To see the other types of publications on this topic, follow the link: Mg2Si.
Dissertations / Theses on the topic 'Mg2Si'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 46 dissertations / theses for your research on the topic 'Mg2Si.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Esch, David J. N. "Transverse Thermoelectric Properties of Cu/Mg2Si and Ni/Mg2Si Artificially Anisotropic Materials." ScholarWorks@UNO, 2015. http://scholarworks.uno.edu/td/1967.
Full textAbstract:
In this thesis the spark plasma sintering process (SPS) was used to press Mg2Si powder with Ni and Cu slices into alternating layer stacks. These stacks, once cut at an angle, are an artificially anisotropic material. This anisotropy provides transverse thermoelectric properties to the sample. The transverse transport properties were measured along with the individual component transport properties. The SPS process provided malleable samples that gave a power factors of for the Ni/Mg2Si stack and for the Cu/Mg2Si stack. These fall short of the theoretical calculations which would give the power factors as .0254 for the Ni/Mg2Si stack and .211 for the Cu/Mg2Si stack. It is theorized that eddy currents and interface resistances between the layers are the causes for these discrepancies.
2
Le, Quoc Huy. "Matériaux thermoélectriques du type Mg2Si-Mg2Sn élaborés en couches minces par co-pulvérisation assistée par plasma." Thesis, Grenoble, 2011. http://www.theses.fr/2011GRENY072/document.
Full textAbstract:
Cette thèse présente une étude de l'élaboration et des propriétés structurales, ainsi que des propriétés électriques, des couches minces de matériaux thermoélectriques de type Mg2Si-Mg2Sn. Les couches minces polycristallines du composé Mg2Sn et des solutions solides Mg2Si1-xSnx ont été réalisées sur plusieurs types de substrat, à température ambiante, par la technique de dépôt par co-pulvérisation assistée par plasma micro-onde multi-dipolaire. L'influence des paramètres de dépôt sur les propriétés structurales et électriques des couches élaborées a été étudiée. Ainsi, la composition chimique des couches a été parfaitement contrôlée par le biais de la polarisation indépendante des cibles des éléments constituants. La composition de phase, ainsi que la microstructure des couches, ont été trouvées dépendant de la pression de dépôt, de la distance entre des cibles et le substrat, de la puissance micro-onde et de la configuration du réacteur de dépôt. Ces propriétés structurales, à leur tour, ont un fort impact sur les propriétés électriques des couches déposées. Les couches minces Mg2Sn dopé en Ag, déposées avec la condition de dépôt optimale, ont présenté un facteur de puissance à température ambiante comparable à celui des matériaux actuellement utilisés. Les couches minces des solutions solides Mg2Si1-xSnx présentent, pourtant, des facteurs de puissance encore modestes résultant notamment des faibles conductivités électriquesThis thesis presents a study of the deposition and structural as well as electrical properties of thin films of thermoelectric materials Mg2Sn-Mg2Si. Polycrystalline thin films of the Mg2Sn compound and solid solutions Mg2Si1-xSnx were deposited on several types of substrate at room temperature, by co-sputtering assisted by microwave plasma. The influence of deposition parameters on structural and electrical properties of deposited films was studied. Thus, the chemical composition of layers was fully controlled by the means of the independent polarization of target of constituent elements. Phase composition and microstructure of deposited films were found depending on the deposition pressure, on the distance between targets and the substrate, on the microwave power, as well as on the configuration of the deposition reactor. These structural properties, in turn, have a strong impact on the electrical properties of the deposited films. Mg2Sn thin films doped with Ag, deposited under optimal condition, presented a power factor at room temperature comparable to conventional thermoelectric materials. Thin films of solid solutions Mg2Si1-xSnx present, however, power factors still modest due in particular to low electrical conductivities
3
Le-Quoc, Huy. "Matériaux thermoélectriques du type Mg2Si−Mg2Sn élaborés en couches minces par co-pulvérisation assistée par plasma." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00687307.
Full textAbstract:
Les travaux présentés dans cette thèse portent sur l'élaboration des couches minces de matériaux thermoélectriques de type Mg2Si-Mg2Sn, et sur l'étude de leurs propriétés structurales et électriques. Des couches minces polycristallines du composé Mg2Sn et des solutions solides Mg2Si1-xSnx ont été réalisées sur plusieurs types de substrat, à température ambiante, par la technique de dépôt par co-pulvérisation assistée par plasma micro-onde multi-dipolaire. L'influence des paramètres de dépôt sur les propriétés structurales et électriques des couches élaborées a été étudiée. Les résultats obtenus démontrent clairement que la composition chimique des couches est parfaitement contrôlée par le biais de la polarisation indépendante des cibles des éléments constituants. Cette étude met également en évidence que la composition de phase et la microstructure des couches dépendent des paramètres opératoires : pression du gaz plasmagène, puissance micro-onde, géométrie (distance cibles-substrat, configuration du réacteur de dépôt). Les propriétés structurales ont un fort impact sur les propriétés électriques des couches déposées. Un facteur de puissance comparable, à température ambiante, à celui des matériaux actuels (Bi-Te) a été déterminé pour les couches minces Mg2Sn dopées en Ag. Une grande avancée de cette étude a été de prouver l'obtention des couches minces des solutions solides Mg2Si1- xSnx monophasées. Des améliorations sont proposées pour l'augmentation de la conductivité électrique et donc du facteur de puissance de ces couches.
4
Le, quoc Huy. "Matériaux thermoélectriques du type Mg2Si-Mg2Sn élaborés en couches minces par co-pulvérisation assistée par plasma." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00859213.
Full textAbstract:
Cette thèse présente une étude de l'élaboration et des propriétés structurales, ainsi que des propriétés électriques, des couches minces de matériaux thermoélectriques de type Mg2Si-Mg2Sn. Les couches minces polycristallines du composé Mg2Sn et des solutions solides Mg2Si1-xSnx ont été réalisées sur plusieurs types de substrat, à température ambiante, par la technique de dépôt par co-pulvérisation assistée par plasma micro-onde multi-dipolaire. L'influence des paramètres de dépôt sur les propriétés structurales et électriques des couches élaborées a été étudiée. Ainsi, la composition chimique des couches a été parfaitement contrôlée par le biais de la polarisation indépendante des cibles des éléments constituants. La composition de phase, ainsi que la microstructure des couches, ont été trouvées dépendant de la pression de dépôt, de la distance entre des cibles et le substrat, de la puissance micro-onde et de la configuration du réacteur de dépôt. Ces propriétés structurales, à leur tour, ont un fort impact sur les propriétés électriques des couches déposées. Les couches minces Mg2Sn dopé en Ag, déposées avec la condition de dépôt optimale, ont présenté un facteur de puissance à température ambiante comparable à celui des matériaux actuellement utilisés. Les couches minces des solutions solides Mg2Si1-xSnx présentent, pourtant, des facteurs de puissance encore modestes résultant notamment des faibles conductivités électriques.
5
Balout, Hilal. "Thermoelectric properties of Mg2Si-based systems investigated by combined DFT and Boltzmann theories." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4301.
Full textAbstract:
Les propriétés électroniques et thermoélectriques de matériaux basés sur Mg2Si ont été étudiées par calculs DFT et semi-classiques (théorie de Boltzmann). Les effets d’abaissement de dimensionalité et de contraintes ont été étudiés. Les calculs ont été effectués sur les films monocristallins orientés 001, 110 et 111 et sur les films polycristallins. Seul le film monocristallin orienté 110 a montré des propriétés thermoélectriques intéressantes. Trois types de contraintes ont été investiguées: uniaxiale, biaxiale et isotrope. L’augmentation de la contrainte sur Mg2Si produit un décalage du maximum du facteur de puissance (PF) vers les basses températures. Comparé à Mg2Si non contraint, le coefficient Seebeck (S) augmente uniquement sous contrainte isotrope. On montre l’équivalence des propriétés thermoélectriques entre Mg2Si contraint dans la direction [110] et celles du film orienté 110. Les contraintes de tension isotropes ont été modélisées en insérant des atomes Sb dans Mg2Si massif conduisant aux structures Mg2Si:Sb, Mg2Si:3Sb and Mg2Si:4Sb. Seul Mg2Si:4Sb produit une contrainte isotrope. Les effets de substitutions de Sn pour Si dans Mg2Si massif sont similaires à ceux observés pour Mg2Si sujet à des contraintes en tension uniaxiales et biaxiales. Pour les films Mg2Si1−xSnx orientés 110 le S du matériau dopé p est supérieur à celui des massifs Mg2Si et Mg2Si1−xSnx. Concernant les nanostructures, le super-réseau Mg2Si/Mg2Sn est le plus intéressant lorsque faiblement dopé p et à basse température. Les assemblages de fils sont les meilleurs en tant que matériaux faiblement dopés n et à basse température: le PF est quasiment doublé par rapport à celui de Mg2Si massifThe electronic and thermoelectric properties of Mg2Si-based materials have been investigated by means of DFT calculations and semi-classical Boltzmann theory. The low-dimensional and strain effects on these properties have been studied. The properties have been investigated on 001-, 110- and 111-oriented Mg2Si monocrystalline films, and on polycrystalline Mg2Si film. Only the 110-oriented monocrystalline film has been found to have interesting thermoelectric properties. Three types of strains have been investigated: uniaxial, biaxial and isotropic. Increasing the intensity of the strain on Mg2Si induces a shift of the power factor (PF) maximum towards low temperature. Compared with unstrained Mg2Si, the Seebeck coefficient (S) increases only under isotropic strain. We evidence an equivalence in the thermoelectric properties between Mg2Si material constrained in the [110] direction and the 110-oriented Mg2Si film. Isotropic tensile strains have been modeled by inserting Sb atoms in bulk Mg2Si leading to the stuctures Mg2Si:Sb, Mg2Si:3Sb and Mg2Si:4Sb. Only Mg2Si:4Sb is found to induces such type of constraints. The effects of the Sn for Si substitutions in bulk Mg2Si are very similar to those observed for Mg2Si subjected to uniaxial and biaxial tensile strains. For (110)-oriented Mg2Si1−xSnx films S of the n−doped material outperforms that of the bulk Mg2Si and bulk Mg2Si1−xSnx. Regarding nanostructures, the Mg2Si/Mg2Sn superlattice is most interesting as a p-doped material at low carrier concentration/low temperature. The stick assemblage is best as a n-doping material at low carrier concentration/low temperature where its PF is almost twice as high as that of bulk Mg2Si
6
Uyma, Falko. "Untersuchungen auf dem Gebiet der Al-Mg-Si- und Al/Mg2Si-in-situ Legierungen." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2009. http://nbn-resolving.de/urn:nbn:de:bsz:105-366350.
Full textAbstract:
Das Ziel dieser Arbeit bestand in der Entwicklung eines Werkstoffes auf Basis der Legierung AlSi13,5Mg9,5 (=Al-15Mg2Si-8Si), die sich durch ein verbessertes Verschleißverhalten, geringere thermische Ausdehnung und geringere Dichtewerte auszeichnet. Eine wesentliche Aufgabe der Arbeit bestand in der Einstellung bester mechanischer Eigenschaften durch die Feinung der Primär-Phase (Mg2Si) sowie durch Mikrolegieren. Ausbleibende Resultate begründeten die Wahl einer angepassten Legierungszusammensetzung AlMg8,6Si6,4 (=Al-14Mg2Si-1Si). Versuche zur Eigenschaftsoptimierung (Mikrolegieren, Wärmebehandlung) zeigten neben der Ermittlung der gießtechnischen Eigenschaften die spezifischen Legierungscharakteristika auf. Die Verarbeitung des optimierten Werkstoffes mit verschiedenen Verfahren machte die Abhängigkeit der Ausbildung der mechanischen Eigenschaften sowie des Gefüges deutlich. Die Untersuchung der thermo-physikalischen Eigenschaften sowie die Analyse der Wechselwirkungen zwischen Risswachstum und Gefüge runden die Beschreibung des Eigenschaftsprofiles ab.
7
Ellendt, Nils [Verfasser]. "Einfluss der Prozessparameter auf Porosität und Mikrostruktur sprühkompaktierter übereutektischer Al-Mg2Si-Legierungen / Nils Ellendt." Aachen : Shaker, 2010. http://d-nb.info/108188598X/34.
