Thermodynamic property of tellurium in molten iron measured by the transpiration method

Abstract

Tellurium is an important alloying element in free-machining steel, but its thermodynamic properties in molten iron are not well understood. In the present study, the standard Gibbs energy (ΔG°) for the dissolution of tellurium gas into molten iron was determined in the temperature (T) range from 1 823 to 1 873 K by a vapor-liquid equilibration technique, in which the transpiration method was used to control the vapor pressure of tellurium. This relationship is expressed by the following equations: Te(g)=Te(1mass% in Fe) ΔG° = (-147 000±6 000)+(53.6±3.2)T J/mol. We quantitatively confirmed that tellurium is thermodynamically less stable than oxygen or sulfur in molten iron. We also found a correlation between the standard Gibbs energy for the dissolution of chalcogens into molten iron and the standard Gibbs energy for the formation of the respective iron-chalcogenides.