A. Yakymovych

Enthalpy Effect of Adding Cobalt to Liquid Sn-3.8Ag-0.7Cu Lead-Free Solder Alloy: Difference between Bulk and Nanosized Cobalt

Heat effects for the addition of Co in bulk and nanosized forms into the liquid Sn-3.8Ag-0.7Cu alloy were studied using drop calorimetry at four temperatures between 673 and 1173 K. Significant differences in the heat effects between nano and bulk Co additions were observed. The considerably more exothermic values of the measured enthalpy for nano Co additions are connected with the loss of the surface enthalpy of the nanoparticles due to the elimination of the surface of the nanoparticles upon their dissolution in the liquid alloy. This effect is shown to be independent of the calorimeter temperature (it depends only on the dropping temperature through the temperature dependence of the surface energy of the nanoparticles). Integral and partial enthalpies of mixing for Co in the liquid SAC-alloy were evaluated from the experimental data.

Viscosity of liquid Co–Sn alloys: thermodynamic evaluation and experiment

Shear viscosity measurements were performed for liquid Co–Sn alloys over a wide temperature range above the respective liquidus temperatures. A high temperature oscillating-cup viscometer was used. It was found experimentally that viscosity as a function of temperature obeys an Arrhenius law. The data were compared with calculated values, obtained from different thermodynamic approaches. A good agreement was found between experimental results and calculated ones by the Budai–Benkö–Kaptay model.

Viscosity of Sb-Sn Melts

The viscosity of Sb-Sn melts containing 0, 5, 10, and 20 at % antimony has been measured as a function of temperature by the oscillating cylinder method. The composition and temperature dependences of the viscosity coefficient deviate from classical theory predictions. The anomalous behavior is interpreted in terms of melt structure and changes in short-range order. Structural changes in the Sb-Sn melts are assumed to lead to an anomalous increase in viscosity coefficient.

Sn-Ag-Cu Nanosolders: Solder Joints Integrity and Strength

Although considerable research has been dedicated to the synthesis and characterization of lead-free nanoparticle solder alloys, only very little has been reported on the reliability of the respective joints. In fact, the merit of nanoparticle solders with depressed melting temperatures close to the Sn-Pb eutectic temperature has always been challenged when compared with conventional solder joints, especially in terms of inferior solderability due to the oxide shell commonly present on the nanoparticles, as well as due to compatibility problems with common fluxing agents. Correspondingly, in the current study, Sn-Ag-Cu (SAC) nanoparticle alloys were combined with a proper fluxing vehicle to produce prototype nanosolder pastes. The reliability of the solder joints was successively investigated by means of electron microscopy and mechanical tests. As a result, the optimized condition for employing nanoparticles as a competent nanopaste and a novel procedure for surface treatment of the SAC nanoparticles to diminish the oxide shell prior to soldering are being proposed.

Determination of Liquidus Temperature in Sn–Ti–Zr Alloys by Viscosity, Electrical Conductivity and XRD Measurements

Abstract The Sn – Ti – Zr system is an important subsystem for Cu based active brazing filler metals. Experimental results on this system, however, are rather scarce. The diagram is rather uncertain regarding most of the liquidus, especially on the Sn rich side. In this work, the atomic structure and temperature dependence of structure-sensitive physical properties (dynamic viscosity and electrical conductivity) of liquid Sn – Ti – Zr alloys in the Sn-rich corner were investigated in a wide temperature range with special attention to the melting – solidification region. The results allowed the liquidus line position to be specified.

Liquid Co–Sn alloys at high temperatures: structure and physical properties

ABSTRACT The Co–Sn system is an important subsystem for Sn-based anode materials of lithium-ion batteries. Experimental results on the physical–chemical properties of this system in the liquid state, however, are rather sparse. In this work, the atomic structure and structure-sensitive thermophysical properties (viscosity, electrical resistivity, and thermoelectric power) of liquid Co–Sn alloys were investigated in a wide temperature range with special attention to the melting-solidification region. The obtained experimental results were combined with differential thermal analysis (DTA) data in order to verify the liquidus curve in the Sn-rich part of the Co–Sn phase diagram.

The structure and viscosity features in In–Bi near-eutectic melts

The In1− x Bi x (x = 0.40, 0.34, 0.23, 0.13, 0.09) molten alloys have been studied by means of viscosity measurements and X-ray diffraction method. Temperature dependence of viscosity coefficient shows the Arrhenius like behavior with anomalous in form of local maximum and significant scattering of experimental values. The features in temperature dependencies of viscosity coefficient were studied also by means of X-ray diffraction method.

Electrical conductivity and thermoelectric power of liquid Co–Sn alloys

The electrical conductivity and thermoelectric power of liquid Co–Sn alloys were investigated in a wide concentration and temperature range. It was shown that the electrical conductivity of the melts decreased with an increase of the Co content. The results are interpreted in the context of the s–d hybridisation model. The corresponding behaviour is caused by sharing electrons from one metal to another one. This is in agreement with the concept of Fermi enthalpy, according to which up to two electrons from Sn transfer to the uppermost bands of Co.

Thermophysical Properties of Liquid Silver-Bismuth-Tin Alloys

Tin-bismuth-silver alloys are under intense consideration as favorable lead-free solders for consumer electronics and telecommunications. The investigated samples of Ag-Bi10-Sn with Ag content from 3.33 to 10 at.% were prepared both in the traditional bulk form and in the ribbon form by the rapid solidification technique. The electrical conductivity and thermal conductivity, thermoelectric power and viscosity studies were carried out in a wide temperature range above the liquidus. Corresponding fit relations have been derived.

AlCoCrCuFeNi-Based High-Entropy Alloys: Correlation Between Molar Density and Enthalpy of Mixing in the Liquid State

The density of the liquid equiatomic high-entropy alloys, namely, AlCoCrCuFeNi, AlCoCuFeNi, and CrCoCuFeNi, as well as quaternary alloys AlCoCuFe and AlCoCrNi was determined over a wide temperature range. The measurements were performed by a non-contact technique combining electromagnetic levitation and optical dilatometry. The temperature and composition dependencies of the density were analyzed and the molar excess volumes were calculated. The integral enthalpy of mixing of multi-component alloys was predicted using extended Kohler’s model, while Miedema’s model was used for binary sub-system alloys. It has been found that a negative excess volume of the investigated Al-containing liquid alloys correlates with a negative enthalpy of mixing. In contrast, a positive excess volume and an endothermic reaction have been estimated for the liquid CoCrCuFeNi alloy. The change of the excess volume in the Al-containing liquid alloys is affected by two basic effects, namely, compression of the Al matrix and formation of compounds in the melt.