Full text
8
Yan, Feng. "Development of high strength Al-Mg2Si-Mg based alloy for high pressure diecasting process." Thesis, Brunel University, 2014. http://bura.brunel.ac.uk/handle/2438/13883.
Full textAbstract:
Aluminium alloys are the most promising lightweight materials used in the automotive industry to achieve weight reduction for improving fuel efficiency and reducing CO2 emissions. High pressure diecasting (HPDC) is a fast and economical near-net shape manufacturing method to produce engineering components. About 80% of cast aluminium alloys are currently manufactured by HPDC. The increased demands of manufacturing structural components by HPDC process require high strength Al-alloys for the automotive industry. However, the currently available die cast Al-alloys are unable to fulfil this requirement. Al-Mg2Si alloy is known as an alloy capable of providing superior high strength by Mg2Si particles. However, Al-Mg2Si alloy is not applicable in the HPDC process because of the severe die soldering problem. This has limited its applications throughout industries. Moreover, the existing studies on the Al-Mg2Si alloy are mainly focused on the hyper-eutectic alloys and limited information is available for hypo-eutectic alloys. Generally, the mechanical properties of Al-alloys are determined by the alloy composition, the defect levels in the components, the microstructure which is mainly controlled by the casting process and heat treatment process. Due to the high cooling rate provided by the die block in the HPDC process, the refined microstructure in the die cast Al-Mg2Si alloys can be obtained to improve the mechanical properties. Therefore, the development of high strength Al-Mg2Si based alloys for the HPDC process is significant for manufacturing quality automotive components. The present study mainly focuses on the alloy development for the HPDC process. In order to make die castable Al-Mg2Si based alloys, the effect of excess Mg has been investigated to modify the hypo-eutectic Al-Mg2Si system for improving the mechanical properties. The effect of excess Mg on the solidification and microstructural evolution, and the mechanical properties of Al-Mg2Si alloys, has also been investigated by the combination of thermodynamic calculation and the experimental validation. The excess Mg in the hypo-eutectic Al-Mg2Si alloys has been found to be able to shift the eutectic composition to a lower Mg2Si content, which means that the hypo-eutectic composition of Al-Mg2Si alloy can be at eutectic or hyper-eutectic compositions after adding different levels of excess Mg. The experimental trials have also found that Al-8Mg2Si-6Mg alloy provides the best combination of strength and ductility in the as-cast castings made by the HPDC process. This can be further enhanced by adding 0.6wt.% Mn, which exhibits yield strength of 189MPa, UTS of 350MPa, and elongation of 6.5%. Investigations have also revealed that the Al-8Mg2Si-6Mg alloy exhibits a relatively high tolerance to the Fe impurity because of the insignificant reduction of ductility of the alloy. The elongation is still at a level of 5% when Fe is at 1.6wt.% in the alloy. Furthermore, Cu and Zn can further enhance the mechanical properties of the Al-8Mg2Si-6Mg-0.6Mn alloy. Cu contents between 0.31wt.% and 0.92wt.% in the Al-8Mg2Si-6Mg-0.6Mn alloy can increase the yield strength from 193MPa to 207MPa, but decrease the UTS from 343MPa to 311MPa, and the elongation from 4.8% to 3.8% under as-cast condition. This can be attributed to the formation of hot tearing defects in castings. Therefore, the Cu content in the alloy should be limited to a low level. On the other hand, zinc can be controlled to a level of 4.3wt.%, which will dramatically increase the tensile strength of the alloy. More importantly, Zn can significantly increase the mechanical properties of the alloy after a quick T6 heat treatment under a condition of solution at 490oC for 15 mins and ageing at 180oC for 90 mins, at which the yield strength is 345MPa, UTS is 425MPa, and elongation is 3.2 %. In the present study, the solidification and microstructural evolution, the relationship between the microstructure and mechanical properties, and the strengthening mechanisms in the developed alloy are discussed on the basis of the experimental results. A two stage solidification has been recognised to be responsible for the microstructure formation in the HPDC process. The primary α-Al phase is formed as prior phase for the hypo-eutectic alloy and the primary Mg2Si phase is formed as prior phase for the hyper-eutectic alloy. The solute elements including Mg, Mn, Fe, Cu, and Zn can enhance the solution strengthening and/or the precipitation strengthening in the alloys, but alter the solidification ranges, which will affect the formation of defects in the castings. In the quick T6 heat treatment, the AlMgZn phase is dissolved into the Al phase during solution treatment and precipitated during ageing treatment. The quick heat treatment is also found to be able to spheroidise the Mg2Si phase. Only η′ MgZn phase is precipitated during aging in Zn containing alloys. The alloy with 4.3wt.% Zn provides the best combination of the mechanical properties because of the high density of MgZn precipitates in the α-Al phase.
9
Dedov, Stanislav. "Untersuchungen zur Entwicklung einer kombinierten Gieß-Umformtechnologie zur Herstellung hochwertiger Aluminium Bauteile." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2013. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-128707.
Full textAbstract:
Die steigende Bedeutung des Leichtbaus in der modernen Fahrzeugtechnik stellt stetig neue technologische Herausforderungen an die Hersteller. Dabei rückt die Entwicklung neuer energetisch effizienter Herstellungsverfahren sowie geeigneter Werkstoffe immer weiter in den Vordergrund. In der vorliegenden Arbeit wird die Entwicklung eines zukunftsorientierten kombinierten Gieß-Umformverfahrens zur Herstellung hochfester Aluminiumbauteile, z.B. für die Automobilindustrie, vorangetrieben. Die Anwendung aushärtbarer Aluminiumlegierungen, insbesondere mit höheren Siliziumgehalten, wird betrachtet. Der Schwerpunkt der Arbeit liegt in der Ermittlung und Begründung günstiger Prozessbedingungen für einzelne Prozessschritte von Aluminiumbauteilen (Gießen, Umformen, Warm-, bzw. Kaltauslagern) im Zusammenhang mit dem Siliziumgehalt der Legierung. Die Übertragung der gewonnenen Erkenntnisse auf die Verhältnisse des kombinierten Gieß-Umformverfahrens in einen industrienahen Maß-stab stellte ein weiteres Ziel der Arbeit dar.
10
Contatori, Chester. "Efeitos do cobre e do magnésio na microestrutura da liga Al-19%Si fundida por centrifugação." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-29012018-143638/.
Full textAbstract:
As ligas de alumínio hipereutéticas fundidas por centrifugação apresentam a possibilidade de obtenção de um gradiente funcional de propriedades no material (Functionally Graded Material - FGM). Na fundição por centrifugação, os compostos menos densos tenderão a se concentrar no diâmetro interno de um tubo centrifugado. Como a massa específica do silício e do Mg2Si são menores do que a do alumínio, as partículas dessas fases tendem a concentrar-se na parede interna de tubos centrifugados. Em função disto, este estudo tem como objetivo dar uma contribuição ao entendimento dos mecanismos de migração das partículas de silício e de Mg2Si numa liga de alumínio hipereutética com 19% de silício e com adições de cobre e magnésio fundidas por centrifugação. Diante disto, foram obtidos tubos da liga Al-19%Si com adições de até 5% de cobre e 5% de magnésio por meio da fundição centrífuga numa rotação de 1700 rpm. A caracterização microestrutural em diversas regiões dos tubos centrifugados foi feita utilizando-se a microscopia óptica e eletrônica de varredura com sistema de análise de imagens. A fração das fases presentes e a dureza Vickers foram determinadas ao longo da parede do tubo em diversas posições de vazamento. A fundição centrífuga promove a segregação de partículas de silício primário e de Mg2Si, com massas específicas menores para a parede interna do tubo. Esta segregação é mais acentuada na região final de vazamento devido ao maior tempo de centrifugação até a solidificação. Uma retenção de partículas junto à parede externa do tubo ocorre em decorrência da mais elevada taxa de resfriamento da liga fundida em contato com a parede do molde mais frio. Esta retenção também foi maior na região do tubo de início de vazamento em relação à de final de vazamento. A adição de cobre intensificou a migração das partículas devido ao aumento da densidade do líquido. O aumento do teor de cobre na liga também inibiu a presença de dendritas de alumínio primário que ocorrem em grandes quantidades nas regiões centrais das paredes dos tubos centrifugados. O perfil de dureza ao longo da parede do tubo indicou um aumento de dureza relacionado diretamente à quantidade de partículas de silício (β) e Mg2Si.A functionally gradient material, in terms of its properties, can be obtained with centrifugally cast hypereutectic aluminum alloys. In centrifugal casting, the less dense compounds tend to concentrate close to the inner wall of a centrifugally cast tube. Since the specific mass of silicon and Mg2Si are less than that of aluminum, particles of these phases tend to concentrate at the inner walls of centrifugally cast tubes. On the basis of this, the aim of this study was to contribute towards increased understanding of the mechanism of segregation of silicon and Mg2Si particles in a centrifugally cast hypereutectic aluminum - 19% silicon alloy to which copper and magnesium were added. Hence, tubes of Al-19%Si alloy with up to 5% copper and up to 5% magnesium were centrifugally cast at rotational speed of 1700 rpm. Microstructural examination of various regions of the centrifugally cast tubes was carried out using an optical microscope and a scanning electron microscope coupled to an image analyzer. The amount of phases that formed and the Vickers hardness were determined across the thickness of the tube at different positions. Centrifugal casting promotes segregation of primary silicon and Mg2Si particles, (with lower specific weights) towards the inner walls of the tube. This segregation was higher at regions that were last to be cast, and due to longer centrifugation until solidification. Retention of particles close to the outer wall of the tube took place due to higher cooling rate of the cast alloy in contact with the cold walls of the mold. This retention was also higher at regions of the tube that were cast first compared with those that were cast last. The addition of copper increased particle migration due to increase in density of the liquid. Increase in the amount of copper in the alloy also inhibited the presence of primary aluminum dendrites that form in large quantities at the central regions of centrifugally cast tube walls. The hardness profile along the tube wall indicated an increase in hardness and this is directly related to the quantity of (β) silicon and Mg2Si particles.
11
Chassagnon, Rémy. "Apports des simulations HREM et ELNES à la caractérisation interfaciale : cas de l'interface corindon/Mg2Si produite à l'état solide." Lyon, INSA, 2000. http://www.theses.fr/2000ISAL0103.
Full textAbstract:
L'étude que nous présentons s'inscrit dans un contexte de matériaux composites où les propriétés intéressantes résultent de l'insertion de particules céramiques monocristallines d' Al203-α dans un alliage à base aluminium Al(Mg, Si) susceptible de développer un processus de durcissement structural. Cependant, les régions interfaciales (alliage au contact des particules) sont le siège d'une évolution thermodynamique différente de celle présente au sein de l'alliage. Le renfort céramique se revêt de cristaux de Mg2Si sous sa forme thermodynamique stable. L'adhésion de ce composé est capitale pour la tenue mécanique du composite ; son approche a été menée par une caractérisation cristallo-chimique locale de l'interface précipité/renfort. A l'aide d'un microscope électronique à émission de champ, deux techniques à haute résolution spatiale ont été mises en œuvre : l'imagerie par microscopie électronique en transmission à haute résolution (METHR) et l'analyse chimique locale par spectroscopie de pertes d'énergie des électrons (EELS). En METHR, l'analyse par comparaison des images expérimentales et des images simulées, produites par plusieurs modèles atomiques de l'interface, a mis en évidence la présence des espèces 0 et Si à l'interface. En ce qui concerne la seconde approche, nous avons précisé les signatures ELNES des atomes Al, Mg, Si dans différents environnements tant par des acquisitions expérimentales que par des simulations de spectres de pertes de plusieurs matériaux (aluminium, alumine, siliciure de magnésium). Ces simulations ELNES ont été conduites avec le support de programmes de chimie quantique pour le calcul des potentiels auto-cohérents et de programmes de diffusion multiple (ICXANES) utilisés par la communauté des physiciens de la spectroscopie X. Les résultats. Issus de l'acquisition des signatures en mode nanosonde, vont dans le sens du modèle retenu par METHRThe study that we present fits in with a composite materials context where the interesting properties result from the monocristalline Al203-α ceramic particles insertion in aluminium based alloy Al(Mg, Si) able to develop a structural hardening process. However, the interfacial area (alloy in contact with the particles) is the seat of a thermodynamic evolution different from that in the bulk. The ceramic reinforcement is covered with Mg2Si precipitates in their stable thermodynamic phase. The adhesion of this compound is capital for the mechanical behaviour of the composite; its approach was carried out by a local cristallo-chemical characterization of the interface precipitate/reinforcement. Using a field emission electron microscope, two high spatial resolution techniques were implemented: the high resolution transmission electron microscopy imaging (HREM) and the local chemical analysis by electron energy loss spectroscopy (EELS). In HREM approach, the comparison between the experimental images and the simulated images, produced by several atomic models of the interface, highlighted the presence of the 0 and Si species at the interface. With regard to the second approach, we produced ELNES signatures of the Al, Mg, Si atoms in various environments as well by experimental acquisitions as by simulations of energy loss spectra of several Materials (aluminum, alumina, magnesium silicide). These ELNES simulations were led with the support of quantum chemistry codes for the calculation of the self-coherent potentials and of multiple scattering codes (ICXANES) used by the community of the physicists of the X spectroscopy. The results, obtained from the acquisition of the signatures in nanosonde mode, go in the direction of the model retained by HREM
12
Baranek, Philippe. "Approche ab initio des propriétés dynamiques en milieu cristallin : constantes élastiques et phonons Mg2Si, transitions de phase dans KNbO3." Lille 1, 1998. https://pepite-depot.univ-lille.fr/LIBRE/Th_Num/1998/50376-1998-175.pdf.
