Adolf Mikula

Effect of temperature on inter-metallic associations in Sb–Zn liquid alloys

Abstract A statistical mechanical theory, in conjunction with a compound formation model has been used to develop expressions for various thermodynamic and microscopic structural functions for 4:3 inter-metallic compounds. These expressions, in turn, have been used to investigate the alloying behaviour and its temperature dependence in Sb–Zn liquid alloys. Our expressions for 4:3 compounds not only reproduce the asymmetric nature of thermodynamic functions such as the excess free energy of mixing and the activity coefficient but also provide structural information about Sb–Zn liquid alloys. The study of concentration fluctuations in the long wavelength limit [Scc(0)], chemical short range order parameter ( α 1 ) and diffusion coefficient clearly demonstrate the presence of Zn 4 Sb 3 compounds in the melt. It is also observed that the tendency for inter-metallic associations, which leads to the formation of Zn 4 Sb 3 compounds, decreases with the increase of temperature.

Role of surface properties on the wettability of Sn–Pb–Bi solder alloys

Abstract A statistical mechanical model has been used to investigate the surface properties of Sn–Pb, Bi–Sn and Bi–Pb liquid alloys. Our study suggests a decrease in the surface tension of Sn–Pb alloys with increasing Pb component. In contrast, the addition of Pb atoms increases the surface tension of Bi–Pb liquid alloys. However, Bi atoms cause the lowering of the surface tension of Bi–Sn alloys. The Bi–Sn and Bi–Pb systems exhibit segregation of Bi atoms to the surface, whereas in the case of Sn–Pb alloys, there is evidence for the enrichment of the surface with Pb atoms. For all the systems, the degree of segregation increases with lowering of the temperature. Our results for binary systems have been extended to a ternary (Sn–Pb–Bi) system with the emphasis on the influence of the Bi component on the surface tension and surface segregation of conventional solder alloys i.e. Sn 0.6 Pb 0.4 . Our study suggests a lowering of the surface tension of Sn 0.6 Pb 0.4 alloys with the addition of Bi atoms. It is also observed that the surface of ternary alloys will be less enriched in Pb atoms in comparison with the conventional solder alloys, i.e. Sn 0.6 Pb 0.4 . The segregation of Bi atoms to the surface might inhibit the formation of a Pb layer near the intermetallic compound layer formed between Sn 0.6 Pb 0.4 alloys and the Cu substrate, as observed in de-wetted solder joints.

Calorimetric investigations of the two ternary systems Al-Sn-Zn and Ag-Sn-Zn

Abstract Using a Calvet type calorimeter, the enthalpy of mixing in the two ternary systems, Al–Sn–Zn and Ag–Sn–Zn was determined at 973 K. In the Al–Sn–Zn system, the investigations were carried out along three cross-sections with constant molar ratios of Sn: Zn = 1: 2, 1: 1 and 2: 1 and an aluminium content between 0 and 100 at.%. For the Ag–Sn–Zn system, the measurements have been done at constant molar ratios of Ag: Sn = 1: 3, 1: 1 and 3: 1 with zinc contents between 0 and 50 at.%. The substitutional solution model of Redlich–Kister according to the CALPHAD method was used for a least-square fit of the experimental data in order to get an analytical expression for the integral enthalpy of mixing. The ternary extrapolation models of Kohler, Muggianu, and Toop were applied on the binary data to compare measured, fitted, and extrapolated values.

Thermodynamic properties of liquid CuSnZn alloys

Abstract Using an appropriate galvanic cell, the partial free energies of zinc in liquid CuSnZn alloys were determined as a function of concentration and temperature. Thermodynamic properties were obtained for 40 alloys. Their composition was situated on four cross-sections with constant ratios Cu:Sn of 1:3, 1:2, 1:1 and 2:1. The integral free energy and the integral enthalpy for the ternary system at 1023 K were calculated by Gibbs-Duhem integration.

