The effect of solute atoms on the phase transformation kinetics of pure thallium

Abstract

Pure thallium exhibits β to α transformation on cooling at 508°K. The high temperature modification is face centered cubic structure in contrast to low temperature modification which is hexagonal close-packed structure. The thermodynamic properties and crystal structure of pure thallium have been determined by several investigators in the temperature range of 334°K to 773°K. In the present investigation, attempts have been made to determine the thermodynamic properties and phase transformation kinetics of pure thallium and the effect of solute atoms on the phase transformation characteristics and thermodynamic parameters of pure thallium. This study includes detailed investigations on the thermodynamic properties of the dilute Tl-Ag, Tl-Au, Tl-Zn, Tl-Cd, and Tl-Sn alloys in the thallium rich end. This investigation directly results in the determination of enthalpy,entropy, free energy, enthalpy of mixing, entropy of mixing and free energy of mixing for all alloy composition thereof. The enthalpy and temperature of phase transformation of pure thallium are considerably changed by the addition of solute atoms. The alloying elements belonging to the same group in the periodic table affect the phase transformation kinetics in a similar manner. However, the element having a higher atomic number in a group of element seems to make the most outstanding contribution. The free energy of mixing shows significant change due to the additions of solute atoms. This is due to the tendency of attractive interactions between unlike atoms. The conduction electrons from the solute atoms make important contributions to determine the nature of primary bonds.