Full textAbstract:
Maitriser les mecanismes de transition de phase qui menent a la ferroelectricite est un objectif essentiel dans la domaine des materiaux laser dans la mesure ou les proprietes optiques de ces materiaux dependent fortement de la symetrie de la phase de la matrice cristalline hote. Les calculs ab initio peuvent apporter des elements utiles du point de vue de la comprehension de ces phenomenes. Dans ce contexte, ce travail propose une etude en deux parties. La premiere partie vise a tester deux methodes ab initio : le modele hartree-fock et la theorie de la fonctionnelle de la densite (dft) en les appliquant au calcul des proprietes structurales, dynamiques et elastiques du semiconducteur mg#2si. La comparaison des resultats permet de discuter les avantages et inconvenients de ces modeles, notamment concernant la prise en compte de la correlation. La seconde partie est consacree a la structure electronique et aux transitions entre les quatre phases experimentalement connues de la matrice cristalline knbo#3. Leur stabilite relative a ete analysee grace a la determination de l'hypersurface de potentiel electronique dans la direction des modes mous au point et des relaxations des atomes du modele a huit sites. Une attention particuliere a ete portee a l'evolution des proprietes dynamiques lors des transitions de phase.
13
Prahoveanu, Codrin. "Mg2Si, Mg2(Si,Sn) et barrières de diffusion déposées en couches minces par co-pulvérisation assistée par plasma micro-onde pour des applications thermoélectriques pour l'automobile." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI091/document.
Full textAbstract:
Cette thèse concerne le dépôt de couches minces par la méthode de co-pulvérisation assistée par plasma micro-onde dans le contexte de leurs applications potentielles pour la thermoélectricité. Deux volets principaux ont été développés au cours de ce travail: la synthèse et l'étude des propriétés de couches minces à base de Mg2Si et Mg2(Si,Sn) pour une mise en œuvre au sein de modules thermoélectriques miniaturisés, et l'étude de matériaux susceptibles d’agir comme barrières de diffusion entre un thermoélément à base de Mg2Si et les joints de brasage utilisés pour connecter les contacts électriques. Dans la première partie de l'ouvrage, des couches minces de solutions solides de Mg2(Si,Sn), avec une stœchiométrie proche de Mg2Si0.4Sn0.6, ont été déposées sur différents substrats. Les propriétés thermomécaniques de ces couches ont été étudiées en fonction du processus de dépôt et de la nature du substrat, tandis que la stabilité thermique et la réactivité avec les substrats ont été examinées, ont fonction de la composition, dans le domaine de températures intermédiaires. En outre, les propriétés de transport des couches minces de Mg2Si dopé au Sb ont été caractérisées, en s’intéressant, en particulier, à l’effet de la texturation de la couche mince sur les propriétés thermoélectriques (coefficient Seebeck, conductivité électrique et thermique). La deuxième partie de cette thèse est dédiée au dépôt de couches barrières sur des échantillons massifs de Mg2(Si,Ge) dopés Bi afin de limiter la diffusion et la réactivité entre le thermoélément et le joint de brasage à base d'alliage Al-Si dans le but d’obtenir un contact électrique chimiquement stable et de faible résistance. Deux options ont été étudiées : l'une est basée sur des couches à gradient destinées à ajuster progressivement la composition entre celle du thermoélément et une couche supérieure de Ni qui constitue la barrière de diffusion. L'autre option concerne les bi-couches M/Ni, où M est un métal (Ti, Ta, W ou Cr). Globalement, le travail présenté ici offre un aperçu du potentiel des couches minces à base de Mg2Si et Mg2(Si,Sn) dans la réalisation d'un module thermoélectrique miniaturisé et l'étude de faisabilité de différents matériaux comme barrières de diffusion dans des modules conventionnelsIn this thesis are presented the deposition of thin films by microwave plasma-assisted cosputtering and their characterization within the context of thermoelectric applications. The aims of the work are split into two categories: the investigation of Mg2Si and Mg2(Si,Sn) thin films in terms of their potential to be implemented in a miniaturized thermoelectric module and the inquiry of materials which may act as diffusion barriers at the interface between Mg2Si-based thermoelements and the brazing joints used in the preparation of electrical contacts. In the first part of the work, thin films of Mg2(Si,Sn) solid solutions with a stoichiometry close to Mg2Si0.4Sn0.6 have been deposited on various substrates. The thermomechanical properties of these films have been investigated with respect to their dependence on the deposition process and the nature of the substrate on which they are grown, while the thermal stability and reactivity with the substrates at intermediate temperatures based on their composition has been explored. Furthermore, the transport properties of Sb-doped Mg2Si thin films have been also characterized. This was done in the context of finding the evolution and dependence of the thermoelectric properties (Seebeck coefficient, electrical and thermal conductivities) to the level of texturing within the thin film. The second part of this thesis involves the deposition of diffusion barriers on bulk Bi-doped Mg2(Si,Ge) thermoelements in order to disrupt the diffusion and reactivity between the thermoelectric leg and the Al-Si alloy-based brazing joint and to obtain a chemically stable, low resistive electrical contact. With this objective, two options have been pursued. One is based on the deposition of gradient layers that are meant to gradually inverse the composition from the Mg2(Si,Ge) thermoelements to a top layer of Ni that is used in the deposition of the potential diffusion barrier. The other option concerns the deposition of a M/Ni bilayer on the TE legs, where M is a metallic layer (Ti, Ta, W or Cr). Overall, the work presented here offers a glimpse of the potential use of Mg2Si and Mg2(Si,Sn) thin films in the making of a miniaturized thermoelectric module and the efficiency of various materials as diffusion barriers in the industry of thermoeletrics
14
Reinfried, Nikolaus. "Modifizierung der Werkstoffe auf Basis von Magnesiumsilicid mit Hilfe der Spark-Plasma-Synthese." Doctoral thesis, [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=983915865.
Full text
15
Reinfried, Nikolaus. "Modifizierung der Werkstoffe auf Basis von Magnesiumsilicid mit Hilfe der Spark-Plasma-Synthese." Doctoral thesis, Technische Universität Dresden, 2006. https://tud.qucosa.de/id/qucosa%3A24816.
Full textAbstract:
Die umfangreichen Untersuchungen ausgewählter Mg2Si-basierter Materialien innerhalb dieser Arbeit zeigen neue Wege für die Anwendung der SPS-Technik in der Grundlagen- als auch angewandten Forschung und liefern entscheidendes, neues Material für die Charakterisierung der Li-Verbindungen Li2xMg2-xX (X = Si, Ge, Sn, Pb). Aufbauend auf vorangegangenen Arbeiten und den hier dargestellten Resultaten ergeben sich sowohl neue Möglichkeiten der Synthese, basierend auf dem SPS-Prozess (in Verbindung mit der Pulverherstellung, ‑verarbeitung und einem entsprechenden Werkzeugdesign), als auch eine Optimierung der Materialeigenschaften von Verbundwerkstoffen durch Nutzung dieser Technik. Die ternären Phasen Mg2Si1−xXx (X = Ge, Sn, Pb) und Mg2−x/2Si1−xSbx Die pulvermetallurgische Herstellung der Phasen Mg2Si1-xXx (X = Ge, Sn und Pb) und der Phase Mg2‑x/2Si1-xSbx gelang in dieser Arbeit erstmals mit Hilfe der SPS-Technik aus kugelgemahlenen Pulvergemischen (MgH2, Si, X). Die ternären Phasen Li2xMg2−xX (X = Si, Ge, Sn, Pb) Der Einbau von Li in Mg2Si wurde in dieser Arbeit erstmalig durch die SPS-Festkörperreaktion aus LiH, MgH2 und Si untersucht. Die Synthese der Li-armen Li2xMg2−xSi-Phasen gelingt schon bei Temperaturen von max. 700 °C. Die Schmelzsynthese dieser extrem luft- und feuchtigkeitsempfindlichen Proben wurde unter Argon-Schutzgas aus den Elementen mit anschließender Wärmebehandlung bei 200 °C angewendet. Dabei lassen sich drei unterschiedliche kubische Li2xMg2−xSi-Phasen mit 0 < x < 0,8 auf der Mg2Si-reichen Seite des ternären Systems finden. Mit steigendem Li-Gehalt können röntgenographisch zwei strukturelle Umwandlungen, ausgehend von der Raumgruppe Fm-3m für Mg2Si zu P-43m und P-43m mit der Bildung einer Überstruktur mit a′ = 2a bestimmt werden. Mit steigendem Li-Gehalt in Li2xMg2−xSi ändern sich die Eigenschaften. Der Übergang vom halbleitenden zum metallischen Zustand konnte in dieser Arbeit erstmalig gezeigt werden. In Analogie zu Li2xMg2−xSi konnten die Phasen Li2xMg2−xX (X = Ge, Sn, Pb) charakterisiert werden. Eine Intercalation für Li in Mg2X ist nicht möglich. Die Verbundwerkstoffe basierend auf Mg2Si Das spröde Materialverhalten vonMg2Si-Proben kann durch einen pulvermetallurgisch erzeugten Verbundwerkstoff mit Mg reduziert werden. Die SPS-Technik Basierend auf vorangegangenen Arbeiten konnte innerhalb dieser Arbeit durch die Verwendung von MgH2 die Strom-, Dichte- und Temperaturverteilung während des SPS-Prozesses innerhalb der Probe und des Werkzeuges beurteilt werden.Extensive investigation on selected Mg2Si based materials demonstrate new routes for the application of the SPS technique in respect to basic as well as applied research and provide decisive new material on the characterisation of the Li compounds Li2xMg2-xX (X = Si, Ge, Sn, Pb). Based on prior activities and the results shown in this work new ways of the synthesis using the SPS process (in combination with powder making and processing and suitable tool design) as well as the optimization of material properties of composite materials can be achieved using the SPS technique. The Ternary Phases Mg2Si1−xXx (X = Ge, Sn, Pb) and Mg2−x/2Si1−xSbx For the first the powder metallurgic manufacturing route of the phases Mg2Si1-xXx (X = Ge, Sn und Pb) and the phase Mg2‑x/2Si1-xSbx is shown using the SPS technique and a ball milled powder mixture (MgH2, Si, X). The Ternary Phases Li2xMg2−xX (X = Si, Ge, Sn, Pb) The intercalation of Li into Mg2Si is investigated for the first time by using the SPS solid state reaction based on LiH, MgH2 and Si. The synthesis of the Li poor phase Li2xMg2−xSi could be obtained at temperatures of max. 700 °C. The melting technique made of the elements of these extremely air and moisture sensitive samples could be performed under Argon protective atmosphere followed by a heat treatment at 200 °C. Three different cubic phases of Li2xMg2−xSi can be found on the Mg2Si rich side of the ternary System with the composition in the range of 0 < x < 0,8. With increasing Li content two structural conversions can be found using the x-ray analysis. A change from the space group Fm-3m for Mg2Si via P-43m to P-43m with a superstructure of a′ = 2a could be detected. Linked with the increasing Li content is a change of the properties. The change from the semiconducting behaviour to a metallic characteristic could be shown for the first time. Analogous to Li2xMg2−xSi the phase Li2xMg2−xX (X = Ge, Sn, Pb) could be synthesised and analysed. An intercalation of Li in to Mg2X ist not possible. Composite Materials Based on Mg2Si The brittle behaviour of Mg2Si samples can be reduced by composite material with Mg using the powder metallurgical route. The SPS-Technique Using MgH2 the distribution of the current, the density and the temperature in the sample and tool could be judged.
