and recast base metal (nickel-chromium) alloys. Recasting of the base metal alloys derived from sprue and button, to make it reusable has been done. A total of 200 test specimens were fabricated using specially fabricated jig of metal and divided into two groups- 100 specimens of new alloy and 100 specimens of recast alloys, which were tested for tensile strength on universal testing machine and surface roughness on surface roughness tester. Tensile strength of new alloy showed no statistically significant difference (p-value>0.05) from recast alloy whereas new alloy had statistically significant surface roughness (Maximum and Average surface roughness) difference (p-value<0.01) as compared to recast alloy. Within the limitations of the study it is concluded that the tensile strength will not be affected by recasting of nickel-chromium alloy whereas surface roughness increases markedly.

  13. Evaluation of Surface Roughness and Tensile Strength of Base Metal Alloys Used for Crown and Bridge on Recasting (Recycling)

    PubMed Central

    Hashmi, Syed W.; Rao, Yogesh; Garg, Akanksha

    2015-01-01

    Background Dental casting alloys play a prominent role in the restoration of the partial dentition. Casting alloys have to survive long term in the mouth and also have the combination of structure, molecules, wear resistance and biologic compatibility. According to ADA system casting alloys were divided into three groups (wt%); high noble, Noble and predominantly base metal alloys. Aim To evaluate the mechanical properties such as tensile strength and surface roughness of the new and recast base metal (nickel-chromium) alloys. Materials and Methods Recasting of the base metal alloys derived from sprue and button, to make it reusable has been done. A total of 200 test specimens were fabricated using specially fabricated jig of metal and divided into two groups- 100 specimens of new alloy and 100 specimens of recast alloys, which were tested for tensile strength on universal testing machine and surface roughness on surface roughness tester. Results Tensile strength of new alloy showed no statistically significant difference (p-value>0.05) from recast alloy whereas new alloy had statistically significant surface roughness (Maximum and Average surface roughness) difference (p-value<0.01) as compared to recast alloy. Conclusion Within the limitations of the study it is concluded that the tensile strength will not be affected by recasting of nickel-chromium alloy whereas surface roughness increases markedly. PMID:26393194

  14. Effect of exposure in steam or argon on the creep properties of Ni-based alloys: Creep properties of Ni-based alloys

    SciTech Connect

    Dryepondt, S.; Unocic, K. A.; Pint, B. A.

    2012-09-17

    Although expensive, Ni-based superalloys are of interest for the ultrasupercritical steam program because of their good creep and oxidation resistance at temperature above 700 C. However, the effect of steam oxidation on the alloy mechanical properties is unknown, and creep specimens of alloy CCA617, 740 and 230 were pre-oxidized for 2000 and 4000h in steam at 800 C before testing in air at the same temperature. Exposure in steam decreased the creep properties of alloy CCA617 compared with as fabricated material, had less of an effect on alloy 740, and did not affect alloy 230. Testing of a specimen repolished after steam exposure as well as microstructure observation indicate that the oxidation affected zone at the specimen surface is not responsible for the properties degradation. Surprisingly, a similar time anneal in an inert environment resulted in a drastic decrease of creep rupture life and an increase in the creep rate and elongation at rupture. TEM analysis revealed that the mechanical properties decrease for alloy CCA617 is related to the absence of precipitates in the grain.

  15. MECHANICAL BEHAVIOR OF MOLYBDENUM DISILICIDE-BASED ALLOYS

    SciTech Connect

    A. MISRA; A. SHARIF; ET AL

    2000-12-01

    We have investigated the mechanical behavior of the following single-phase polycrystalline alloys with the MoSi{sub 2} body-center tetragonal structure: MoSi{sub 2} alloyed with {approximately}2.5 at.% Re, MoSi{sub 2} alloyed with 2 at.% Al, MoSi{sub 2} alloyed with 1 at.% Nb, and MoSi{sub 2} alloyed with 1 at.% Re and 2 at.% Al. Several anomalies in the mechanical behavior of alloyed materials were observed. For example, (1) addition of only {approximately}2.5 at. % Re results in an order of magnitude increase in compressive strength at 1600 C, (2) additions of Nb and Al cause solution softening at near-ambient temperatures, and (3) quaternary MoSi{sub 2}-Re-Al alloys show strengthening at elevated temperatures and reduction in flow stress with enhanced plasticity at near-ambient temperatures in compression. The mechanisms of anomalous solution hardening and softening are discussed.