Effect of temperature on the surface properties of Cu-Sn liquid alloys

Abstract The concentration and temperature dependence of the surface tension and surface composition of Cu–Sn liquid alloys have been theoretically investigated with the application of statistical mechanical model based on layered structures. Our study suggests an increase in the surface tension ( σ ) with the increase of Cu concentration. Maximum increase in σ has been found around the compound forming concentration, i.e. Cu 0.75 Sn 0.25 . With regard to the effect of temperature on activity coefficient (γ), our study shows positive temperature coefficient at compound forming concentration, i.e. C Cu =0.75. The temperature buffering (d σ /d T =0) was found to occur around the equi-atomic composition. It may be inferred that positive temperature coefficient might be due to progressive dissociation at the surface of atomic clusters/associates/complexes associated with the γ-phase of the system. So far as surface segregation is concerned, the surface is quite enriched with Sn-atoms at all bulk concentrations. However, the extent of segregation decreases with the increase of the temperature.

Thermodynamic properties of liquid Bi–Sn alloys

Abstract The thermodynamic properties of liquid Bi–Sn alloys were measured over the whole composition range by an electromotive force (emf) method using a liquid electrolyte. The basic thermodynamic functions were calculated from the corresponding excess functions by using the Gibbs–Duhem integration at 723 K. The liquid Bi–Sn system was classified as a subregular solution and an asymmetrical curve of enthalpy of mixing vs. composition was found.

Comparison between calculated and measured thermodynamic data of liquid (Ag, Au, Cu)-Sn-Zn alloys ☆

Abstract The activity of zinc was measured in a series of liquid alloys in the three ternary systems, Ag-Sn-Zn [94Kar], Au-Sn-Zn [96Kar] and Cu-Sn-Zn [97Pen], with an emf (electromotive force) method. From these measurements and the slope of the emf vs. temperature (dE/dT) all thermodynamic properties were derived. The experimental values were compared with calculated results. For these calculations four different models were applied and the thermodynamic data of the binary systems, obtained from the literature, were used.

The Sn-In-Zn system-application of calphad technique to phase diagram measurement

The phase diagram of one promising lead-free solder system---the In-Sn-Zn system was well constructed by using accurate experimental methods in conjunction with CALPHAD technique. This work is a good example to show that the CALPHAD technique is very useful for phase diagram measurements, especially for those systems with a lot of experimental difficulties. The ternary interaction parameter of the Sn-In-Zn liquid phase was also calculated based on our experimental data and thermodynamic properties from the literatures.

Direct measurement of the concentration fluctuations in liquid Bi–Zn alloys

Abstract The e.m.f. method with a molten salt electrolyte was used to measure directly the composition gradient of the e.m.f. (i.e. (Δ E )/(Δ x )) and hence the concentration fluctuations of liquid Bi–Zn alloys above the miscibility gap are determined. The concentration fluctuations are strong and above the values of an ideal solution. In the region of miscibility gap the concentration fluctuations increase strongly with decreasing temperature and the flat maximum tends to be more steep towards the critical composition. A simple model assuming the existence of polyatomic self associates in a demixing liquid alloy is used to describe the concentration fluctuations. Further, Δ E vs temperature variation is used to infer the temperature and the composition of the binodal. The temperature dependence of the atomic transport properties, such as diffusion, is also discussed in relation to the concentration fluctuations.

Thermodynamic properties in the liquid Ag−Sb−Zn system

The change of the thermodynamic properties of the liquid binary Sb-Zn alloys with the addition of a third element, in this case silver, was determined. The thermodynamic properties of the liquid ternary Ag-Sb-Zn alloys were measured with an electromotive force (emf ) method at four cross sections with a constant Ag to Sb ratio of 3:1, 1:1, 1:3, and 1:9, respectively. At the first three cross sections, calorimetric measurements were also carried out to compare the integral enthalpy of mixing from direct measurements with the data of the emf measurements derived by Gibbs-Duhem integration.