16
Björk, Lars. "Construction of cooling rig and investigation of cooling sensitivity for aluminum crash alloy." Thesis, KTH, Materialvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-160902.
Full textAbstract:
The work presented in this master thesis deal with the issue of quenching, investigation regarding different cooling rates and its effect on the material properties of aluminum alloy in the 6xxx series used for crash purposes in cars, such as crash boxes, beams and other crash relevant parts. Precipitation of Mg2Si due to different cooling rates affects the material properties such as crash performance, thus the aluminum alloy used is sensitive to different cooling rates. In order to perform tests with different cooling rates a cooling rig was constructed. In order to evaluate the different cooling rates both mechanical testing such as tensile test and 3-point bending test and compression test were performed. Also analyses with scanning electron microscope/energy-dispersive x-ray spectroscopy were performed to estimate grain boundary decoration of Mg2Si due to the different cooling rates. Furthermore LOM analyses were performed to evaluate if the experimental setup had any effect on material properties such as grain size. The constructed cooling rig produced different cooling rates with reliable repeatability as intended. Cooling rates between 130 ̊C/s and 20 ̊C/s were accomplished. Mg2Si occurred in all investigated test samples with various amounts. Higher cooling rates decreases the precipitation of Mg2Si to the grain boundaries, higher cooling rates also increased the bending angle achieved from the 3-point bending test. Furthermore, extensive solution heat treatment at elevated temperatures leads to grain growth.
17
Boudemagh, Djalila. "Synthèse et Etude des Matériaux Thermoélectrique du Système Mg2Si1-XSnX." Phd thesis, Grenoble, 2010. http://tel.archives-ouvertes.fr/tel-00488411.
Full textAbstract:
Le développement de nouveaux composés intermétalliques du système Mg2Si1-xSnx a fait l'objet de recherches intensives en particulier sur leurs propriétés thermoélectriques intéressantes. Les matériaux à base de magnésium sont de bons candidats pour des applications thermoélectriques à des températures moyennes comprises entre 500 et 800 K. Nous nous sommes intéressés dans notre étude à une classe particulière de phases intermétalliques; les phases de Laves caractérisées par des propriétés physiques remarquables en particulier en matière de conductivité électrique intéressante. Des travaux de recherche ont été effectués sur le composé Mg2Si notamment connus pour ses applications thermoélectriques à température moyenne et ont révélé que le dopage de ce composé avec les éléments Sb, Ge et Sn améliore de façon significative les propriétés thermoélectriques de ce matériau. Notre travail consiste à l'élaboration de nouveaux matériaux thermoélectriques en massifs et en couches minces type Mg2Si1-xSnx et d'optimiser leurs propriétés thermoélectriques. L'étude structurale de Mg2Si0,4Sn0,6, Mg2Si et Mg2Sn en fonction de la température ainsi que les affinements des paramètres de maille par la méthode Rietveld sont exposés dans ce travail.
18
Huang, Liwu. "Élaboration, caractérisation et propriétés de stockage d’hydrogène électrochimique des alliages : Mg2Ni1–xMnx (x = 0, 0.125, 0.25, 0.375) et Mg2–xAlxNi (x = 0, 0.25) + 5 wt.% MWCNTs préparés par mécanosynthèse." Thesis, Belfort-Montbéliard, 2012. http://www.theses.fr/2012BELF0173/document.
Full textAbstract:
L’utilisation des combustibles fossiles (énergies non renouvelables) est responsable de l’augmentation de la concentration en gaz à effet de serre dans l’atmosphère. Parmi les solutions de remplacement envisagées, l’hydrogène apparaît comme le vecteur énergétique le plus séduisant. Son stockage dans des intermétalliques permet d’obtenir des capacités massiques et volumiques (e.g. 140 g/L) supérieures à celles obtenues en voie liquide ou sous pression (respectivement 71 et 40 g/L). Dans les accumulateurs Nickel-Métal Hydrure (Ni-MH), l’électrode négative est constituée d’un composé intermétallique qui absorbe l’hydrogène de façon réversible dans des conditions normales de pression et de température. Ce travail de thèse vise d’une part, à synthétiser les alliages Mg2Ni1-xMnx (x =0, 0.125, 0.25, 0.375) et les alliages Mg2-xAlxNi (x = 0, 0.25) avec ou sans nanotubes de carbone (MWCNTs) par mécanosynthèse et d’autre part, d’étudier les effets des substitutions/additions sur la composition et la microstructure des alliages Mg2Ni afin d’améliorer leurs propriétés de stockage d’hydrogène.Les résultats obtenus montrent que les capacités de décharge des alliages Mg2Ni1-xMnx(x = 0, 0.125, 0.25, 0.375) augmentent avec le temps de broyage. Pour l’alliage Mg2Ni0.625Mn0.375 broyé durant 48 h, nous avons mis en évidence la formation d’une nouvelle phase Mg3MnNi2 qui est relativement stable. Par conséquent, Mg3MnNi2 est capable d’améliorer de manière significative la stabilité des cycles tout en maintenant une capacité de décharge relativement élevée.Les résultats obtenus par la théorie de la fonctionnelle de la densité (DFT) en utilisant le programme CASTEP montrent d’une part, que les paramètres de maille et les coordinations atomiques sont en parfait accord avec les résultats expérimentaux. D’autre part, que la stabilité des phases décroit graduellement selon l’ordre suivant : Mg2Ni sans aucune substitution >Mg3MnNi2 > Mg2Ni avec substitution par Mn.L’addition de nanotubes de carbone et de Al ont des effets synergétiques sur la capacité de stockage d’hydrogène électrochimique dans le cas des alliages Mg2-xAlxNi (x = 0, 0.25) + 5 wt.% MWCNTsThe use of fossil fuels (non-renewable energy) is responsible for increasing the concentration of greenhouse gases in the atmosphere. Among the considered alternatives, hydrogen is seen as the most attractive energy vector. The storage in intermetallics makes it possible to obtain mass and volume capacities (e.g. 140 g/L) higher than those obtained by liquid form or under pressure (respectively 71 and 40 g/L). The negative electrode of Nickel-Metal Hydride (NiMH) batteries, is constituted by an intermetallic compound which is able to reversibly absorb hydrogen under normal conditions. In this work, on the one hand, Mg2Ni1-xMnx(x=0, 0.125, 0.25, 0.375) and Mg2-xAlxNi (x = 0, 0.25) electrode alloys with and without multiwalled carbon nanotubes (MWCNTs) have been prepared by Mechanical Alloying. On the other hand, influence of the partial elements substitution on the microstructure and electrochemical hydrogen storage properties of Mg2Ni-type alloy has been studied.The results show that the discharge capacities of Mg2Ni1-xMnx (x =0, 0.125, 0.25, 0.375) alloys increase with the prolongation of milling time. The new phase Mg3MnNi2 is formed only when x=0.375 after 48 h of milling. Mg3MnNi2 phase is relatively stable during charge/discharge cycles and therefore can significantly enhance the cycle stability under simultaneously maintaining a high discharge capacity.Based on the calculated results of first principles, the lattice parameters and atomic coordinates are in good agreement with the experimental results and the stability of phases gradually decreases along the sequence pure Mg2Ni phase > Mg3MnNi2 phase > Mn-substitution doped Mg2Ni phase.When Al and MWCNTs are added simultaneously, the highest discharge capacity is obtained for Mg1.75Al0.25Ni-MWCNTs composite, which implies that MWCNTs and Al have synergistic effects on electrochemical hydrogen storage capacity of milled alloys
19
Grigorova, Eli. "Préparation et caractérisation de matériaux composites à base de magnésium et de Mg2Ni : application pour le stockage de l'hydrogène." Bordeaux 1, 2005. http://www.theses.fr/2005BOR12961.
Full textAbstract:
Parmi les métaux et les intermétalliques pour le stockage de l'hydrogène le magnésium a la plus grande capacité massique, i. E. 7,6%. L'objet de cette thèse est l'étude des propriétés de sorption de l'hydrogène par des composites à base de Mg et/ou Mg2Ni préparés par broyage planétaire. L'influence de la substitution (telle que Mg2Ni1-xMx) et/ou des ajouts de métaux 3d (V, Fe et Co) et de non métaux (graphite) sur ces propriétés est étudiée. Les résultats obtenus montrent que quelque soit le matériau ou le mélange étudié, le broyage planétaire sous atmosphère d'argon ou d'hydrogène permet d'améliorer les cinétiques de sorption. Les échantillons contenant Mg2Ni1-xMx ont une capacité d'absorption élevée même à température moins de 3000C. Les procès d'absorption et de désorption pour tous les composites à base de Mg est plus rapides que dans le cas du Mg pur. Le broyage sous hydrogène notamment dans le cas des mélanges 90% Mg2Ni + 10%V(C) conduit à une amélioration de la désorption par rapport aux mélanges broyés sous argon.
20
Tan, Serdar. "Direct Synthesis Of Hydrogen Storage Alloys From Their Oxides." Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613072/index.pdf.
Full textAbstract:
The aim of this study is the synthesis of hydrogen storage compounds by electrodeoxidation technique which offers an inexpensive and rapid route to synthesize compounds from oxide mixtures. Within the scope of this study, two hydrogen storage compounds, FeTi and Mg2Ni, are aimed to be produced by this technique.
In the first part, effect of sintering conditions on synthesis of FeTi was studied. For this purpose, oxide pellets made out of Fe2O3-TiO2 powders were sintered at temperatures between 900 °C &ndash
1300 °
C. Experiments showed that by sintering at 1100 °
C, Fe2TiO5 forms and particle size remains comparatively small, which improve the reducibility of the oxide pellet. Experimental studies showed that the reduction of MgO rich MgO-NiO oxide pellet to synthesize Mg2Ni occurs only at extreme deoxidation conditions. Pure MgO remains intact after deoxidation. In contrast to these, pure NiO and NiO rich MgO-NiO mixtures were deoxidized successfully to Ni and MgNi2, respectively. Conductivity measurements address the low conductivity of MgO-rich systems as one of the reasons behind those difficulties in reduction. In the last part, a study was carried out to elucidate the low reducibility of oxides. It is considered that the oxygen permeability becomes important when the reduction-induced volumetric change does not yield fragmentation into solid-state. The approach successfully explains why MgO particles could not be reduced at ordinary deoxidation conditions. The study addresses that Mg layer formed at the surface of MgO particles blocks the oxygen transport between MgO and electrolyte as Mg has low oxygen permeability.
21
Vracar, Radivoje. "Développement de matériaux Mg2Si1-xSnx de type n et p pour applications thermoélectriques dans la gamme de température 300-600 °C." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI109.
