The experimental study of the Bi–Sn, Bi–Zn and Bi–Sn–Zn systems

Abstract

The binary Bi-Sn was studied by means of SEM (Scanning Electron Microscopy)/EDS (Energy-Dispersive solid state Spectrometry), DTA (Differential Thermal Analysis)/DSC (Differential Scanning Calorimetry) and RT-XRD (Room Temperature X-Ray Diffraction) in order to clarify discrepancies concerning the Bi reported solubility in (Sn). It was found that (Sn) dissolves approximately 10 wt% of Bi at the eutectic temperature.The experimental effort for the Bi-Zn system was limited to the investigation of the discrepancies concerning the solubility limit of Zn in (Bi) and the solubility of Bi in (Zn). Results indicate that the solubility of both elements in the respective solid solution is approximately 0.3 wt% at 200 • C.Three different features were studied within the Bi-Sn-Zn system. Although there are enough data to establish the liquid miscibility gap occurring in the phase diagram of binary Bi-Zn, no data could be found for the ternary. Samples belonging to the isopleths with w(Bi) ∼ 10% and w(Sn) ∼ 5%, 13% and 19% were measured by DTA/DSC. The aim was to characterize the miscibility gap in the liquid phase. Samples belonging to the isopleths with w(Sn) ∼ 40%, 58%, 77/81% and w(Zn) ∼ 12% were also measured by DTA/DSC to complement the study of Bi-Sn-Zn. Solubilities in the solid terminal solutions were determined by SEM/EDS. Samples were also analyzed by RT-XRD and HT-XRD (High Temperature X-Ray Diffraction) confirming the DTA/DSC results for solid state phase equilibria.

Thermodynamic assessment of the Bi–Sn–Zn System

“…The calculations for the Zn-rich end of the phase diagram gave a negligible solubility of Bi in HCP Zn; less than 0.1 wt%. Experimental results [5] at 245 • C confirmed the low solubility of Zn in Rhombohedral A7 (Bi), as the sample with a Zn content of approximately 0.3 wt% clearly exhibits a two-phase structure. The solubility of both elements in the respective solid solution was found to be approximately 0.3 wt% at 200 • C. This value is in good agreement with the theoretical calculation for the solubility of Zn in Rhombohedral A7 (Bi), as the calculated solubility at 200 • C is 0.37 wt% of Zn.…”

“…However, discrepancies between experimental and calculated solubilities were found for Bi in HCP Zn, and particularly for the solubility of Bi in BCT A5 (Sn). The results given in [5] indicated a much lower solubility of Bi in the BCT A5 (Sn) solid solution (around 10 wt% at the eutectic temperature) and confirmed the need for a new thermodynamic description for the Bi-Sn system. This fact is especially important from the point of view of the development of the "COST531" thermodynamic database [2] because other important ternary system descriptions are based on this binary.…”

“…With respect to the different solubility of Bi in BCT A5 (Snrich) solid solution, we have utilized mainly the newly obtained phase equilibrium data from [5] for the reassessment of the system ( Fig. 2 shows these data superimposed on the phase diagram calculated using the thermodynamic parameters from the assessment of Ohtani and Ishida [10]).…”

“…An extensive experimental investigation of the Bi-Sn-Zn system has been conducted by Braga et al [5]. The solubilities of the components in the terminal solid solutions were measured and compared with predictions using thermodynamic parameters from [6] and [7].…”

“…This fact is especially important from the point of view of the development of the "COST531" thermodynamic database [2] because other important ternary system descriptions are based on this binary. Therefore, targeted experiments using scanning electron microscopy (SEM) + energy-dispersive solid-state spectrometry (EDS) and differential scanning calorimetry (DSC) were carried out in the Sn-rich part of the Bi-Sn phase diagram as part of the experimental study [5].…”