6,259 research outputs found
MATGEN-IV.3 - third summer school on Materials for Generation IV reactors: Fundamentals, ongoing research and open questions
No full textThe MATGEN IV.3 summer school focuses on structural materials for Generation IV nuclear reactors, one of the prominent solutions that could satisfy the increasing demands for cost-effective energy, sustainable development and environmental constraints in the context of global climate change. Fundamental research in materials science, associated with efforts for the industrial development of innovating materials, are key issues for the successful implementation of systems such as Generation IV nuclear reactors. Indeed, nowadays, no structural materials in use meet satisfactorily the specifications and performances imposed by the design of such systems, for the requirements are severe for microstructural stability, mechanical behavior and corrosion resistance under irradiation and high temperatures. Moreover, since two or three decades is the typical time scale for developing and preparing industrially new materials, the conclusion is reached that research should be made now for anticipating the needs of tomorrow for generation IV structural materials. Inline with the above, MATGEN-IV summer schools aim at improving basic understanding of the phenomena controlling the properties of materials, thus opening the way for the development of innovating structural materials for nuclear applications. Extended references to key experiments and multi-scale-modelling will be combined within a recursive procedure relying on the Advanced Materials Design Method with target the design and selection of materials
14th Workshop on "Multiscale Modelling of Fe-Cr Alloys for Nuclear Applications" & GetMat/WP4 Technical Meeting
No full textWe review the experimental evidence of the non-monotonic behaviour of FeCr alloys versus Cr content,particularly under irradiation (ordering versus segregation tendencies, microstructure and phase evolution,hardening and embrittlement), together with the theoretical efforts done at the electronic and atomic level to interpret them. We summarize the achievements of the two interatomic potentials developed for this system and perform a careful scrutiny of their limitations. We emphasise the difficulties related to the study, at the atomic-level, of concentrated alloys and propose routes to overcome them. Finally, we advance some opinions regarding the crucial points that deserve further investigation in order to fully understand this important binary alloy, at the basis of the steels for current and future nuclear applications
Synthesis, characterization and thermal stability of SnAg and SnAgCu nanoparticles
No full textThe melting temperature and melting enthalpy of SnAg and SnAgCu (SAC) nanocrystals with diameters of approximately 30 nm was determined and, by means of Differential Scanning Calorimetry (DSC) a depression melting temperature of 7–10 °C was observed for both systems. The new experimental results were compared to the predicted values as well as available datasets. X-ray diffraction (XRD) analysis was performed to characterize the as-prepared and heat treated samples. Scanning electron microscopy (SEM and FE-SEM) analysis was carried out to study the morphology, microstructure and phase evolution of the as-synthesized particles before and after the heating process
Experimental thermodynamics, surface and transport properties of liquid Ag-Ge alloys
No full textThe aim of this study is to correlate the thermodynamics of liquid Ag-Ge alloys with their thermophysical properties such as the surface tension, viscosity, electrical resistivity and microscopic functions. For this purpose the Quasi-Chemical Approximation (QCA) for the regular solution and Faber-Ziman theory have been applied to describe the mixing behaviour of Ag-Ge melts in terms of the energetics and structure. Concerning the Ag-Ge system, the most important is Ag-24.5Ge (in at %) eutectic alloy, widely used as a brazing filler material. The melting temperature and the heat of melting of Ag-Ge eutectic alloy were measured by Differential Scanning Calorimetry (DSC). From a technological point of view, particular attention should be paid to the surface tension, a key property of the joining processes. Accordingly, the QCA and Butler’s model calculations have been done and subsequently, the model predicted values were compared to available literature data
Effects of Sb addition on the properties of Sn-Ag-Cu/(Cu, Ni) solder systems
No full textThe wetting characteristics and microhardness of the Sn-Ag-Cu (SAC) near eutectic alloy and the effects of a small addition of antimony on these properties have been investigated. The contact angle measurements on the two Sn-rich alloys, i.e. the Sn-1.8Ag-0.7Cu and Sn-1.9Ag-0.4Cu-2.1Sb (in wt %) in contact with Cu and Ni substrates have been performed by using a sessile drop apparatus. Although the two solders investigated exhibit different spreading kinetics on Cu and Ni substrates, their final contact angle values indicate a good wetting of these alloys on both substrates. The melting behaviour of two SAC type alloys and the interfaces between these solders and substrates have been characterised by DSC and SEM/EDS analyses, respectively. The results obtained were explained qualitatively by means of the corresponding phase diagrams. The microhardness of SAC solders investigated slightly increases with Sb addition
Design of Ag-Ge-Zn braze/solder alloys: Experimental thermodynamics and surface properties
No full textThe experimental investigation of the Ag-Ge-Zn phase diagram was performed by
using combined microstructural and Differential Scanning Calorimeter (DSC)
analyses. The samples were subjected to thermal cycles by a heat-flux DSC
apparatus with heating and cooling rate of 0.5 or 0.3°C/min. The
microstructure of the samples, both after annealing and after DSC analysis,
was studied by optical and scanning electron microscopy coupled with EDS
(Energy Dispersive Spectroscopy) analysis. Considering the slow heating and
cooling rate adopted, the isothermal section at room temperature was
established. No ternary compounds were observed. On the basis of the
experimental investigations the invariant reactions were identified.
Combining the thermodynamic data on the Ag-Ge, Ag-Zn and Ge-Zn liquid phases
by means of Butler’s model the surface tension of Ag-Ge-Zn alloys was
calculated
Chemical ordering in magic-size Ag-Pd nanoparticles
No full textChemical ordering in magic-size Ag-Pd nanoalloys is studied by means of global optimization searches within an atomistic potential developed on the basis of density functional theory calculations. Ag-rich, intermediate and Pd-rich compositions are considered for fcc truncated octahedral, icosahedral and decahedral geometric structures. Besides a surface enrichment in Ag, we find a significant subsurface enrichment in Pd, which persists to quite high temperatures as verified by Monte Carlo simulations. This subsurface Pd enrichment is stronger in nanoparticles than in bulk systems and is rationalized in terms of the energetics of the inclusion of a single Pd impurity in an Ag host nanoparticle. Our results can be relevant to the understanding of the catalytic activity of Ag-Pd nanoparticles in those reactions in which subsurface sites play a role. This journal is © the Owner Societies 2014
Viscosity of liquid Ag-Cu alloys and the competition between kinetics and thermodynamics
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