Full textAbstract:
Des alliages Mg-Si-Sn et Mn-Si, de type n et p respectivement, ont été étudiés pour des applications thermoélectriques dans la gamme de température 20-600 °C. Afin de fabriquer des matériaux denses, un procédé en deux étapes a été développé. La première étape est la fabrication des poudres mères par mécano-synthèse. La deuxième étape consiste en la densification des diverses poudres par la méthode de frittage SPS.En optimisant les conditions opératoires, un ZT de 1.2 a été obtenu à 500 °C pour un matériau de type n de composition Mg2Si0.4Sn0.6. En incorporant de surcroit une faible fraction volumique de nanoparticules de la famille des composés Half-Heusler, il a été possible de fabriquer un matériau présentant au final un ZT de 1.4 à 500 °C. Des liens forts ont été établis entre les paramètres expérimentaux de fabrication, les propriétés thermoélectriques et la microstructure des matériaux frittés (utilisation de la microscopie électronique en transmission).Concernant les études sur le matériau MnSi1.75 de type p, les résultats obtenus ne sont que préliminaires. Néanmoins, en contrôlant là aussi les paramètres de fabrication, un ZT de 0.45 à 575 °C a été obtenu sur un matériau frittéN and P type Mg-Si-Sn and Mn-Si alloys have been investigated for thermoelectrical applications in the 20-600 °C temperature range. To manufacture dense sintered samples, only two steps have been used: mechanical-alloying followed by spark plasma sintering.By optimizing the processing conditions it was possible to obtain an n-Type Mg2Si0.4Sn0.6 material exhibiting a ZT parameter of 1.2 at 500 °C. By adding Half-Heusler nanoparticles to a Mg2Si0.4Sn0.6 matrix, it was shown that the ZT parameter is increased to 1.4 at 500 °C. Then strong links have been established between the processing parameters, the thermoelectrical properties and the sintered microstructure (use of transmission electron microscopy).The investigations performed on a p-type MnSi1.75 material are only preliminary ones. Nonetheless, always by tailoring the processing conditions, it was possible to obtain a sintered material exhibiting a ZT parameter of 0.45 at 575 °C
22
Huang, Liwu. "Élaboration, caractérisation et propriétés de stockage d'hydrogène électrochimique des alliages : Mg2Ni1-xMnx (x = 0, 0.125, 0.25, 0.375) et Mg2-xAlxNi (x = 0, 0.25) + 5 wt.% MWCNTs préparés par mécanosynthèse." Phd thesis, Université de Technologie de Belfort-Montbeliard, 2012. http://tel.archives-ouvertes.fr/tel-00720661.
Full textAbstract:
L'utilisation des combustibles fossiles (énergies non renouvelables) est responsable de l'augmentation de la concentration en gaz à effet de serre dans l'atmosphère. Parmi les solutions de remplacement envisagées, l'hydrogène apparaît comme le vecteur énergétique le plus séduisant. Son stockage dans des intermétalliques permet d'obtenir des capacités massiques et volumiques (e.g. 140 g/L) supérieures à celles obtenues en voie liquide ou sous pression (respectivement 71 et 40 g/L). Dans les accumulateurs Nickel-Métal Hydrure (Ni-MH), l'électrode négative est constituée d'un composé intermétallique qui absorbe l'hydrogène de façon réversible dans des conditions normales de pression et de température. Ce travail de thèse vise d'une part, à synthétiser les alliages Mg2Ni1-xMnx (x =0, 0.125, 0.25, 0.375) et les alliages Mg2-xAlxNi (x = 0, 0.25) avec ou sans nanotubes de carbone (MWCNTs) par mécanosynthèse et d'autre part, d'étudier les effets des substitutions/additions sur la composition et la microstructure des alliages Mg2Ni afin d'améliorer leurs propriétés de stockage d'hydrogène.Les résultats obtenus montrent que les capacités de décharge des alliages Mg2Ni1-xMnx(x = 0, 0.125, 0.25, 0.375) augmentent avec le temps de broyage. Pour l'alliage Mg2Ni0.625Mn0.375 broyé durant 48 h, nous avons mis en évidence la formation d'une nouvelle phase Mg3MnNi2 qui est relativement stable. Par conséquent, Mg3MnNi2 est capable d'améliorer de manière significative la stabilité des cycles tout en maintenant une capacité de décharge relativement élevée.Les résultats obtenus par la théorie de la fonctionnelle de la densité (DFT) en utilisant le programme CASTEP montrent d'une part, que les paramètres de maille et les coordinations atomiques sont en parfait accord avec les résultats expérimentaux. D'autre part, que la stabilité des phases décroit graduellement selon l'ordre suivant : Mg2Ni sans aucune substitution >Mg3MnNi2 > Mg2Ni avec substitution par Mn.L'addition de nanotubes de carbone et de Al ont des effets synergétiques sur la capacité de stockage d'hydrogène électrochimique dans le cas des alliages Mg2-xAlxNi (x = 0, 0.25) + 5 wt.% MWCNTs.
23
Olmez, Rabia. "Combinatorial Study Of Hydrogen Storage Alloys." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/2/12610552/index.pdf.
Full textAbstract:
A combinatorial study was carried out for hydrogen storage alloys which involve processes similar to those normally used in their fabrication. The study utilized a single sample of combined elemental (or compound) powders which were milled and consolidated into a bulk form and subsequently deformed to heavy strains. Material library was obtained in a post annealing treatment carried out at elevated temperatures which brings about solid state reactions between the powders yielding equilibrium phases in the respective alloy system. A sample comprising the material library was then pulverized and screened for hydrogen storage composition. X-ray diffraction was used as a screening tool, the sample having been examined both in as-processed and hydrogenated state. The method was successfully applied to Mg-Ni, and Mg-Ni-Ti yielding the well known Mg2Ni as the storage composition. It is concluded that partitioning of the alloy system into regions of similar solidus temperature would be required to enrich the material library.
24
Hu, Fang. "Synthesis and Characterization of Magnesium-Silicon and Magnesium-Tin Solid Solutions for Thermoelectric Applications." Thesis, 2012. http://hdl.handle.net/1969.1/ETD-TAMU-2012-05-11128.
Full textAbstract:
The environmentally friendly n-type Mg2(Si, Sn) thermoelectric solid solutions have a strong potential of commercial utilization in thermoelectric (TE) energy conversion due to their availability, low density (~3.02 g/cm3), and high stability at middle temperature range (400-600 ▫C) that are typically observed from waste heat dissipating systems. The bulk materials were prepared from element powders via slow cooking under vacuum condition and current-assisted hot-press sintering. Temperature vs time curves have been researched in this thesis for fully reacted magnesium-silicide & magnesium-stannide green ingots with doping materials i.e. antimony, bismuth by different doping ratios. These ingots were ground by a high energy ball miller, uniaxial cold pressed into half inch pallets and then sintered by Direct Current-assisted hot pressing. Different synthesis conditions such as ball milling, sintering time, pressure, have been compared by SEM images and XRD tests analysis to figure out optimized process parameters. Several samples’ thermal conductivities (κ) were plotted as a function of temperature to study different synthesis strategies and doping materials’ effects on phonon scattering inside bulk thermoelectric materials.
25
"STUDY OF Mg2Si-BASED THERMOELECTRIC MATERIALS." Thesis, 2016. http://hdl.handle.net/10388/ETD-2016-04-2528.
Full textAbstract:
Mg2Si-based thermoelectrics are currently the most promising, environmentally benign and inexpensive materials for power generation. The objective of this thesis is to characterize Mg2Si-based thermoelectric materials using state-of-the-art synchrotron radiation techniques including infrared reflectivity/absorption spectroscopy and high resolution X-ray powder diffraction. This is complemented by density functional theory (DFT) calculations. Also reported here is the main research: the analysis of the electronic structure and transport properties of doped Mg2Si using experimental and theoretical methods.
To enhance the thermoelectric performance, Mg2Si doped with a single component of Bi or Sb were studied. The investigation showed by doping the electron carrier concentrations were increased. In particular, dc conductivities of the doped samples were extracted from the analysis of infrared reflectivity spectra employing the Drude free electron model. We found the conductivity was lower when determined by infrared measurements rather than in-situ four point probe measurements of the bulk sample because of the limited penetration depth of infrared (IR) radiation and the very small spot size. In particular, we were able to extract the electrical conductivity, relaxation times and electron effective masses of the samples. DFT calculations reproduced the experimental observations and show a substantial increase in the Seebeck coefficients.
The next step was to study the effect after doping with two different dopants. For this purpose, we investigated the effect of Ge substitute Si in Bi doped Mg2Si. In particular, the dc conductivities of the doped samples were extracted from the analysis of infrared reflectivity spectra. From the IR data, we extracted the relevant parameters for electrical transport. The experimental data were explained with theoretical DFT calculations in which the calculated densities of states (DOS) of the Ge- and Bi-doped Mg2Si samples were found to be very similar, and therefore to have comparable Seebeck coefficients. The steep curvatures of the DOS at the Fermi level indicate a light electron band. We found the thermal conductivity of Mg2Si is substantially lower from 7 Wm-1K-1 to 2.7 Wm-1K-1 in Mg2Si0.677Ge0.3Bi0.023 at 300 K. A performance figure of merit of 0.7 was achieved at 773 K for this sample.
We further investigated the effect of multi-doping with Sb, Al and Zn on the enhancement of the thermoelectric and electrical transport properties of Mg2Si. A maximum ZT of 0.964 was found for Sb0.5%Zn0.5% doped Mg2Si (Mg1.995Zn0.005Si0.995Sb0.005) at 880 K. This value is comparable to those of PbTe based thermoelectrics which are the currently the materials used in commercial products.
We also studied the effect of pressure on the thermoelectric performance of a Al-doped Mg2Si sample. From in-situ X-ray diffraction, we observed a structural transform in which the electrical conductivity was increased after the phase transition. The experimental observed maximum thermoelectric power at 1.9 GPa was reproduced by DFT calculations and explained by the increase of electronic density of states at the Fermi level.
The effect of multi-wall carbon nanotubes (MWCNTs) to increase the electrical conductivity of Mg2Si0.877Ge0.1Bi0.023 was examined. At 323 K the conductivity was found to increase from 450 Ω-1cm-1 to 500 Ω-1cm-1. However, this effect diminished at higher temperature and the conductivity drop to 470 Ω-1cm-1 at 773 K. Raman study showed the persistent of disorder (D) and tangential (G) mode characteristics of a carbon nanotube in the doped sample indicating that there was no decomposition or substantial chemical reaction of the MWCNTs with Mg2Si0.877Ge0.1Bi0.023.
Finally, we present the results on the analysis of valence electron topologies of Mg2Si multi-doped with Al, Zn and Sb thermoelectric materials by the Maximum Entropy Method (MEM) using data obtained from synchrotron X-ray powder diffraction measurements. The results showed the qualitative feature of valence electron distributions were correctly located. However, due to the limited number of Bragg diffraction peaks in the experimental patterns, the effect of the dopants to the core charge density cannot be reliably obtained. An error analysis was performed from the analysis of diffraction pattern of Al-doped Mg2Si which included high angle Bragg reflections. We concluded that the density maps extracted from MEM analysis of the doped samples were qualitatively correct.
26
ChinYang and 楊覲. "Powder preparation and thermoelectric properties of Mg2Si-based materials." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/4857sm.
Full textAbstract:
碩士國立成功大學
材料科學及工程學系
103
Due to the difference of melting point amomg Mg, Si and Sb elements, it is not easy to synthesize Mg2Si -based alloy by melting method. In this study, Mg2Si-based thermoelectric bulks were fabricated by solid-state reaction and hot-pressed sintering (HP, SPS). The results show that with the increase of Sb-doping in Mg2Si, the electrical conductivity (σ) increase, and the Seebeck coefficient increase slightly at higher temperature. The power factor of Mg2Si -based bulks was improved by Sb doping. The maximum value of the power factor, PF, is 1.03 mW/m-k2 at 765K for the Mg2.16(Si0.4Sn0.6)0.975Sb0.025 bulk.
27
Huang, Tzu-Yun, and 黃子耘. "Solid State Synthesis and Characterization of Sn-doped Mg2Si Thermoelectric Materials." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/63938182705402359411.
Full textAbstract:
碩士國立交通大學
材料科學與工程學系所
104
Magnesium silicide (Mg2Si) which is an inorganic compound consisting of low-cost and nontoxic magnesium and silicon has become one of the most promising thermoelectric materials as lead telluride (PbTe) mainly due to its high Seebeck coefficient and low thermal conductivity. The Sn doping has been proven as an effective strategy not only to overcome the problem of the very low electric conductivity of intrinsic Mg2Si, but to further decrease the thermal conductrivity and thus the overall thermoelectric figure of merit (ZT). In this work, Mg2Si and Sn-doped Mg2Si were synthesized using high-temperature solid-state approaches. The raw materials of Mg, Si, and Sn powders were ball-milled and were then heated at different temperatures. To prevent the formation of oxides which would seriously decrease ZTs, a variety of processing parameters were verified. It has been found that the oxide-less product can be achieved using sealed quartz tubes. The synthesized optimized Mg2Si0.4Sn0.6 bulk exhibits relatively better thermoelectric properties at 470 K where the Seebeck coefficience is -145 μV/K, the electrical conductivity is 4.4 S/cm, and thus the calculated power factor is 9.310-2 μW/cm-K2. In addition, the measured x-ray power diffraction (XRD) patterns comprising multiple Mg2SixSn1-x phases were refined with the Rietveld method not only for quantitatively characterizing the fraction of the targeted Mg2Si0.4Sn0.6 compound, but for providing the experimental relation between the lattice constant and the ratio of Sn/Si of the Mg2SixSn1-x compounds.
