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Experimental Thermodynamics and Surface Properties of Ag-Cu-Ge Solder/Braze Alloys
No full textAg-based alloys have industrial importance in relation to their use as high-temperature solders in jewellery or braze alloys for thermoelectric modules. Good wetting properties and a tarnish-resistance of Ag-Ge and Ag-Cu-Ge alloys together with appropriate mechanical properties make them good candidates for bonding sterling silver (Ag-7.5Cu, in wt.%). The melting temperature and the heat of melting of Ag-Cu, Ag-Ge and Ag-Cu-Ge eutectic alloys have been measured by differential scanning calorimetry. From a technological point of view, particular attention should be paid to the surface tension, a key property of the joining processes. The aim of this study is to correlate the thermodynamic properties of the Ag-Cu-Ge system and its subsystems with their surface properties and to compare the model predicted property values to the data available in the literature
Wetting and interfacial reactions: Experimental study of the Sb-Sn-X (X = Cu, Ni) systems
No full textExperimental studies of the Cu-Sb-Sn and Ni-Sb-Sn systems have been carried out by the wetting tests, followed by the analysis of the microstructural evolution occurring at the interface between the liquid alloy and solid substrate. The wetting experiments on the Sb30Sn70 / (Cu, Ni) and Sb38.4Sn61.6 / (Cu, Ni) systems have been performed by using a sessile drop apparatus. The wetting behaviour of the two alloys in contact with Cu-substrate differs from that observed in the case of Ni-substrate. The Sb-Sn alloy / substrate interface was characterised by SEM-EDS analyses. For each system, the solidliquid interactions and the phases formed at the interface were studied with the help of the corresponding phase diagrams
CORROSION PERFORMANCES OF Al-Ni AND Al-Ni COMPOSITE COATINGS ON CARBON STEEL IN A SALINE ENVIRONMENT
No full textThe corrosion behaviour of three coating types (Al-Ni, 70 wt. % Al-Ni / 30 wt. % Al2O3 and 30 wt. % Al-Ni / 70 wt. % Al2O3) applied by plasma spray technique on carbon steel specimens has been studied in 3.5% sodium chloride solution. The coated specimens were tested under corrosion-only and wear-corrosion conditions and the extent of the corrosion attack was assessed by electrochemical techniques and observations by optical (OM) and scanning electron (SEM) microscopes.
The presence of the intermetallic alloys AlNi3 and AlNi (in traces) was detected in the coatings by X-Ray Diffraction (XRD) analysis. Therefore, tests were also carried out on massive AlNi3 and AlNi specimens (prepared by fusion of stoichiometric amounts of the elements) and the results were compared to those obtained from the coatings themselves, sprayed on glass and from the coated steel specimens.
It was found that the coatings suffered from active corrosion while the intermetallic alloys were noble passive materials, likely because the spraying process induced the solidification of a high fraction of random amorphous Al-Ni solid solution (undetectable by XRD) in the coatings, while only a limited amount of ordered intermetallic alloys was present.
