Studies on thermodynamics of As-Sn liquid solution

The activity of arsenic in liquid phase in the system As-Sn was studied by means of the isopiestic technique. The all-silica vertical cell sealed unde r vacuum was used in which two zones of temperature were maintained during the experiment. The arsenic vapour pressure in the system was set by solid arsenic in lower temperature zone, which temperature was varied in the rang e 585 - 790 K. The liquid As-Sn alloy was kept at the temperature 1173 - 13 73 K. The equilibrium arsenic concentration in the alloy was determined fro m the mass balance. Next, the activities of arsenic in liquid solution refe rred to the pure liquid as a standard were calculated from the partial pres sures of four arsenic species present in gas phase and the free energy chan ge on melting. The experimental results regarding the excess free energy of liquid solution were fitted to the Redlich-Kister formula with three param eters. The activities of both components of liquid solutions determined in the present work axe low i.e. the solution shows strong negative deviation from ideal behaviour. These results agree well with these of Kaczmarczyk an d Sukiennik, obtained by means of static method. However, two earlier publi cations suggested much weaker negative deviation from ideal behaviour.