28
Uyma, Falko. "Untersuchungen auf dem Gebiet der Al-Mg-Si- und Al/Mg2Si-in-situ Legierungen." Doctoral thesis, 2006. https://tubaf.qucosa.de/id/qucosa%3A22678.
Full textAbstract:
Das Ziel dieser Arbeit bestand in der Entwicklung eines Werkstoffes auf Basis der Legierung AlSi13,5Mg9,5 (=Al-15Mg2Si-8Si), die sich durch ein verbessertes Verschleißverhalten, geringere thermische Ausdehnung und geringere Dichtewerte auszeichnet. Eine wesentliche Aufgabe der Arbeit bestand in der Einstellung bester mechanischer Eigenschaften durch die Feinung der Primär-Phase (Mg2Si) sowie durch Mikrolegieren. Ausbleibende Resultate begründeten die Wahl einer angepassten Legierungszusammensetzung AlMg8,6Si6,4 (=Al-14Mg2Si-1Si). Versuche zur Eigenschaftsoptimierung (Mikrolegieren, Wärmebehandlung) zeigten neben der Ermittlung der gießtechnischen Eigenschaften die spezifischen Legierungscharakteristika auf. Die Verarbeitung des optimierten Werkstoffes mit verschiedenen Verfahren machte die Abhängigkeit der Ausbildung der mechanischen Eigenschaften sowie des Gefüges deutlich. Die Untersuchung der thermo-physikalischen Eigenschaften sowie die Analyse der Wechselwirkungen zwischen Risswachstum und Gefüge runden die Beschreibung des Eigenschaftsprofiles ab.
29
Wu, Kun-Da, and 吳昆達. "Effect of Mn on the Microstructure and Wear Properties of Al-13.9wt.%Mg2Si Composites." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/18894008507110224586.
Full textAbstract:
碩士國立中央大學
機械工程學系
104
With microstructure observation and mechanical test,explore the effect of manganese on wear properties of Al-13.9wt.% Mg2Si (Al-8.8Mg-5.1Si (wt%)) composites. The result indicated that unmodified cast material mainly observed primary α-Al , primary Mg2Si particles and lamellar eutectic Mg2Si.However the cast material with manganese observed finer aluminum grain, primary Mg2Si particles and fibrous eutectic Mg2Si.After homogenization treatment, the eutectic Mg2Si are both transformed into fine spherical shape. Addition of manganese in Al-13.9wt.% Mg2Si composites not only enhance the hardness and tensile strength of the cast material,but also reduce the wear surface degree of delamination.After homogenization treatment, whether or not with manganese, it didn’t affect the hardness,but significantly enhance the ductility of both materials. The tensile fracture surface are observed little dimple. The wear surface are both rendered wave pattern and the wave pattern of the manganese-containing material is relatively dense,it shows a high abrasion impedance of manganese material.
30
Uyma, Falko [Verfasser]. "Untersuchungen auf dem Gebiet der Al-Mg-Si- und Al/Mg2Si-in-situ-Legierungen / von Falko Uyma." 2006. http://d-nb.info/983682291/34.
Full text
31
Chen, Jun-Yu, and 陳俊宇. "The feasibility of preparing Mg2Sn alloy by mechanical alloying." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/fpb487.
Full textAbstract:
碩士國立臺灣海洋大學
材料工程研究所
105
In this study, we attempted to prepare Mg67Sn33 compound powder by high energy ball milling process. The phase formation inside the as-milled powders was analyzed by SEM, XRD, and DSC. The experimental results show that there were pure element peaks for 15 minutes powders, but the Mg2Sn (Cubic) equilibrium phase was also successfully synthesized at the beginning of the milling. After ball milling time was extended to 30 minutes, the magnesium element peaks completely disappeared and the presence of the Mg2Sn (Orthorhombic) non-equilibrium phase began in the alloy powder, then the proportion of non-equilibrium phase increases as time increases. Finally, the ball milling time achieved 240 minutes, the alloy powder was based on Mg2Sn (Orthorhombic) non-equilibrium phase, was not the Mg2Sn (Cubic) equilibrium phase. After the heat treatment showed that the non-equilibrium phase transformed into equilibrium phase, Therefore, it was assumed that the mechanical energy produced by ball milling lead to the Mg2Sn (Cubic) phase to be converted into Mg2Sn (Orthorhombic) phase. Non-equilibrium phase was an unstable alloy phase and gave some of thermal energy it could transform equilibrium phase, would lead to the above-mentioned XRD results. However, the DSC results were also similar to the XRD analysis. The 15 minutes powder with an endothermic peak occurring at about 203℃. Mg2Sn (Cubic) phase had been found in the powder by determining the Mg2Sn equilibrium phase from the Mg-Sn phase diagram, where the eutectic reaction was converted into the liquid phase. However, an exothermic peak was generated in the vicinity of 170 ° C in the alloy powder for 120 minutes and 240 minutes. Due to XRD analyzed the heat treated powder at 170 ° C found that the non-equilibrium phase was converted into the equilibrium phase, it could prove why the DSC result had a exothermic reaction at 170℃. Although it was a successfully synthesized of Mg2Sn phase, but alloy powder still had a few tin elements, according to other literatures found two ways to make tin disappeared, one was to increase the milling time, the other was to add excessive magnesium achieved the goal of complete alloying.
32
Hu, Hsien-Chung, and 胡賢君. "Effect of LaNi5 additions on electrode properties of Mg2Ni alloys." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/88492821733492087851.
Full textAbstract:
碩士國立中央大學
材料科學與工程研究所
99
Mg2Ni alloys were prepared by Isothermal Evaporation Casting Process (IECP) and LaNi5 were prepared by Arc-melting. These two alloys were mixed by Ball-milling with different amount of LaNi5 and milling time. Discharge capacity and discharging cycle life were discussed by structure analyzing and Battery Testing System. As a result, the discharge capacity of Mg2Ni was increased with the ball milling time increased. Mg2Ni ball milled with LaNi5 with a long time (such as 6 hr) could increase the rate of tending to amorphousness, but could not increase the cycle life of alloy. We mixed the 24-hour ball-milled LaNi5 with Mg2Ni at different mixing time and mount of LaNi5 by ball-milling. The best mixing time of ball-milling was 30 second. Moreover, the cycle life of Mg2Ni was increased if the additive amout of LaNi5 was over 20 wt.%.
33
Kannan, Subburaj. "Molecular characterization of rat cardiac sarcolemmal Ca2S+/Mg2S+ ecto-ATPase." 1998. http://hdl.handle.net/1993/1375.
Full textAbstract:
Sarcolemmal Ca$\sp{2+}$/Mg$\sp{2+}$ ecto-ATPase (Myoglein; MW 180 kD) is a membrane bound enzyme which requires millimolar concentrations of either Ca$\sp{2+}$ or Mg$\sp{2+}$ for maximal hydrolysis of ATP. In order to elucidate the structural and functional properties of the rat cardiac sarcolemmal Ca$\sp{2+}$/Mg$\sp{2+}$ ecto-ATPase, this protein was purified to homogeneity and utilized for the biophysical, molecular and immunochemical characterization. Mass spectroscopic analysis of the enzyme using different matrix combinations revealed the presence of multi-components indicating microheterogeneity in the protein structure. Treatment of the ecto-ATPase with DL-dithiothreitol did not alter the pattern of mass spectroscopic analysis and this indicated that the microheterogeneity may be due to some posttranslational modifications. For determining the molecular structural properties, the purified Ca$\sp{2+}$/Mg$\sp{2+}$ ecto-ATPase was subjected to tryptic digestion and amino acid sequencing. The amino acid sequence was utilized to design an oligonucleotide probe. Screening of a rat heart cDNA library produced a partial cDNA clone (pND2.1) that was 100% homologous to human platelet CD36. A high degree of homology ($>$70%) with other cell adhesion molecules was also noted. The oligomer probe detected a 4.4 kB transcript in heart, brain, spleen, lung, liver, skeletal muscle, kidney, and testis. An additional 3.1 kB transcript was detectable in heart, lung, liver and skeletal muscle while transcripts of $\sim$2.0 kB and $\sim$1.0 kB were also evident in the heart whereas ND2.1 detected a $\sim$3.1 kB transcript in cardiac tissue. To determine the immunochemical properties of the rat cardiac Ca$\sp{2+}$/Mg$\sp{2+}$ ecto-ATPase, a polyclonal antiserum was raised against purified $\rm Ca\sp{2+}$/Mg$\sp{2+}$ ecto-ATPase. As assessed by Western blot analysis, the antiserum as well as the purified immunoglobulin were specific for Ca$\sp{2+}$/Mg$\sp{2+}$ ATPase; no crossreaction was observed towards other membrane bound enzymes such as rat sarcoplasmic reticulum Ca$\sp{2+}$-pump ATPase or plasma membrane Ca$\sp{2+}$-pump ATPase On the other hand, the cardiac Ca$\sp{2+}$/Mg$\sp{2+}$ ATPase was not recognized by either rat SR Ca$\sp{2+}$ ATPase or liver ecto-ATPase (Ca$\sp{2+}$/Mg$\sp{2+}$ ATPase) antibodies. In this study, we have produced an antiserum which is specific for plasma membrane Ca$\sp{2+}$/Mg$\sp{2+}$ ecto-ATPase in cardiocytes. This antiserum can localize the plasma membrane of cardiomyocytes as well as brain, skeletal muscle, liver and kidney. Western immunoblots revealed that a polyclonal antiserum raised against the purified cardiac Ca$\sp{2+}$/Mg$\sp{2+}$ ecto-ATPase in rabbit recognized the CD36 molecule, whereas a monoclonal antibody directed against human CD36 cross-reacted with cardiac Ca$\sp{2+}$/Mg$\sp{2+}$ ecto-ATPase, in cardiac plasma membrane preparation. On the basis of these observations, the role of the Ca$\sp{2+}$/Mg$\sp{2+}$ ecto-ATPase in cell adhesion phenomenon was tested by carrying out a cell-cell adhesion bioassay in neonatal cardiomyocyte culture. The purified IgG fraction of the anti-cardiac Ca$\sp{2+}$/Mg$\sp{2+}$ ecto-ATPase serum was found to depress the spreading and attachment of cardiomyocytes to their substratum. These results suggest that the rat cardiac Ca$\sp{2+}$/Mg$\sp{2+}$ ecto-ATPase is an acidic protein having two subunits. Furthermore, Ca$\sp{2+}$/Mg$\sp{2+}$ ecto-ATPase shows microheterogeneity in its molecular structure. It is concluded that rat cardiac Ca$\sp{2+}$/Mg$\sp{2+}$ ecto-ATPase may either contain a fragment with cell adhesion properties or is tightly associated with a protein which is homologous to the adhesion molecule CD36. (Abstract shortened by UMI.)
34
Hannah, Mark E. "Mechanism for long persistent phosphorescence in Sr₂MgSi₂O₇:Eu²⁺." 2008. http://purl.galileo.usg.edu/uga%5Fetd/hannah%5Fmark%5Fe%5F200812%5Fms.
Full text
35
Lin, Chun-Yu, and 林峻右. "Effect of Mg3MnNi2 on the electrochemical and hydrogenation properties of Mg2Ni alloy." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/92353164022956185726.
Full textAbstract:
碩士國立中央大學
材料科學與工程研究所
96
Mg3MnNi2-Mg2Ni alloy systems with different ratio is produced by an innovative method, isothermal evaporation casting process (IECP) in this work. The effects of Mg3MnNi2(β phase) on the electrochemical and hydrogenation properties of Mg2Ni(γ phase) alloy were investigated. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and X-ray diffraction (XRD) analyses demonstrate that mass production for Mg3MnNi2-Mg2Ni alloy systems with different ratio was successfully fabricated by IECP. It is observed that HCP-Mg2Ni (γ phase) and FCC-Mg3MnNi2 (β phase) have nearly oxidation/reduction potential and their absorption/ desorption pressure plateaus are similar. It is also found by X-ray photoelectron spectroscopy (XPS) that addition Mg3MnNi2 in Mg2Ni alloy reduced the passive Mg(OH)2 layer formation and led to discharge capacity, discharge efficiency and discharge cycle life improving. It is found that it is difficult to corroded in alkaline electrolyte and hydrogenation for Mg3MnNi2 in comparison with Mg2Ni. It is caused Mg3MnNi2 addition in Mg2Ni resulted in an improvement for electrochemical properties and a deceleration for hydriding-dehydriding rate.