  16. Cr{sub 2}Nb-based alloy development

    SciTech Connect

    Liu, C.T.; Tortorelli, P.F.; Horton, J.A.; Easton, D.S.; Schneibel, J.H.; Heatherly, L.; Carmichael, C.A.; Howell, M.; Wright, J.L.

    1995-07-01

    Two-phase Cr-Cr{sub 2}Nb alloys (designated as CN alloys) were prepared by arc melting, followed by directional solidification, HIPping, or hot extrusion at 1450 to 1500C. The microstructure of CN alloys containing 6 to 12 at.% Nb depended strongly on alloying additions, heat treatment, and material processing. Tensile properties were sensitive to defects. Hot extrusion at 1480C was most effective in reducing as-cast defects and refining the cast Cr-Cr{sub 2}Nb eutectic structure and thus improving ductility. Beneficial alloying elements that modified the eutectic microstructure, improved oxidation resistance, or increased high-temperature strength were identified. One particular composition had a room-temperature fracture strength of 548 MPa and an ultimate tensile strength of 388 MPa, and 23% elongation at 1200C. Another CN alloy showed a fracture toughness of 7.6 MPa{radical}m at room temperature and 24.4 MPa{radical}m at 1100C. Silicide coatings applied by a pack cementation process substantially improved the oxidation resistance of the Cr-Cr{sub 2}Nb alloys at 950 and 1100C.

  17. Metallurgical structure and microhardness of four new palladium-based alloys.

    PubMed

    Vermilyea, S G; Cai, Z; Brantley, W A; Mitchell, J C

    1996-12-01

    This investigation compared the Vickers hardness and microstructures of four recently marketed, palladium-based alloys for metal-ceramic restorations. Wax patterns simulating copings for maxillary central incisors were invested in a fine-grained, carbon-free, phosphate-bonded investment. Following burnout, the palladium alloys were fused with a gas-oxygen torch, centrifugally cast, and bench-cooled. Representative castings were embedded in transparent metallographic resin and sectioned to yield two mirror-image specimens. The specimens were evaluated in either the as-cast condition or following heat treatment simulating the firing cycles for Vita VMK porcelain. Vickers hardness measurements (n = 50) were made using a 1-kg load, and photomicrographs of polished and etched specimens were obtained with a scanning electron microscope. The measured values of microhardness for the as-cast alloys were in excellent agreement with values reported by the manufacturer. The hardness in the as-cast condition was significantly greater for the Pd-Cu-Ga-In alloy, compared with the other three alloys, which did not contain copper. For the three high-palladium (> or = 75 wt%) alloys, there were small (4%-8%) decreases in hardness following heat treatment, whereas a larger decrease (13%) in hardness occurred for the Pd-Ag-In-Sn alloy after heat treatment. The porcelain firing cycles caused microstructural homogenization for all four alloys, and the relatively thick near-surface oxidation region in the Pd-Cu-Ga-In and Pd-Ag-In-Sn alloys was not observed in the two heat-treated Pd-Ga-Ag-In-Au alloys. The multiphasic microstructures of these alloys may have some significance for the in vitro and clinical corrosion behavior and the metal-ceramic bond strength. The hardness for the three high-palladium alloys may be controlled by submicroscopic precipitates that remain unaltered by heat treatment. The significantly greater hardness for the Pd-Cu-Ga-In alloy may cause greater difficulty

  18. Noncontact atomic force microscopy imaging of atomic structure and cation defects of the polar MgAl2O4 (100) surface: Experiments and first-principles simulations

    NASA Astrophysics Data System (ADS)

    Rasmussen, Morten K.; Foster, Adam S.; Canova, Filippo F.; Hinnemann, Berit; Helveg, Stig; Meinander, Kristoffer; Besenbacher, Flemming; Lauritsen, Jeppe V.

