1,720,998 research outputs found
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
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
Viscosity of liquid Ag-Cu alloys and the competition between kinetics and thermodynamics
No full text
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
Synthesis and thermodynamics of Ag–Cu nanoparticles
No full textMetallic silver, copper, and Ag-Cu nanoparticles (NPs) have been produced by a chemical reduction method. The obtained nanoparticles were characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). A side-segregated configuration was observed for the one-pot synthesized Ag-Cu NPs, and the melting temperature depression of about 14 degrees C was found by differential scanning calorimetry (DSC). A comparison between the new experimental data, the literature data on Ag-Cu bimetallic NPs and the corresponding theoretical values obtained from the Ag-Cu nano-sized phase diagram was done, whereas the melting behaviour of Ag and Cu metal nanoparticles was discussed in the framework of the liquid layer model (LLM)
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
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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