36
Chiang, Chien-chang, and 江建璋. "ffects of Ag on hydrogen storage properties and electrochemical performances of Mg2Ni alloy." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/78263467078445932947.
Full textAbstract:
碩士國立中央大學
機械工程研究所
96
A different ratio of Ag has been added in Mg2Ni by isothermal evaporation casting process (IECP) and ball milling. To research the effects of Mg-Ni-Ag alloys on the hydrogen storage properties and discharge capacity when Ag addition in Mg2Ni with different types (compounds or elements). A high purity Mg2Ni alloy will be fabricated by IEC-process. There are two phases appeared (partial Ag substituted Mg2Ni and partial Ni substituted Mg3Ag) in Ag added Mg2Ni. The hydrogen storage capacity decrease with sliver content increasing, but hydrogen absorption rate has not improved. The PCI curves show two plateaus in Ag added Mg2Ni. It is found that the hydriding mechanism of the first plateau is Mg2Ni alloy hydrogenation. The second plateau guesses partial Ni substituted Mg3Ag alloy hydrogenation. Ag addition was no effect on the discharge properties. In ball milling, there are similar results for broaden and weakened Mg2Ni and Ag peaks after ball milling 2 hours and 5 hours by X-ray diffraction (XRD). There is the new phase MgAg formed in ball-milled Mg2Ni + 20wt.% Ag alloy after annealing. The maximum hydrogen storage capacity of Mg2Ni alloy reached 2.9 wt.%, but the capacity of Mg2Ni +20wt.% Ag alloy only reached 2.0 wt.%. The capacity decrease is because of the MgAg phase formation. Discharge capacity upgraded to 100 mAh / g after Mg2Ni alloy ball-milled. Ag addition can improve cycle life by ball milling, but the maximum discharge capacities was been reduced.
37
Costa, José Carlos Gonçalves. "MGPSI – Metodologia de gestão de projectos aplicada ao desenvolvimento de sistemas de informação." Master's thesis, 2010. http://hdl.handle.net/10362/13314.
Full textAbstract:
No domínio da concepção e desenvolvimento de sistemas de informação, é vulgar encontrar projectos que estão nas seguintes situações: não cumprem prazos; ultrapassam os orçamentos previstos; têm um nível de qualidade baixo. Esta última situação irá reflectir-se, posteriormente, na manutenção dos referidos projectos.
Estudos efectuados concluem que há várias causas para que tais factos ocorram e entre as principais está a ausência de uma metodologia de gestão de projectos.
Assim, uma solução que permita minimizar as situações supracitadas passa pela criação e implementação de uma metodologia de gestão de projectos aplicada ao desenvolvimento de sistemas de informação. Esta metodologia contribuirá para optimizar a gestão e aumentar a produtividade das equipas de projecto, e, consequentemente, incrementar o nível de maturidade da gestão de projectos.
Na análise do trabalho relacionado, identificaram-se os seguintes pontos fracos: não identificação e clarificação de uma atribuição inicial de processos e actividades a projectos e não existência de uma caracterização inicial do projecto. Outros pontos fracos, embora menos recorrentes, foram a inexistência de versões de processos e insuficiente informação sobre a constituição de uma base de dados de conhecimento da gestão de projectos.
O objectivo principal desta dissertação consistiu em conceber, implementar e avaliar, num organismo público, uma metodologia de gestão de projectos aplicada à concepção e desenvolvimento de sistemas de informação.
Assim, criou-se e simulou-se um modelo com vários subprocessos e actividades, usando ferramentas de gestão de processos de negócio. A implementação traduziu-se na criação de um portal, contendo um sistema de informação com um conjunto inicial de procedimentos, para se garantir uma gestão integrada de projectos.
38
Lin, Tsung-Hsiung, and 林琮雄. "Preparation and Hydrogen absorption performance of Mechanically Alloyed (Mg2Ni)X(FeTi)100-X Powder." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/56352165887420787650.
Full textAbstract:
碩士逢甲大學
材料科學所
100
In the present study, mechanical alloying process was used to synthesize FeTi and Mg2Ni alloy powder separately. FeTi and Mg2Ni alloyed powders were then mixed according to (Mg2Ni)x(FeTi)100-X (x =10, 30, 50, 70, and 90) to prepare composite alloy powder. The as-milled powder as a function of milling time were examined and analyzed by XRD, XAS, SEM, hydrogen storage kinetics curves, and P-C-T curves, etc. After three hours of ball milling, FeTi alloy powder transformed into FeTi intermetallic compound. The grain size of as-milled powder decreased with increased milling time. After fifteen hours of ball milling, the as-milled powder consisted of Fe, Ti, FeTi intermetallic, and amorphous phases. The hydrogen storage capacity of 15h milled FeTi powder can achieve 0.4 wt.%. For (Mg2Ni)x(FeTi)100-X powder, the hydrogen absorption ability was 1.56 wt.% for 50 at.% Mg2Ni alloy powder. It increased to 2.45 wt.%. when 90 at.% Mg2Ni was added. Hydrogen storage increased with increasing amount of Mg2Ni. On the other hand, the presence of FeTi will decrease the hydrogen storage capacity. Whereas, FeTi can accelerate the hydrogen absorption rate. Surface morphology observation by SEM revealed that adding FeTi can prevent effectively the powder agglomeration and be beneficial to hydrogen absorption rate. All the as-milled powder tested by hydrogen absorption transformed into Mg2NiH4 phase and hydrogen embrittlement can be noticed. Keywords：mechanical alloying, kinetics curves , intermetallic compound, amorphous, hydrogen storage
39
Lin, Shian-Ke, and 林賢科. "The study of mechanical alloyed Mg2Ni/Ag composite powder and its hydrogen storage properties." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/66922785027488000898.
Full textAbstract:
碩士逢甲大學
材料科學所
94
Applying hydrogen storage alloys to store and transport hydrogen is a newly developed technique. Among various ways for hydrogen storage, metal hydrides have the advantages of relatively small volume, low pressure, and safety. The A2B type Mg2Ni intermetallic due to its high hydrogen absorption capacity, lightweight and low cost is considered as a promising candidate for hydrogen storage applications. In this study, various silver contents were added into Mg2Ni matrix. An intermetallic powder with a desired composition of (Mg2Ni)100-xAgx (x=0, 0.5, 1.0, 2.5, and 5.0) was directly prepared by mechanical alloying from pure Mg, Ni, and Ag elemental powders under a inert gas. Besides, water cooling system was also applied to prepare non-added Mg2Ni powder during MA for comparing with conventional MA process. The structural transformations of as-milled powder mixtures varied with milling times were examined by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). The experimental results showed that the 15h as-milled powders were identified as a nanocrystalline mixture of Mg2Ni, Mg, Ni and amorphous phase. It is also noted that the amorphous phase will be recrystallized under prolonged milling. In addition, the hydrogen storage kinetics, pressure-composition-temperature (P-C-T) curves and thermal analysis of 15h milled powders were evaluated. Silver addition significantly improved the hydrogen absorption capacity of Mg2Ni, revealing that the maximum and reversible hydrogen capacities at 350°C were increased from 3.14 to 3.93 wt.% and from 2.40 to 3.13 wt.%, respectively, for the 15h milled Mg2Ni powder at silver content of 0.5 at.%. For the Mg2Ni powder prepared from water cooled MA process, the maximum and reversible hydrogen capacities at 350°C were increased from 3.14 to 3.83 wt.% and from 2.40 to 3.03 wt.%, respectively. The hydride formation heat of (Mg2Ni)99.5Ag0.5 powder is –59.7 kJ/mol H2, that is betterthan the reported values (−64.5 kJ/mol H2). And the hydrides decomposition temperature decreased to 190°C, as compared to 220°C of Mg2Ni. In this study, the addition of silver into Mg2Ni matrix and the decrease of milling temperature for Mg2Ni powders in MA obviously improved their hydrogen storage properties.
40
Lin, Ci-Siang, and 林琪翔. "Thermal-Fluid Behavior and Design of Heat Transfer Ehancement for Mg2Ni Hydride Storage Canisters." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/55048379603103422955.
Full textAbstract:
碩士國立中央大學
能源工程研究所
97
A study of the hydrogen absorption and desorption processes using Mg2Ni hydrogen storage alloy is presented for investigation on the thermal-fluid behavior in canister and influences of canister geometry. Absorption and desorption reaction rates and equilibrium pressures are calculated by fitting experimental data in literature using least-squares regression. Then, the fitted parameters are used in the simulations for the thermal-fluid behavior of hydrogen storage canisters. Since the alloy powders will expand in absorption, and shrink in desorption, the canisters in question comprise a metal bed and expansion volume. To enhance heat transfer, we consider the canisters to be equipped with a air pipe at the centre line and/or with internal fins. Simulation results show the bare cylindrical canister can not carry out during two hours absorption or desorption reactions, but the canister with the addition of a concentric heat exchanger pipe with fins can complete absorption or desorption reactions during about 6000 s. Results also show the reaction rates can be further increased by adjusting working parameters For absorption processes, it benefit by reducing surrounding temperature, increasing inlet pressure or increasing flowing air velocity. For desorption processes, the reaction rate can be increased by increasing surrounding temperature, reducing outlet pressure or increasing flowing air velocity. Finally, adjusting the internal fin volume shows that it is the fin volume that principally affects the heat transfer enhancement of the hydride canister.
41
Huang, T. W., and 黃宗偉. "Experiments, Simulation and Heat Transfer Analysis on Hydrogen Absorption/Desorption in Mg2Ni Metal Hydride Systems." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/52402081525836814209.
Full textAbstract:
碩士國立臺灣海洋大學
機械與機電工程學系
96
Most studies in the literature dealt with minute quantity of Mg-based metal hydrides (such as Mg2Ni). This work investigated the absorption/desorption capability of a practical (1kW) hydrogen storage tank filled with 4.5kg Mg2Ni. A comparison and related discussion was made between numerical and experimental results. Two types of reaction tanks were considered in this study, namely, a electric-heating tank and a gas-heating tank. The latter one closely simulates use of the waste heat coming from gas power plants. In the aspect of electric-heating reaction tank, the numerical results indicated that under the condition of charging pressure of 17 bar and wall temperature of 150℃, the hydrogen absorbed in 150 minutes could reach 83 moles, equivalent to the theoretical value of hydrogen absorption (18.4 mole/kg) for 4.5kg Mg2Ni. It was also shown that the effect of pressurized cooling water was not so significant. Moreover, the reaction tank could release hydrogen up to 90% of the theoretical value of hydrogen absorption in 150 minutes. As for the experimental work for the electric-heating reaction tank, due to non-uniform grain size of Mg2Ni powder as well as frequent malfunction of some control valves, the activation results were below expectation. The other type of the reaction tank considered in this study is of the form of a double-pipe design, which contains 4.5kg Mg2Ni in the inner pipe while hot or cool air flows in the finned space between the inner pipe and the outer pipe. Use of fins is to increase the heat transfer area and to fulfill the cooling/heating requirement during hydrogen absorption/desorption processes. Due to uniformly small size (below 1mm) of Mg2Ni, the absorption/desorption capability of the gas-heating tank reached 75% to 77% of the theoretical value (18.4 mole/kg). Both numerical simulations and experiments were conducted for this tank. The results were qualitatively in agreement with the numerical results for the electric-heating tank. Finally, the reaction tank was connected to a 1 kW fuel cell with a hydrogen storage buffer tank in between. As the pressure inside the buffer tank reaches a pre-set value, hydrogen is then released to drive the fuel cell. It was found that the fuel cell worked well in connection with the gas-heating tank. The results obtained in this study will be helpful in developing more practical hydrogen-electricity systems.
42
Jhang, Yu-Hao, and 張育豪. "Analysis of Wall Strain on the Reaction Vessel of Mg2Ni Alloy During Cyclic Hydriding/Dehydriding Processes." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/11733591969566871696.
