Thermodynamic Significance of Heat of Transport in Interstitial Solid Solutions

Abstract

The theoretical relationships involved in thermal diffusion have been re‐examined. It has been shown from strictly thermodynamic considerations that in dilute solid solutions the quantity ``heat of transport,'' or Q^*, can be expressed as the sum of two distinct contributions. One of these is the partial molal heat of solution of the solute, referred to pure solute as the standard state. The second is a portion, designated the thermal gradient effect, which exists independent of solubility relationships. The latter has been shown to be obtainable from a plot of log solute activity vs reciprocal temperature when the activity is referred to pure solute as the standard state. Comparison of heat of transport with heat of solution in interstitial solid solutions where data are available indicate that the thermal gradient effect is small in these systems.