Experimental Determination of the Activities of Liquid Bi-Sn Alloys

The paper addresses the measurement of the partial molar Gibbs energy ( $$\Delta {\stackrel{-}{G}}_{Bi},\Delta {\stackrel{-}{G}}_{Sn}$$ ), thermodynamic activity ( $${a}_{Bi},{a}_{Sn}$$ ) and the activity coefficient ( $${\gamma }_{Bi ,}{\gamma }_{Sn}$$ ) of the Bi-Sn binary system at 600 and 903 K. The experiments were carried out in an H-shaped electrochemical cell based on the measurement of electromotive force with the reversible electrode–solid electrolyte. The measuring electrode was made of Bix-Sn1−x alloys with x ranging from 0.1 to 0.9, step 0.1. The reference electrode was manufactured from pure bismuth, while the electrolyte was a mixture of 17% moles KCl and 83% moles SnCl2 (selected because it contains free ions Sn and the melting temperature of the electrolyte (563 K). To obtain reliable experimental data, each measurement was repeated five times and the standard deviation/error was calculated. Based on error propagation law, the mathematical expression of the compound uncertainty for each quantity addressed in the paper was derived. An innovative derivation is presented for the compound uncertainty (uc) of γSn. The values of the $$\Delta {\stackrel{-}{G}}_{Bi},\Delta {\stackrel{-}{G}}_{Sn}$$ , aBi, aSn, γBi and γSn are accompanied by their expanded uncertainty having a 95% confidence level. The novelties addressed in the paper are the values of ΔGBi, ΔGSn, aBi, aSn, γBi and γSn in the Bi-Sn binary system at 600 and 903 K.