Full textAbstract:
碩士國立中央大學
機械工程研究所
96
The purpose of this study is to investigate the wall strain variation on the reaction vessel of Mg2Ni alloy at various combinations of location and direction during cyclic hydriding/dehydriding processes. The reaction vessel was made of AISI 316 stainless steel. The pressure conditions for the absorption and desorption steps were set at 3 MPa and vacuum, respectively, at 300 oC. The particle morphology of the Mg2Ni alloy before activation and after a 45-cycle test was analyzed with scanning electron microscopy (SEM). Results showed that the strain accumulation phenomenon in the hoop strain disappeared at the later hydriding/dehydriding cycles due to agglomeration of the Mg2Ni alloy powders no matter at the location of 1/10 or 3/10 height of the vessel. The cycle number at the disappearance of the strain accumulation phenomenon in the hoop strain at the location of 1/10 height of the vessel was smaller than that of the 3/10 height by 5 cycles. This was ascribed to a continuous increase in the height of an agglomerated disk formed at the bottom of the reaction vessel. With regard to the strain increment in a hydriding/dehydriding cycle, the hoop strain increment was drastically reduced toward zero at the later testing cycles while the axial strain increment was gradually reduced in a smaller rate throughout the test. This could be attributed to less and less absorption activities taking place in the continuously growing agglomerated Mg2Ni alloy disk formed at the bottom of the reaction vessel. The SEM observations showed that a pulverization mechanism caused not only the corners of the Mg2Ni alloy powders to change from sharp to smooth and round but also the particle size of the Mg2Ni powders to decrease from 74 to 1 ?m after activation and a 45-cycle test. After supplying sufficient hydrogen gas, the hoop strain on vessel wall was increased linearly with progressive cycles throughout the testing period. When the Mg2Ni alloy powders were agglomerated, the hoop strain increment was reduced. It indicates that the volume expansion induced by the Mg2Ni hydride powders was reduced by agglomeration.
43
Huang, Sih-ming, and 黃思銘. "Effects of Packing Fraction and Particle Size on the Expansive Deformation in the Reaction Vessel of Mg2Ni Alloy." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/8a6sg9.
Full textAbstract:
碩士國立中央大學
機械工程研究所
97
The purpose of this study is to investigate variations of the wall strain on the storage vessel of Mg2Ni alloy with different packing fractions and particle sizes during cyclic hydriding/dehydridng processes. A modification of hydride storage vessel with an internal gas tunnel is also investigated for its influence on the wall strain and hydrogen storage capacity. The reaction pressure conditions for the absorption and desorption steps were of 3 MPa and vacuum, respectively, at 255 oC. The particle morphology of the Mg2Ni alloy before activation and after a 50-cycle test was analyzed with scanning electron microscopy (SEM). Results showed that at a given position on the storage vessel surface, the hoop strain was increased with a higher packing fraction of alloy powders during the cyclic hydriding/dehydriding reactions. This resulted from a larger amount of pulverized fine powders generated by a larger packing fraction of alloy powders. Given a lower packing fraction, the hoop strain in the vessel wall induced by the hydriding/dehydriding reactions was increased with alloy powder size. For a higher packing fraction, a greater absorption strain was induced in the vessel packed with a larger initial powder size, while a greater desorption strain was present in the vessel packed with a smaller initial powder size. A greater extent of degradation of absorbed hydrogen content at the end of the 50-cycle test was observed for a smaller initial size of alloy powders as a result of formation of a larger agglomerated stack of alloy powders. A gas tunnel built at the center of the vessel was effective for enhancing the hydrogen storage capacity of the vessel and reducing the surface strain on the vessel wall. In summary, a larger initial powder size and an internal gas tunnel are favorable conditions for enhancing the hydrogen storage content of a metal-hydride reaction vessel.
44
Shen-DunLiang and 梁信惇. "The electrochemical properties of Mg2Ni hydrogen storage alloy with core-shell structure fabricated by mechanical alloying and chemical plating Ni." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/30005489409901059086.
Full text
45
Weng, Hao-Wei, and 翁浩偉. "A Study of Hydrogen Storage Performance for Mg2Ni Bed and Design of the Heat Exchange System for Metal-hydride Reactors." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/88842032246387081277.
Full textAbstract:
碩士國立臺灣海洋大學
機械與機電工程學系
95
The objective of this thesis is to investigate the performance of hydrogen absorption/desorption for a small metal hydride (MH) reactor. This is accomplished mainly by numerical simulation. The testing results are extracted from Wang [39]. The present work also intends to design the heat exchange system for a practical Mg2Ni reactor. In the aspect of numerical simulation for a MH reactor, a theoretical model developed by Sung and Deng [19] is used for calculating the variable effective conductivity of the Mg2Ni bed. This model is cast in the computer program for simulating the hydrogen absorption/desorption of the MH reactor. The results obtained are compared with previous numerical results [39] based on constant heat conductivity. The difference between them is generally small. It indicates that using a proper fixed value for the conductivity of the MH bed does not cause significant errors. Since the testing results [39] clearly show that the reaction rate for absorption/desorption decays as the number of reaction cycles increases. A simple mathematical model for describing the reaction rate constant is proposed. The model is in the form of an exponential function. The numerical results accounting for this effect match the experimental results more closely. This model can be applied to other metal hydrides. As for the design of the heat exchange system for a practical MH reactor, a double-pipe design is adopted. The inner pipe is filled with 4.5 kg MH powder. Cool or hot air flows in the annulus for cooling or heating the MH bed. A number of fins are added to the outer surface of the inner pipe for increasing the heat transfer area. Based on calculation, such design with fins needs low air speed (10 m/s and 12 m/s for hydrogen absorption/desorption, respectively) to satisfy the cooling/heating load for hydrogen absorption/desorption of the MH bed.
46
Hsu, Fu-kai, and 許傅凱. "Effects of alloying elements (Mn, Al) and ball milling treatment on the discharge capacity and cycle life of Mg2Ni-type hydrogen storage alloy." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/57667835867652760358.
Full textAbstract:
博士國立中央大學
機械工程研究所
100
Mg2Ni- x mol% Mg3MNi2 (M=Mn, Al；x=0, 15, 30, 60, 100), the novel composite alloys employed for hydrogen storage electrode, have been successfully synthesized by a method combining electric resistance melting with isothermal evaporation casting process (IECP). The characteristic of synthesizing the composite alloys Mg2Ni- x mol% Mg3MNi2 (M=Mn, Al) with various Mg3MnNi2 and Mg3AlNi2 content could be applied to both formation proportions of Mg3MnNi2 and Mg3AlNi2 through adding Mn and Al element, and Mg2Ni alloy synthesis through IECP. Therefore, the composite alloys Mg2Ni- x mol% Mg3MNi2 (M=Mn, Al；x=0, 15, 30, 60, 100) have been synthesized by the preparation method. The influences of the Mg3MnNi2 and Mg3AlNi2 phases on the structure, surface chemical composition and electrochemical properties of the synthesized materials were studied. To confirm the purity of the composite alloys, the composition and structure were examined by electron probe X-ray microanalyzer (EPMA) and X-ray diffraction (XRD). According to EPMA analysis, the composite alloys are composed of Mg2Ni phase and the new Mg3MnNi2 phase or the new Mg3AlNi2 phase. XRD analysis results show that both formation phases of the composite alloys were Mg2Ni with hexagonal crystal structure and Mg3MnNi2 or Mg3AlNi2 with face-centered cubic crystal structure. It is found on the electrochemical studies that maximum discharge capacities of the composite alloys increase with the increasing content of the Mg3MnNi2 and Mg3AlNi2 phase. The discharge capacities of the electrode alloys are effectively improved from 17 mAh/g of the Mg2Ni alloy to 166 mAh/g of the Mg3MnNi2 alloy and 110 mAh/g of the Mg3AlNi2 alloy, respectively. Cyclic voltammetry (CV) results confirm that the increasing content of the Mg3MnNi2 phase and the Mg3AlNi2 phase effectively improves the reaction activity of the electrode alloys. Surface analyses indicate that the phases can enhance the anti-corrosive performance of the particle surface of the composite alloys. It is also found on the cyclic discharge stability studies that both Mg3MnNi2 phase and Mg3AlNi2 phase possess a positive effect on the retardation of cycling capacity degradation rate of the electrode materials. Among the Mn-containing alloys, Mg3MnNi2 alloy had the best cyclic discharge stability. This alloy has kept 62.05% of its maximum discharge capacity at 15th cycle. It referred the improvement in the cycle life to that Mg3MnNi2 alloy was used to inhibit the formation of corrosive reaction against the alloy surface in the alkaline solution. Among the Al-containing alloys, Mg2Ni-15 mol% Mg3AlNi2 composite had the best anti-corrosion performance. This composite has kept 76% of its maximum discharge capacity (50 mAh/g) at 25th cycle. The improvement of the cycling stability of the electrode alloy with 15 mol% Mg3AlNi2 can be ascribed to the decrease in the rate of pulverization of the alloy during cycling, leading to retard the corrosion reaction against the alloy surface due to the formation of a dense Al2O3 film. The results as mention above reveal that Mg3MnNi2 phase possesses the advantage of improving discharge capacity and cyclic stability of the electrode alloy. In order to further enhance the electrochemical performance of Mg3MnNi2 alloy, the prepared Mg3MnNi2 alloy was ball milled with metallic Co and Ti element for 30 min to produce Mg3MnNi2- x mol% M (M=Co, Ti; x=0, 200) alloys. The influences of the Co and Ti element on the structure, surface corrosion behavior and electrochemical properties of the synthesized materials were investigated. For the ball milled Mg3MnNi2 alloy, the characteristic peaks of the Mg3MnNi2 phase decreased in intensity and broadened, revealing that there was a phase transformation from polycrystalline to nanocrystalline state. X-ray diffraction (XRD) studies showed that Co and Ti facilitated the amorphization of Mg3MnNi2 alloy. Furthermore, the addition of Co and Ti elements are effective in enhancing the anti-corrosion ability of the alloys. The maximum discharge capacities of ball-milled Mg3MnNi2, Mg3MnNi2-2Co and Mg3MnNi2-2Ti alloys were 206 mAh/g, 238 mAh/g and 209 mAh/g, respectively. Although Mg3MnNi2-2Ti alloy had lower maximum discharge capacity, the capacity retaining rate of this alloy was much higher than those of Mg3MnNi2 and Mg3MnNi2-2Co alloys. After ten cycles charge/discharge, the capacity retention rates for ball-milled Mg3MnNi2, Mg3MnNi2-2Co and Mg3MnNi2-2Ti alloys are 51%, 59% and 80%, respectively. These results indicate that the positive effect on suppressing of the oxidation of the Mg3MnNi2 alloy surface was caused by the introduction of Co and Ti metallic elements. Combined with XPS depth profile analyses, it is suggested that the TiO2 oxide layer would be effective in improving the cyclic stability of the electrode alloy. For improving the hydriding/dehydriding properties of Mg2Cu alloy through the substitution of Ni for Cu, few ones on the structure analyses of Mg-Cu-Ni ternary alloy were investigated. The effect of Ni-substitution on the structure and hydrogen storage properties of Mg2Cu1-xNix (x = 0, 0.2, 0.4, 0.6, 0.8, 1) alloys prepared by a method combining electric resistance melting with isothermal evaporation casting process (IECP) has been studied. The X-ray single-crystal diffraction results indicated that crystal structure transforms Mg2Cu with FCO into Ni-containing alloys with HCP structure, and it leads to a decrement of the cell volume with increasing Ni concentration. The Ni-substitution effects on the hydriding reaction indicated that absorption kinetics and hydrogen storage capacity increase in proportion to the concentration of the substitutional Ni. The activated Mg2Cu and Mg2Ni alloys absorbed 2.54 and 3.58 wt.% H, respectively, at 3000C under 50 atm H2. After a combined high temperature and pressure activation cycle, the charged samples were composed of MgH2, MgCu2 and Mg2NiH4 while the discharged samples contained ternary alloys of Mg-Cu-Ni system with the helpful effect of rising the desorption plateau pressures compared with binary Mg-Cu and Mg-Ni alloys. With increasing nickel content, the effect of Ni is actually effective in MgH2 and Mg2NiH4 destabilization, leading to a decrease of the desorption temperature of these two phases. The partial substitution of Cu for Ni is slightly effective in improving the discharge capacity of Mg-Cu-Ni alloys, and Mg2Ni0.6Cu0.4 alloy reaches the maximum discharge capacity (40 mAh/g) among the alloys.