Design of a Nanometric AlTi Additive for MgB2-Based Reactive Hydride Composites with Superior Kinetic Properties

Solid-state hydride compounds are a promising option for efficient and safe hydrogen-storage systems. Lithium reactive hydride composite system 2LiBH4 + MgH2/2LiH + MgB2 (Li-RHC) has been widely investigated owing to its high theoretical hydrogen-storage capacity and low calculated reaction enthalpy (11.5 wt % H2 and 45.9 kJ/mol H2). In this paper, a thorough investigation into the effect of the formation of nano-TiAl alloys on the hydrogen-storage properties of Li-RHC is presented. The additive 3TiCl3·AlCl3 is used as the nanoparticle precursor. For the investigated temperatures and hydrogen pressures, the addition of ∼5 wt % 3TiCl3·AlCl3 leads to hydrogenation/dehydrogenation times of only 30 min and a reversible hydrogen-storage capacity of 9.5 wt %. The material containing 3TiCl3·AlCl3 possesses superior hydrogen-storage properties in terms of rates and a stable hydrogen capacity during several hydrogenation/dehydrogenation cycles. These enhancements are attributed to an in situ nanostructure and a hexagonal AlTi3 phase observed by high-resolution transmission electron microscopy. This phase acts in a 2-fold manner, first promoting the nucleation of MgB2 upon dehydrogenation and second suppressing the formation of Li2B12H12 upon hydrogenation/dehydrogenation cycling.Fil: Le, Thi-Thu. Helmholtz Zentrum Geesthacht; AlemaniaFil: Pistidda, Claudio. Helmholtz Zentrum Geesthacht; AlemaniaFil: Puszkiel, Julián Atilio. Helmholtz Zentrum Geesthacht; Alemania. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Castro Riglos, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Helmholtz Zentrum Geesthacht; Alemania. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Karimi, Fahim. Helmholtz Zentrum Geesthacht; AlemaniaFil: Skibsted, Jørgen. University Aarhus; DinamarcaFil: Gharibdoust, Seyedhosein Payandeh. University Aarhus; DinamarcaFil: Richter, Bo. University Aarhus; DinamarcaFil: Emmler, Thomas. Helmholtz Zentrum Geesthacht; AlemaniaFil: Milanese, Chiara. Università di Pavia; ItaliaFil: Santoru, Antonio. Helmholtz Zentrum Geesthacht; AlemaniaFil: Hoell, Armin. Helmholtz Zentrum Berlin für Materialien und Energie; AlemaniaFil: Krumrey, Michael. Physikalisch Technische Bundesanstalt; AlemaniaFil: Gericke, Eike. Universität zu Berlin; AlemaniaFil: Akiba, Etsuo. Kyushu University; JapónFil: Jensen, Torben R.. University Aarhus; DinamarcaFil: Klassen, Thomas. Helmholtz Zentrum Geesthacht; Alemania. Helmut Schmidt University; AlemaniaFil: Dornheim, Martin. Helmholtz Zentrum Geesthacht; Alemani

Contrast varied small-angle scattering on disordered materials using X-ray, neutron, and anomalous scattering

Schwerpunkt dieser Arbeit ist die Untersuchung der Struktur von Materialien und ihrer Entwicklung unter in situ Bedingungen. Dabei werden nanoskopische Strukturmotive in amorphen, ungeordneten und porösen Festkörpern mit Hilfe von Kleinwinkelstreuungstechniken identifiziert und quantifiziert. Es werden drei verschiedene wissenschaftliche Fragestellungen bezüglich drei unterschiedlicher Materialsystemen diskutiert. Erstens wird die Nanostruktur von Dichtefluktuationen in hydriertem amorphen Silizium (a-Si:H) charakterisiert. In den untersuchten a-Si:H Materialien wurden zwei unterschiedliche in die a-Si:H-Matrix eingebettete Phasen identifiziert und anhand ihrer Streuquerschnitte quantifiziert. Diese neuen Ergebnisse beantworten eine seit 20 Jahren ungelöste Fragestellung über das a Si:H Material. Zweitens wird die Adsorption, Kondensation und Desorption von Xenon (Xe) in den Poren einer mesoporösen Silizium (Si) Membran untersucht. Dabei werden Xe-spezifischen Charakterisierungsmethoden eingesetzt. Die neuen Ergebnisse führen zu einem detaillierten Verständnis der Physisorption von Xe in porösem Silizium und zeigen deutliche Unterschiede zwischen Porenfüllungs- und Porenentleerungsmechanismen auf. Zuletzt wird die natürliche Alterung (NA) einer Aluminium-Magnesium-Silizium-Modelllegierung diskutiert. Die Streuexperimente weisen auf das Vorhandensein von Segregationszonen hin und unterstützen die Interpretation dieser Zonen als MgSi-Nanophasen in der Al-Matrix.The investigation of material structures and their evolution under in situ conditions is the main focus of this work. Thereby, nanostructural motives in amorphous, disordered, and porous solids are identified and quantified using small-angle scattering techniques. Three different scientific questions concerning three different material systems are discussed. First, the nanostructure of density fluctuations in hydrogenated amorphous silicon (a-Si:H) is evaluated and quantified. Second, the adsorption, condensation, and desorption of xenon (Xe) confined in the pores of a mesoporous silicon (Si) membrane is studied in situ using Xe-specific characterization methods. Finally, the natural aging (NA) of an aluminum-magnesium-silicon model alloy (Al-0.6Mg-0.8Si) is discussed