    2011-12-01

    Atom-resolved noncontact atomic force microscopy (NC-AFM) was recently used to reveal that the insulating spinel MgAl2O4(100) surface, when prepared under vacuum conditions, adopts a structurally well-defined Al and O-rich structure (Al4-O4-Al4 termination) consisting of alternating Al and double-O rows, which are, however, interrupted by defects identified as interchanged Mg in the surface layers (so-called antisite defects). From an interplay of futher NC-AFM experiments and first-principles NC-AFM image simulations, we present here a detailed analysis of the NC-AFM contrast on the MgAl2O4(100) surface. Experiments show that the contrast on MgAl2O4(100) in atom-resolved NC-AFM is dominated by two distinctly different types of contrast modes, reflecting two oppositely charged tip-apex terminations. In this paper, we analyze the contrast associated with these imaging modes and show that a positively charged tip-apex (presumably Mg2+) interacts most strongly with the oxygen atoms, thus imaging the oxygen lattice, whereas a negatively charged tip-apex (O2-) will reveal the cation sublattice on MgAl2O4. The analysis of force-vs-distance calculations for the two tips shows that this qualitative picture, developed in our previous study, holds for all realistic tip-surface imaging parameters, but the detailed resolution on the O double rows and Al rows changes as a function of tip-surface distance, which is also observed experimentally. We also provide an analysis of the tip dependency and tip-surface distance dependency for the NC-AFM contrast associated with single Al vacancies and Mg-Al antisite defects on the MgAl2O4(100) surface and show that it is possible on the basis of NC-AFM image simulations to discriminate between the Al3+ and Mg2+ species in antisite defects and hypothetical Al vacancies.

  19. Ignition characteristics of the nickel-based alloy UNS N07718 in pressurized oxygen

    NASA Technical Reports Server (NTRS)

    Bransford, James W.; Billiard, Phillip A.; Hurley, James A.; Mcdermott, Kathleen M.; Vazquez, Isaura

    1989-01-01

    The development of ignition and combustion in pressurized oxygen atmospheres was studied for the nickel based alloy UNS N07718. Ignition of the alloy was achieved by heating the top. It was found that the alloy would autoheat to destruction from temperatures below the solidus temperature. In addition, endothermic events occurred as the alloy was heated, many at reproducible temperatures. Many endothermic events occurred prior to abrupt increases in surface temperature and appeared to accelerate the rate of increase in specimen temperature. It appeared that the source of some endotherms may increase the oxidation rate of the alloy. Ignition parameters are defined and the temperatures at which these parameters occur are given for the oxygen pressure range of 1.72 to 13.8 MPa (250 to 2000 psia).

  20. Perfect cubic texture, structure, and mechanical properties of nonmagnetic copper-based alloy ribbon substrates

    NASA Astrophysics Data System (ADS)

    Khlebnikova, Yu. V.; Rodionov, D. P.; Gervas'eva, I. V.; Egorova, L. Yu.; Suaridze, T. R.

    2015-03-01

    A sharp cubic texture is formed in a number of copper alloys subjected to cold deformation by rolling by 98.6-99% followed by recrystallization annealing, which opens up fresh opportunities for long thin ribbons made of these alloys to be used as substrates in the production of second-generation high- T c superconductor (2G HTSC) cables. The possibility of creating ternary alloys based on a binary Cu-30 at % Ni alloy with additional elements that harden its fcc matrix (iron, chromium) is shown. The measurements of the mechanical properties of textured ribbons made of these alloys demonstrate that their yield strength is higher than that of a textured ribbon made of pure copper by a factor of 2.5-4.5.