Short circuiting tests and SEM-Energy Dispersion X-Ray (SEM-EDX) analysis showed that the substrate was galvanically protected by the coatings themselves, particularly when they contained a high Al-Ni phase fraction
Surface and transport properties of liquid Ag–Sn alloys and a case study of Ag–Sn eutectic solder
No full textThis review represents the state of the art in the thermophysical properties of liquid Ag-Sn alloys highlighting the surface and wetting properties of Ag-Sn eutectic solder. It includes an atomistic approach developed within the framework of statistical mechanical theory in conjunction with a Quasi Lattice Theory that, through a rigorous mathematical formalism, provides exact relationships between the properties in terms of classical thermodynamics. The model predicted property values are substantiated by available experimental data. Based on the phase diagram evidence about the existence of epsilon-Ag3Sn intermetallic compound, the surface (surface tension and surface composition), transport (viscosity and diffusivity) properties and microscopic functions (concentration fluctuations in the long-wavelength limit and chemical short-range order parameter) have been studied using the Compound Formation Model in a weak interaction approximation and Quasi Chemical Approximation for regular solutions. A case study of Ag-Sn eutectic alloy is presented. Taking into account its importance for design and development of lead free solder alternatives, the literature data on the wettability and the phases formed at the interface between Ag-Sn eutectic alloy and different substrates (Cu, Ni, Au, Pd) have also been analysed
Phase Relations of the Sm–Ni–Al Ternary System at 800 °C in the 30–100 at.% Al Region
No full textThe Sm–Ni–Al phase relationships at 800 °C have been investigated by using several well–focused experimental techniques such as X–Ray Powder Diffraction (XRPD), Light Optical Microscopy (LOM) and Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Microprobe Analysis (EPMA). The isothermal section of the Sm–Ni–Al system at 800 °C was constructed according to the present experimental results. More than 50 alloys have been synthesized and characterized in the 30–100 at.% Al region. At 800 °C, 9 intermetallic phases have been confirmed, characterized and their relationships have been established. In the Al-rich corner, the presence of two ternary invariant reactions have been postulated whilst along the 16.67 at.% Sm isopleth, the presence of two structurally related extended solid solutions have been observed. The determined phase equilibria at 800 °C are discussed and compared with the isothermal section at 500 °C already reported in literature
New Insights into Phase Equilibria of the Sb-Sn System
No full textA new experimental investigation of the Sb-Sn phase diagram has been performed. Special attention was focused on the phase equilibria within SbSn-Sb3Sn4 composition range. Phase equilibria have been investigated by DSC measurements combined with a thorough optical and electronic microscopy examination with a special attention to the SbSn-Sb3Sn4 phase transformation. Both DSC and metallographic results have been critically evaluated and debated. The presence of two peritectic reactions L + Sb3Sn4 ⇌ (βSn) at 243 ± 1 °C and L + (Sb) ⇌ (SbSn) at 420 ± 1 °C have been confirmed. The invariant reaction at 321 ± 1 °C has been observed and an additional small effect at about 330-340 °C was systematically recorded. These results have been extensively discussed
Influence of noble metals alloying additions on the corrosion behaviour of titanium in a fluoride-containing environment
No full textTitanium alloys exhibit excellent corrosion resistance in most aqueous media due to the formation of a stable oxide film, and some of these alloys (particularly Ti-6Al-7Nb) have been chosen for surgical and odontological implants for their resistance and biocompatibility. Treatment with fluorides (F-) is known to be the main method for preventing plaque formation and dental caries. Toothpastes, mouthwashes, and prophylactic gels can contain from 200 to 20,000 ppm F- and can affect the corrosion behaviour of titanium alloy devices present in the oral cavity. In this work, the electrochemical corrosion behaviour of Ti-1M alloys (M = Ag, Au, Pd, Pt) was assessed in artificial saliva of pH = 3.0 containing 910 ppm F- (0.05 M NaF) through open circuit potential, E-OC, and electrochemical impedance spectroscopy (EIS) measurements. The corrosion behaviour of the Ti-6Al-7Nb commercial alloy was also evaluated for comparison
Electrocatalytic activity of crystalline Ni-Co-M (M = Cr, Mn, Cu) alloys on the oxygen evolution reaction in an alkaline environment
No full textTernary Ni60Co30M10 (M 1⁄4 Cr, Mn, Cu) crystalline alloys have been characterized by means of microstructural and electrochemical techniques in view of their possible applications as electrocatalytic materials for oxygen evolution reaction (OER). The electrochemical efficiency of the electrodes has been studied on the basis of electrochemical data obtained from steady-state polarization and electrochemical impedance spectroscopy (EIS) techniques in 1 M NaOH solution at 298 K. The results were compared with those obtained on a Ni60Co40 commercial alloy. The overall experimental data indicate that alloying Ni-Co with Cr, Mn and Cu leads to an increase of electrocatalytic activity in oxygen evolution with respect to the Ni-Co alloy. High catalytic efficiencies were achieved on Ni60Co30Mn10 and Ni60Co30Cr10 electrodes, the latter being the best electrocatalyst for the OE
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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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