The analytical description of excess functions was made possible using more advanced treatment of experimental data with respect to literature.

Keywords:Knudsen effusion mass spectrometry Redlich-Kister-Muggianu model Activity Excess Gibbs energy Ternary and binary L-parameter a b s t r a c tThe vaporisation of a liquid Al-Cu-Sn system has been investigated at 1273-1473 K by Knudsen effusion mass spectrometry (KEMS) and the data fitted to a Redlich-Kister-Muggianu (RKM) sub-regular solution model. Thirty-one different compositions (41 samples) have been examined at eight fixed copper mole fractions, X Cu = 0.10, 0.20, 0.30, 0.333, 0.40, 0.50, 0.60 and 0.70. The ternary L-parameters, the thermodynamic activities and the thermodynamic functions of mixing have been evaluated using standard KEMS procedures. In addition, the same quantities were obtained from the measured ion intensity ratios of Al + to Cu + , Al + to Sn + and Cu + to Sn + using a mathematical regression technique. The intermediate data obtained directly are the RKM ternary L-parameters that are, as a function of temperature, as follows:(0) = (14270 ± 1270) + (100.1 ± 7.6)T − (11.77 ± 0.93)T ln(T ); L (1) = (145600 ± 9780) + (101.6 ± 58.7)T − (15.56 ± 7.14)T ln(T ); L (2) = (76730 ± 1240) + (79.2 ± 7.4)T − (15.69 ± 0.91)T ln(T ).From the obtained ternary L-parameters the integral molar excess Gibbs energy, the excess chemical potentials, the activity coefficients and the activities have been evaluated. Using the temperature dependence of the activities, the integral and partial molar excess enthalpies and entropies can be also determined. In addition, for comparison, for some compositions, the Knudsen effusion isothermal evaporation method (IEM) and the Gibbs-Duhem ion intensity ratio method (GD-IIR) were used to determine activities and good agreement was obtained from the RKM model.

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La,Sr)(Co,Fe)O 3-d is very common as cathode material in SOFC applications. Sr in this type of cathode material is very reactive to form secondary phases with other oxides, which affect micro-structures and properties of the cathode materials, GDC layers and ZrO 2 -based electrolytes. The Sr-related degradation issues, Cr poisoning and volatile Sr species formation, are studied. As supplement to existing experimental knowledge on Cr poisoning, specific thermodynamic aspects for Cr poisoning are discussed. The thermodynamic calculations show that the partial pressure pCrO 3 has a stronger temperature dependence than pCrO 2 (OH) 2 , and when considering the reaction between SrO and CrO 3 (g), dependent on different pCrO 3 and pO 2 , different Sr-Cr-O compounds SrCrO 4 , SrCrO 3 , Sr 3 Cr 2 O 8 or Sr 2 CrO 4 could be formed. In addition, thermodynamic calculations show that in the presence of water vapor, formation of volatile Sr(OH) 2 is possible as well. pSr(OH) 2 depends on temperature, pH 2 O and SrO activity and can be of the same order of magnitude as pCrO 2 (OH) 2 . Volatile Sr(OH) 2 can diffuse through the porous GDC layer and react with ZrO 2 -based electrolytes to form SrZrO 3 precipitates. The reaction between gaseous Sr species and 8YSZ sheet is studied experimentally. The surface of the 8YSZ sheet is investigated by SEM coupled with EDS, confirming the deposition of Sr. K E Y W O R D S degradation, solid oxide fuel cell, thermodynamics

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