Exploring the hidden world of solute atoms, clusters and vacancies in aluminium alloys

Precipitation hardening involves solutionising, quenching and annealing steps, the latter often at various temperatures. The phenomena observed in Al-Mg-Si alloys are very complicated and partially not well understood. During and after quenching, solute atoms diffuse through the lattice assisted by vacancies and form atom clusters that gradually grow. These act back onto vacancies, which complicates the situation. We apply positron annihilation techniques in addition to traditional hardness, resistivity and thermal measurements to clarify what happens in various stages of thermal treatment: The quenching process can be divided into a stage of vacancy loss and of precipitation. Very short artificial ageing treatments after heating at different rates show that there is a competition between vacancy losses and cluster formation as the temperature increases. The difference between natural ageing and artificial ageing can be defined based on the importance of excess vacancies. Based on such results the behaviour of “invisible” objects such as vacancies and small clusters can be better understood but some open question remain such as the kinetics of secondary ageing or the details of the negative effect of natural ageing on artificial ageing

Exploring the hidden world of solute atoms, clusters and vacancies in aluminium alloys

Precipitation hardening involves solutionising, quenching and annealing steps, the latter often at various temperatures. The phenomena observed in Al Mg Si alloys are very complicated and partially not well understood. During and after quenching, solute atoms diffuse through the lattice assisted by vacancies and form atom clusters that gradually grow. These act back onto vacancies, which complicates the situation. We apply positron annihilation techniques in addition to traditional hardness, resistivity and thermal measurements to clarify what happens in various stages of thermal treatment The quenching process can be divided into a stage of vacancy loss and of precipitation. Very short artificial ageing treatments after heating at different rates show that there is a competition between vacancy losses and cluster formation as the temperature increases. The difference between natural ageing and artificial ageing can be defined based on the importance of excess vacancies. Based on such results the behaviour of invisible objects such as vacancies and small clusters can be better understood but some open question remain such as the kinetics of secondary ageing or the details of the negative effect of natural ageing on artificial agein

Design of a Nanometric AlTi Additive for MgB₂‑Based Reactive Hydride Composites with Superior Kinetic Properties

Solid-state hydride compounds are a promising option for efficient and safe hydrogen-storage systems. Lithium reactive hydride composite system 2LiBH₄ + MgH₂/2LiH + MgB₂ (Li-RHC) has been widely investigated owing to its high theoretical hydrogen-storage capacity and low calculated reaction enthalpy (11.5 wt % H₂ and 45.9 kJ/mol H₂). In this paper, a thorough investigation into the effect of the formation of nano-TiAl alloys on the hydrogen-storage properties of Li-RHC is presented. The additive 3TiCl₃·AlCl₃ is used as the nanoparticle precursor. For the investigated temperatures and hydrogen pressures, the addition of ∼5 wt % 3TiCl₃·AlCl₃ leads to hydrogenation/dehydrogenation times of only 30 min and a reversible hydrogen-storage capacity of 9.5 wt %. The material containing 3TiCl₃·AlCl₃ possesses superior hydrogen-storage properties in terms of rates and a stable hydrogen capacity during several hydrogenation/dehydrogenation cycles. These enhancements are attributed to an in situ nanostructure and a hexagonal AlTi₃ phase observed by high-resolution transmission electron microscopy. This phase acts in a 2-fold manner, first promoting the nucleation of MgB₂ upon dehydrogenation and second suppressing the formation of Li₂B₁₂H₁₂ upon hydrogenation/dehydrogenation cycling